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Notes: Abstract To investigate the release of endogenous dopamine, noradrenaline and adrenaline in the locus coeruleus, this brain area was superfused with artificial cerebrospinal fluid (CSF) through push-pull cannulae and the release of catecholamines was determined in the superfusate radioenzymatically. Collection of superfusates in time periods of 10 min revealed that release rates of the three catecholamines fluctuated, thus pointing to the existence of ultradian rhythms with following mean periods (minutes per cycle): noradrenaline 52±4, dopamine 37±2, adrenaline 36±2. The rhythm frequency of noradrenaline was significantly lower than the frequencies of dopamine and adrenaline. When the locus coeruleus was superfused with neuroactive drugs, superfusates were collected in time periods of 3 min. Superfusion with tetrodotoxin (1 μmol 1−1) for 12 min elicited a prompt and sustained decrease (−70%) in the release rates of dopamine and adrenaline. The release rate of noradrenaline was also reduced, although to a lesser extent (−40%). Superfusion with veratridine (50 μmol 1−1) led to an immediate and very pronounced enhancement in the release rates of dopamine, noradrenaline and adrenaline. The veratridine-induced increase in catecholamine outflow was decreased strongly by simultaneous superfusion with tetrodotoxin. The findings suggest that the release of endogenous catecholamines in the locus coeruleus fluctuates according to ultradian rhythms. Changes in the release on superfusion with veratridine and tetrodotoxin demonstrate the neuronal origin of the three catecholamines. The observed differences in the release characteristics between noradrenaline on the one hand and dopamine and adrenaline on the other might indicate that noradrenaline is partly released from somatodendritic sites of the noradrenergic cell bodies in the locus coeruleus.

Notes: Abstract Second-order vestibular neurons form the central links of the vestibulo-oculomotor three-neuron arcs that mediate compensatory eye movements. Most of the axons that provide for vertical vestibulo-ocular reflexes ascend in the medial longitudinal fasciculus (MLF) toward target neurons in the oculomotor and trochlear nuclei. We have now determined the morphology of individual excitatory second-order neurons of the anterior semicircular canal system that course outside the MLF to the oculomotor nucleus. The data were obtained by the intracellular horseradish peroxidase method. Cell somata of the extra-MLF anterior canal neurons were located in the superior vestibular nucleus. The main axon ascended through the deep reticular formation beneath the brachium conjunctivum to the rostral extent of the nucleus reticularis tegmenti pontis, where it crossed the midline. The main axon continued its trajectory to the caudal edge of the red nucleus from where it coursed back toward the oculomotor nucleus. Within the oculomotor nucleus, collaterals reached superior rectus and inferior oblique motoneurons. Some axon branches recrossed the midline within the oculomotor nucleus and reached the superior rectus motoneuron subdivision on that side. Since these neurons did not give off a collateral toward the spinal cord, they were classified as being of the vestibulo-oculomotor type and are thought to be involved exclusively in eye movement control. The signal content and spatial tuning characteristics of this anterior canal vestibulo-oculomotor neuron class remain to be determined.

Notes: Abstract Modality specificity of neuronal responses to visual, somesthetic and auditory stimuli was investigated in the anterior ectosylvian cortex (AEC) of cats, using single-unit recording techniques. Seven classes of neurons were found, and according to their responsiveness to sensory stimuli regrouped into three categories: unimodal, bimodal and trimodal. Unimodal cells that responded to only one of the three stimulus modalities formed 59% of the units; 30.2% were bimodal, in that they showed a clear increase of neuronal discharges to two of the three stimulus types; 10.8% were defined as trimodal because they responded to all three stimulus modalities. Although the different categories of cells were intermingled within the AEC, indicating a certain degree of overlap between sensory modalities, some clustering of cell types was nonetheless evident. Thus, the somatosensory responsive cells were mainly located in the anterior two-thirds of the dorsal bank of the anterior ectosylvian sulcus. Visually responsive cells were concentrated on the ventral bank of the sulcus, whereas neurons with an auditory response occupied the banks and fundus of the posterior three-quarters of the sulcus. The histological distribution and physiological properties of AEC neurons suggest that this cortical region is a higher-order associative area whose function may be to integrate information from different sensory modalities.

Notes: Abstract We studied the circuitry between the utricular (UT) nerve and ventral neck motoneurons innervating the longus capitis (LC), a neck flexor muscle, in decerebrate cats. We recorded intracellularly from 63 LC (ipsilateral 37, contralateral 26) motoneurons in C1 and C2 segments. UT nerve stimulation evoked disynaptic, excitatory postsynaptic potentials in all ipsilateral LC motoneurons, and inhibitory postsynaptic potentials that were at least trisynaptic in almost all contralateral LC motoneurons. UT effects on neck motoneurons innervating muscles involved in flexion and lateral turning are similar to the connections between the UT nerve and neck extensor motoneurons. These neuron circuits may play a role in fixing the head and the neck to the body during horizontal linear acceleration.

Notes: Abstract Responsiveness to slits and pattern stimuli was quantified in a total of 68 cells sampled in the posterior extreme of the lateral suprasylvian (PS) cortex as response indices. The cells were studied in relationship to their locations in several subareas of the PS cortex, including areas 19 (n=15) and 21a (n=32) and the posteromedial lateral suprasylvian cortex (PMLS; n=21). These subareas were identified based on retrograde labelling from area 17 and also supplemented with photic responsiveness. This analysis revealed that each cortical area contains cells expressing different combinations of stimulus features. Area 19 contained two major groups of cells: (1) those with strong end-stop selectivity combined with moderate orientation or direction selectivity, and (2) those with weak end-stop selectivity combined with strong orientation selectivity. The groups of cells with strong or moderate orientation selectivity showed a strong preference for stripe over visual noise patterns and relatively large modulatory responses to motion of individual stripes. The PMLS contained one major group of cells with strong end-stop and direction selectivities and with poor orientation selectivity. They also showed stronger preference for visual noise than cells in the other cortical areas and rather weak modulatory responses. Area 21a contained only one group of cells with strong orientation selectivity and length summation property rather than end-stop selectivity, and they also lacked direction selectivity. These cells exhibited a strong preference for stripe patterns and moderate or weak modulatory responses. Altogether, these findings indicate that each cortical area is specialized in expressing different stimulus features. The two groups of cells in area 19 may encode the position and motion of discontinuous visual elements such as corners and line ends and continuous elements such as lines and edges. PMLS cells may encode the motion of single elements or associated motion of multiple discontinuous elements such as textures and backgrounds. Area 21a cells may specifically encode the orientation of long, continuous elements such as lines and edges. In support of this view, two types of statistical analyses demonstrated that the combinations of the response properties expressed in individual PS cells are highly correlated with their locations in cortical areas and that the anatomical locations of individual PS cells are reliably predicted from the sets of response indices expressed in these cells.

Notes: Abstract The present study was performed to clarify whether or not structural plasticity of synaptic connections underlies classical conditioning mediated by the red nucleus (RN) in the cat. Conditioned forelimb flexion is established by pairing electrical conditioned stimuli (CS), applied to corticorubral fibers at the cerebral peduncle (CP), with a forelimb skin shock (the unconditioned stimulus, US), but not by applying the CS alone or by pairing the CS and US at random intervals. In our previous study, it was shown that the firing probability of rubrospinal neurons (RN neurons) in response to the CS was well correlated with acquisition of the conditioned forelimb flexion and that the primary site of neural change underlying establishment of the conditioned forelimb flexion was suggested to be at corticorubral synapses. In the present study, we investigated corticorubral excitatory postsynaptic potentials evoked by CP stimulation (CP-EPSPs), in order to identify the neuronal mechanism underlying establishment of classical conditioning. In normal cats, CP-EPSPs had a typical slow-rising phase, which has been attributed to the distal location of corticorubral synapses on the dendrites of RN neurons. In contrast, in animals that received paired conditioning, subsequent CP stimulation evoked potentials with a fast-rising time course. In control groups of cats that received CS alone, CS randomly paired with the US, or only the same surgical operations as the conditioned animals, most of the CP-EPSPs displayed slow-rising EPSPs that similar to those observed in normal cats. The mean time from onset to peak of the potentials in the conditioned animals was significantly shorter than that seen in other groups. Therefore, the appearance of a fast-rising potential correlates well with acquisition of the conditioned forelimb flexion. The amplitude of the fast-rising potential was gradually changed with stimulus intensity. It had a short onset latency following CP stimulation (0.9 ms), which was similar to that of the slow-rising EPSP in normal cats. It followed high-frequency stimulation up to 100 Hz. These results suggest that the newly appearing, fast-rising potential was a monosynaptically evoked EPSP. Fast-rising EPSPs were also induced by stimulation of the sensorimotor cortex (SM). Since the SM-EPSP was occluded by the CP-EPSP, the SM cortex is, at least in part, a likely source of fast-rising EPSPs. Fast-rising SM-EPSPs were also observed at the unitary level. The SM-EPSPs in the conditioned animals exhibited somatotopical representation in their cortical origin, as has been described in normal cats. The electrotonic length was calculated from the voltage transient responses to current steps injected into the RN neurons. There was no concomitant change in the electrotonic length following the classical conditioning. Furthermore, the fastrising EPSPs were often observed as if they were superposed on the slow-rising EPSPs that were observed in normal animals. These observations suggest that the appearance of fast-rising EPSPs is due to the formation of new corticorubral synapses on the somata or the proximal dendrites of the RN neurons, and not as a result of a reduction in the electrotonic length of the RN neurons. The present study provides further evidence that this type of structural plasticity of synaptic connections underlies establishment of the classically conditioned forelimb flexion.

Notes: Abstract The influence of the corticothalamic projections from somatosensory areas I and II (SI and SII) on the transmission of tactile information through the ventroposterolateral (VPL) thalamus was investigated by examining the effects of cooling-induced, reversible inactivation of SI and/or SII on the responsiveness of 32 VPL neurons to controlled tactile stimulation of the distal forelimb in anaesthetized cats. Both the response levels and spontaneous activity were unaffected in 21 (66%) of the VPL neurons as a result of inactivation of SI or SII singly, or both SI and SII simultaneously. In the remaining 11 neurons, 10 displayed a reduction in response level, an effect observed over the whole of the stimulus-response relations for the neurons studied at different stimulus amplitudes, and one neuron displayed an increase in response level in association with cortical inactivation. When responses in VPL neurons were affected by inactivation of one cortical somatosensory area, they were not necessarily affected by inactivation of the other. Of 14 neurons studied for the effects of the separate inactivation of SI alone and of SII alone, 7 were affected, one from both areas, but the remaining 6 were affected by inactivation of only one of these areas. Phaselocking, and therefore the precision of impulse patterning in the responses of VPL neurons to skin vibration, was unchanged by the cortical inactivation irrespective of whether the response level was affected. The results suggest that SI and SII may exert a facilitatory influence on at least a third of VPL neurons and in this way may modulate the gain of transmission of tactile signalling through the thalamus.

Notes: Abstract The actions of a series of derivatives of 3-aminopropyl-phosphinic acid as baclofen agonists and antagonists have been examined on the synaptic excitation of neurones by impulses in primary afferent fibres in the lumbar spinal cords of pentobarbitone-anaesthetised cats and rats. Both the pre-and postsynaptic inhibitory actions of microelectrophoretic (-)-baclofen were reduced by similarly administered CGP 35 348, 36 742, 46 381, 52 432, 54 626 and 55 845, the latter being the most potent antagonist. None of these antagonists either decreased or increased the excitability of spinal neurones, and the inhibitory action of GABA was reduced only by local concentrations of antagonists which also reduced the action of piperidine-4-sulphonic acid, a GABAA agonist. Although the weak inhibitory effect of 3-aminopropylphosphinic acid in both the rat and the cat was not reduced by these baclofen antagonists, the pre-and postsynaptic inhibitory effects of 3-aminopropyl-methyl-osphinic acid (CGP 35 024), which was more potent than (-)-baclofen, were reduced by the antagonists. Like (-)-baclofen, CGP 35 024 was relatively ineffective in reducing transmitter release in the cord from the terminals of excitatory spinal interneurones, the terminals of excitatory tracts in the dorsolateral funiculus and the cholinergic terminals of motor axon collaterals. In both rat and cat cords, receptors for (-)-baclofen could not be demonstrated to be activated by microelectrophoretic GABA, possibly because of the predominantly dendritic location of GABAB receptors. Spinal pre-and postsynaptic baclofen receptors appeared to be pharmacologically similar but differed from those in the higher central nervous system of the rat, where 3-aminopropylphosphinic acid has been reported to be an effective baclofen agonist. The compounds tested, particularly CGP 55 845 and 46 381, will be of use in further investigations of the physiological relevance of baclofen receptors at central synapses where GABA may be the transmitter.

Notes: Abstract The superior colliculus has long been recognized as an important structure in the generation of saccadic displacements of the visual axis. Neurons with presaccadic activity encoding saccade vectors are topographically organized and form a “motor map.” Recently, neurons with fixation-related activity have been recorded at the collicular rostral pole, at the area centralis representation or fixation area. Another collicular function which deals with the maintenance of fixation behavior by means of active inhibition of orientation commands was then suggested. We tested that hypothesis as it relates to the suppression of gaze saccades (gaze = eye in space = eye in head + head in space) in the head-free cat by increasing the activity of the fixation cells at the rostral pole with electrical microstimulation. Long stimulation trains applied before gaze saccades delayed their initiation. Short stimuli, delivered during the gaze saccades, transiently interrupted both eye and head components. These results provide further support for a role in fixation behavior for collicular fixation neurons. Brainstem omnipause neurons also exhibit fixation-related activity and have been shown to receive a direct excitatory input from the superior colliculus. To determine whether the collicular projection to omnipause neurons arises from the fixation area, the deep layers of the superior colliculus were electrically stimulated either at the rostral pole including the fixation area or in more caudal regions where stimulation evokes orienting responses. Forty-nine neurons were examined in three cats. 61% of the neurons were found to be orthodromically excited by single-pulse stimulation of the rostral pole, whereas only 29% responded to caudal stimulation. In addition, stimuli delivered to the rostral pole activated, on average, omnipause neurons at shorter latencies and with lower currents than those applied in caudal regions. These results suggest that excitatory inputs to omnipause neurons from the superior colliculus are principally provided by the fixation area, via which the superior colliculus could play a role in suppression of gaze shifts.

Notes: Abstract In our previous paper we demonstrated that electrical microstimulation of the fixation area at the rostral pole of the cat superior colliculus (SC) elicits no gaze movement but, rather, transiently suppresses eye-head gaze saccades. In this paper, we investigated the more caudal region of the SC and its interaction with the fixation area. In the alert head-free cat, supra-threshold stimulation in the anterior portion of the SC but outside the fixation area evoked small saccadic shifts of gaze consisting mainly of an eye movement, the head's contribution being small. Stimulating more posteriorly elicited large gaze saccades consisting of an ocular saccade combined with a rapid head movement. At these latter stimulation sites, craniocentric (goal-directed) eye movements were evoked when the cat's head was restrained. The amplitude of eye-head gaze saccades elicited at a particular stimulation site increased with stimulus duration, current strength, and pulse rate, until a constant or “unit” value was reached. The peak velocity of gaze shifts depended on both pulse rate and current strength. The movement direction was not affected by stimulus parameters. The unit gaze vector evoked, in the head-free condition, by stimulating one collicular site was similar to that coded by efferent neurons recorded at that site, thereby indicating a retinotopically coded gaze error representation on the collicular motor map which is not revealed by stimulating the head-fixed animal. Evoked gaze saccades were found to be influenced by fixation behavior. The amplitude of evoked gaze shifts was reduced if stimulation occurred when the hungry animal fixated a food target. Electrical activation of the collicular fixation area was found to mimic well the effects of natural fixation on evoked gaze shifts. Taken together, our results support the view that the overall distribution and level of collicular activity contributes to the encoding of the metrics of gaze saccades. We suggest that the combined levels of activity at the site being stimulated and at the fixation area influence the amplitude of evoked gaze saccades through competition. When stimulation is at low intensities, fixation-related activity reduces the amplitude of evoked gaze saccades. At high activation levels, the site being stimulated dominates and the gaze vector is specified only by that site's collicular output neurons, from which arises the close correspondence between the unit-evoked gaze saccades and the neurally coded gaze vector at that site.

Notes: Abstract The periaqueductal gray (PAG) plays an important role in analgesia as well as in motor activities, such as vocalization, cardiovascular changes, and movements of the neck, back, and hind limbs. Although the anatomical pathways for vocalization and cardiovascular control are rather well understood, this is not the case for the pathways controlling the neck, back, and hind limb movements. This led us to study the direct projections from the PAG to the spinal cord in the cat. In a retrograde tracing study horseradish peroxidase (HRP) was injected into different spinal levels, which resulted in large HRP-labeled neurons in the lateral and ventrolateral PAG and the adjacent mesencephalic tegmentum. Even after an injection in the S2 spinal segment a few of these large neurons were found in the PAG. Wheat germ agglutinin-conjugated HRP injections in the ventrolateral and lateral PAG resulted in anterogradely labeled fibers descending through the ventromedial, ventral, and lateral funiculi. These fibers terminated in lamina VIII and the medial part of lamina VII of the caudal cervical, thoracic, lumbar, and sacral spinal cord. Interneurons in these laminae have been demonstrated to project to axial and proximal muscle motoneurons. The strongest PAG-spinal projections were to the upper cervical cord, where the fibers terminated in the lateral parts of the intermediate zone (laminae V, VII, and the dorsal part of lamina VIII). These laminae contain the premotor interneurons of the neck muscles. This distribution pattern suggests that the PAG-spinal pathway is involved in the control of neck and back movements. Comparing the location of the PAG-spinal neurons with the results of stimulation experiments leads to the supposition that the PAG-spinal neurons play a role in the control of the axial musculature during threat display.

Notes: Abstract Binocular non-dominant suppression (NDS) in the dorsal lateral geniculate nucleus (LGNd) of the cat was studied by recording from single neurons in the LGNd of anaesthetized, paralysed cats while stimulating the non-dominant eye with a moving light bar. The maintained discharge rate of LGNd neurons was varied by stimulating the dominant eye in various ways: by varying the size or contrast of a flashed spot, by varying the inner diameter of a flashed annulus of large outer diameter, by varying the velocity of a moving light bar, and by covering the eye. Non-dominant suppression was quantified either as the decrease in the maintained discharge rate (the “dip”), expressed as spikes per second, or as the ratio of the dip to the maintained discharge rate (the “dip ratio”). At low maintained discharge rates the dip, although low in value, frequently approached the maintained rate, i.e. the dip ratio approached unity. As the maintained discharge rate increased the dip value also increased, but more slowly than the maintained discharge rate, i.e. the dip ratio decreased. At maintained discharge rates above about 30 spikes/s, in many neurons the dip appeared to be approaching a constant value. This strong dependence of NDS on the maintained discharge rate of the LGNd neuron suggests that the inhibitory input to the cell arises from a region of the brain that receives an input both from the non-dominant eye and from the LGNd cell. Reasons are given for thinking that this region is the perigeniculate nucleus. Because of the strong dependence of dip and dip ratio on the maintained discharge rate, it was necessary to adopt stringent criteria when comparing NDS in two different sets of neurons or of the same set of neurons in different conditions. We recognized a significant difference in NDS between two classes of neurons or between two states only if: (1) there was no significant difference between the maintained discharge rates, and (2) there was a significant difference for both dip and dip ratio between the two classes or states. Using these criteria we found: (1) no difference between non-lagged X (XNL) and non-lagged Y (YNL) cells, (2) no difference between on-centre and off-centre cells for either XNL or YNL cells, (3) no difference between XNL cells and lagged X (XL) cells. However, there was a significant difference between cells in lamina A and those in lamina A1 for both XNL and YNL cells, dip and dip ratio values being about twice as great in lamina A. In cats in which one optic nerve had been pressure-blocked so as to prevent conduction in the largest axons (Y fibres), loss of conduction in Y fibres crossing the chiasm and projecting to the contralateral LGNd did not affect NDS. Loss of conduction in Y fibres projecting to the ipsilateral LGNd caused a complete loss of NDS in the non-lagged Y cells of lamina A and a substantial decrease in the NDS of the nonlagged X cells of lamina A. The latter cells must, therefore, be partly suppressed by non-Y fibres, presumably X fibres. It also follows that all the NDS of cells in lamina A1 is mediated by non-Y fibres, probably X fibres. Thus, NDS in the cat is partly class-specific and partly not. The discharge of retinal ganglion cells also protects the LGNd cells against NDS. The contribution of Y fibres to this anti-suppressive action was also examined. Contralaterally projecting Y fibres make no contribution. Ipsilaterally projecting Y fibres exert an anti-suppressive action on non-lagged X cells in lamina A1. It follows also that the anti-suppressive action on cells in lamina A mediated by contralaterally projecting fibres is due to non-Y fibres, presumably X fibres. Thus, both the suppressive and the anti-suppressive actions of Y fibres are mediated only by the uncrossed pathway.

Notes: Abstract The relationship between changes in posture and the performance of a forelimb movement required for a transition between two stance positions was analysed in cats. The task consisted of an operantly conditioned, forelimb stepping movement from one support platform to another located more anterior. The reward was given only after a specific vertical force was applied to the second platform. This ensured that the cat performed a clear transition from its initial stance posture to another requiring a different weight distribution. The strategy adopted by an animal during the conditioned movement was studied by analysing the distribution of the vertical forces as a function of time. Specific quantitative functions were used to describe the weight distribution in the anterior-posterior, right-left and diagonal directions as the task was performed. The temporal parameters characterising this behaviour were not significantly different between animals, except for reaction times. In contrast, spatial parameters reflected in the distribution of vertical forces generated during the performance of the task were characteristic for each animal. As a consequence, a variety of strategies were employed. Nevertheless some general features were found, including the persistence of a diagonal support pattern during the phasic part of the movement, and an initial movement to the side of the forepaw performing the movement. The findings support the view that each animal exhibits a specific strategy for performing this well-learned task, and that the strategy is consistently employed over consecutive trials of the movement.

Notes: Abstract The present study was aimed at elucidating the pontomedullary and spinal cord mechanisms of postural atonia induced by microinjection of carbachol and restored by microinjections of serotonin or atropine sulfate into the nucleus reticularis pontis oralis (NRPo). Medullary reticulospinal neurons (n=132) antidromically activated by stimulating the L1 spinal cord segment were recorded extracellularly. Seventy-eight of them were orthodromically activated with mono- or disynaptic latencies by stimulating the NRPo area at the site where carbachol injections effectively induced postural atonia. Most of these reticulospinal neurons (71 of 78) were located in the nucleus reticularis gigantocellularis (NRGc). Following carbachol injection into the NRPo, discharge rates of the NRGc reticulospinal neurons (29 of 34) increased, while the activity of soleus muscles decreased bilaterally. Serotonin or atropine injections into the same NRPo area resulted in a decrease in the discharge rates of the reticulospinal neurons with a concomitant increase in the levels of hindlimb muscle tone. Membrane potentials of hindlimb extensor and flexor alpha motoneurons (MNs) were hyperpolarized and depolarized by carbachol and serotonin or atropine injections, respectively. In all pairs of reticulospinal neurons and MNs (n=11), there was a high correlation between the increase in the discharge rates and the degree of membrane hyperpolarization of the MNs. Spike-triggered averaging during carbachol-induced atonia revealed that inhibitory postsynaptic potentials (IPSPs) were evoked in 15 MNs by the discharges of nine reticulospinal neurons. Four of them evoked IPSPs in more than one MN. The mean segmental delay and the mean time to the peak of IPSPs were 1.6 ms and 2.0 ms, respectively. Axonal trajectories of reticulospinal neurons (n=6), which evoked IPSPs in MNs, were investigated in the lumbosacral segments (L1-S1) by antidromic threshold mapping. The stem axons descended through the ventral (n=2) and ventrolateral (n=4) funiculi in the lumbar segments. All axons projected their collaterals to the intermediate region (laminae V, VI) and ventromedial part (laminae VII, VIII) of the gray matter. All these results suggest that the reticulospinal pathway originating from the NRGc is involved in postural atonia induced by pontine microinjection of carbachol, and that the pathway is inactivated during the postural restoration induced by subsequent injections of serotonin or atropine. It is further suggested that the pontine inhibitory effect is mediated via segmental inhibitory interneurons projecting to MNs.

Notes: Abstract Receptive field properties of extracellularly recorded units in the visual cortex (area 17) of cats made bilaterally amblyopic by a variety of rearing conditions were measured and compared with the properties of units in normal cats. Properties studied included sensitivity to vernier offset, response facilitation to increasing bar length, receptive field size, responsiveness to moving and flashed stimuli, orientation tuning, the relation between mean firing rate and its variance, the amount of overlap of regions of on and off responsiveness in simple and complex cells, and, for flashed stimuli, latency to response onset, time to peak response, and response decay time constant. Behavioural testing of the amblyopic animals showed that spatial resolution was 2–4 times lower and vernier acuity thresholds 10–20 times greater than normal. Despite this, several neuronal response properties did not differ significantly from those in normal animals. These included peak responsiveness to moving stimuli, widths of orientation tuning curves, response variability, and latency to initial response for flashed stimuli. Other properties showed small but significant changes. Sensitivity to vernier offset (impulses per degree of offset) was reduced to nearly half its normal level; receptive field sizes increased by about 24% and an incomplete segregation of regions of on and off responsiveness was found in some cells, which made them hard to classify as simple or complex. Responses to flashed stimuli were smaller and more persistent. Their statistical significance notwithstanding, it seems unlikely that these relatively small response abnormalities in area 17 can fully account for the observed behavioural deficits.

Notes: Abstract It has been previously shown that phasic stimulation of group I afferents from ankle and knee extensor muscles may entrain and/or reset the intrinsic locomotor rhythm; these afferents are thus acting on motoneurones through the spinal rhythm generators. It was also concluded that the major part of these effects originates from Golgi tendon organ Ib afferents. Transmission in this pathway to lumbar motoneurones has now been investigated during fictive locomotion in spinal cats injected with nialamide and l-DOPA, and in decerebrate cats with stimulation of the mesencephalic locomotor region. In spinal cats injected with nialamide and l-DOPA, it was possible to evoke long-latency, long-lasting reflexes upon stimulation of high threshold afferents before spontaneous fictive locomotion commenced. During that period, stimulation of ankle and knee extensor group I afferents evoked oligosynaptic excitation of extensor motoneurones, rather than the “classical” Ib inhibition. Furthermore, a premotoneuronal convergence (spatial facilitation) between this group I excitation and the crossed extensor reflex was established. During fictive locomotion, in both preparations, the transmission in these group I pathways was phasically modulated within the step cycle. During the flexor phase, the group I input cut the depolarised (active) phase in flexor motoneurones and evoked EPSPs in extensor motoneurones; during the extensor phase, the group I input evoked smaller EPSPs in extensor motoneurones and had virtually no effect on flexor motoneurones. The above results suggest that the group I input from extensor muscles is transmitted through the spinal rhythm generator and more particularly, through the extensor “half-centre”. The locomotor-related group I excitation had a central latency of 3.5–4.0 ms. The excitation from ankle extensors to ankle extensors remained after a spinal transection at the caudal part of L6 segment; the interneurones must therefore be located in the L7 and S1 spinal segments. Candidate interneurones for mediating these actions were recorded extracellularly in lamina VII of the 7th lumbar segment. Responses to different peripheral nerve stimulation (high threshold afferents and group I afferents bilaterally) were in concordance with the convergence studies in motoneurones. The interneurones were rhythmically active in the appropriate phases of the fictive locomotor cycle, as predicted by their response patterns. The synaptic input to, and the projection of these candidate interneurones must be fully identified before their possible role as components of the spinal locomotor network can be evaluated.

Notes: Abstract Retinal ganglion cells of adult cats have the potential to regenerate their axons into autografted peripheral nerve. Two months after transplantation of the sciatic nerve to the axotomized optic stump, regenerated axons were labeled anterogradely with biocytin, and myelin formation by Schwann cells was examined electron microscopically. Both myelinated and unmyelinated fibers were labeled with biocytin. Among 511 axons labeled in three grafts, 96 fibers (18.8%) were myelinated and 415 (81.2%) were unmyelinated. Mean diameter with SD of myelinated fibers was 1.28 ± 0.39 μm (range 0.71–2.47) and that of unmyelinated fibers was 0.76± 0.38 μm (range 0.18–2.46). The ratio of inner to outer diameters of the myelin sheath (g value) was 0.82, which is close to the value (0.8) for the optic fibers of intact adult cats.

Notes: Abstract Motor learning can be demonstrated in the vestibulo-ocular reflex (VOR) by changing its gain (eye velocity/head velocity) with goggles and optokinetic (OK) drums. It is known that the flocculus is essential for this plasticity but there is controversy about whether the modifiable synapses mainly responsible are in the flocculus. To investigate this further we utilized the known reciprocal relationship between complex spikes and simple spikes in Purkinje cell discharges. By stimulating climbing fibers from the olive to the flocculus at 7 Hz, the simple spike rate of almost all recorded floccular cells could be driven to zero. This was termed floccular shutdown and is felt to effect a functional, reversible flocculectomy. Sixty single units in the flocculi of four cats were recorded. Stimulation of the climbing fibers at 7 Hz caused the discharge rate to decrease to zero in 95% of these cells. The gain of the horizontal VOR in three cats was driven repeatedly to twice or half its normal value by rotation within a moving OK drum and also by wearing magnifying or fixed-field goggles; this process required 3 days. If, on the 4th day, the cat was exposed to an OK drum rotating in the opposite direction, the gain was driven back to normal in 30 min. If, however, the climbing fibers were stimulated at 7 Hz during these 30 min, the gain did not return — learning was blocked. This verified that loss of floccular activity by this method abolishes VOR gain plasticity. Moreover, when 7 Hz stimulation first began, after 3 days of adaptation, the adapted gain remained at its adapted value, either half or twice normal, even in the face of floccular shutdown. This result appears incompatible with the hypothesis that the modifiable synapses are in the flocculus.

Notes: Abstract Excitatory receptive field (ERF) response profiles and length summation functions were derived from complex neurones in cat striate cortex. Measured length summation was compared with summation predicted from integration over ERF profiles. In a minority of neurones, measured and predicted summation were well matched. In the majority, whether end-stopped or not, responsiveness in length summation tests was appreciably greater than predicted for short stimuli, compared with ERF profiles. The mismatch was least in standard and greatest in special complex neurones; in the latter group, response levels to long stimuli fell well below predicted levels. In end-stopped neurones the decremental portion of length summation functions was not predicted by ERF profiles. These results implicate the involvement of non-linear mechanisms, whereby concomitant stimulation of central regions of the receptive field (RF) potentiate the efficacy of loci towards either end of the RF.

Notes: Abstract Width summation of complex neurones in cat striate cortex was assessed for moving sine-wave gratings. Summation was restricted in special complex neurones, approximately matched receptive field width in intermediate complex neurones and exceeded it in most standard complex neurones. Responses to preferred and opposite directions of motion were compared: 12 of 20 complex neurones showed similar directional bias for moving sinewave gratings and for single moving bars of either contrast polarity; 8 of 20 were similarly or more weakly direction-selective for bars than for grating patches, dependent on patch width. In two of these, this was despite the fact that the directional bias for gratings was invariant with patch width. In the remaining six, differences could be accounted for by progressive increase or decrease in directional bias for gratings, as grating patch width was systematically increased. In conclusion, directional bias of a substantial proportion of complex cells is determined by stimulus configuration.

Notes: Abstract The dependency of intrageniculate signal transfer on stimulus temporal frequency was investigated by comparing responses of individual X-relay cells with their direct retinal inputs in anesthetized and paralyzed cats. Temporal frequency response functions of lateral geniculate nucleus (LGN) X-cells were more narrowly tuned than those of their retinal inputs. The efficiency of signal transfer was consistently highest at or around the geniculate cells' optimal temporal frequency, and the degree of signal transfer, which was more closely related to the LGN cells' firing rate than to the firing rate of their retinal input, decreased for both lower and higher temporal frequencies. The high temporal frequency cut-offs were significantly lower in geniculate cell responses than those of their direct retinal inputs. This reduction in temporal resolution was exaggerated for relatively low stimulus spatial frequencies. The present results provide clear evidence for the notion that LGN cells function as nonlinear temporal filters and that this stimulus-dependent signal transmission appears to be regulated by complex local mechanisms.

Notes: Abstract Interstitial and tissue cations and electrical potential were studied in an experimental model of spinal cord contusion injury in anaesthetised cats. Measurements of interstitial ion activity in the grey matter at the injury site (with ion-selective electrodes), showed a decrease of sodium and calcium, an increase of potassium, a small acidification and a negative shift in the electrical potential 5 min after injury. The interstitial ionic changes were completely reversible within 90 min following injury. Measurements of the ion content in a tissue sample from the injury site (flame photometry) showed an increase of sodium and calcium and a decrease of potassium 5 min after injury. The magnitude of the post-injury sodium change was much larger than the potassium change, both for interstitial and tissue measurements. Treatment of the animals with the calcium entry blocker flunarizine before the injury did not influence the magnitude of post-injury interstitial calcium decrease but significantly increased the rate of subsequent recovery. Pre-injury flunarizine treatment also significantly increased the recovery rate of the electrical potential. The experiments suggest the occurrence of a net ionic shift towards the intracellular space, which may contribute to oedema formation in the very early post-injury period. The post-injury decrease of interstitial calcium activity is probably not mediated by flunarizine-sensitive calcium entry mechanisms; such mechanisms may, however, be involved in the subsequent recovery period for interstitial calcium activity. Calcium ions may be involved in the recovery process of the negative electrical potential after injury.

Notes: Abstract Responses of simple and complex cells in cat striate cortex were studied with moving sine-wave gratings before and during application of the GABAA receptor antagonist bicuculline methiodide. Both simple and complex cells exhibited a broadening of their spatial frequency tuning functions under bicuculline. This was especially evident at spatial frequencies lower than the ones the cell was responding to before the drug administration. The effects cannot be explained by response saturation and could be reversed by cessation of the iontophoresis. The results indicate that the band-pass response characteristics of the spatial frequency response functions of striate cells derive largely from intracortical inhibition. The findings have implications also for the orientation selectivity of cortical cells. Since many geniculate cells are tuned for stimulus orientation at higher spatial frequencies, suppression of the low-spatial-frequency component would remove some of the orientation non-specific response in striate cortical cells and contribute to their orientation selectivity.

Notes: Abstract The aim of this study was to gain information from anesthetized cats about the differential coding properties of neurons in the three major subdivisions of the inferior colliculus: the central (CNIC) and external (EN) nuclei and dorsal cortex (DC). Stimuli were presented in the free field from a speaker facing the contralateral pinna. For each unit, the characteristic frequency (CF, where threshold was lowest) was determined, and impulse rates to CF tone bursts, noise bursts and four feline vocal stimuli were measured as a function of increasing sound pressure level (rate/level functions). Peristimulus-time histograms were computed for responses to all stimuli. Sustained firing patterns to CF stimuli were observed for 81% of units in CNIC, for 50% of units in EN and 27% of units in DC. Sustained discharges were evoked by noise in 78–100% of units in all regions, and by at least one vocal stimulus in 86% of units in CNIC, 82% in EN and 55% in DC. In the CNIC, non-monotonic rate/level functions to CF stimuli were more common (41%) than either monotonie or plateau functions, whereas the reverse was the case with noise and vocal stimuli. Non-monotonic functions were uncommon to any stimulus in EN and DC (21–24%). Vocal stimuli were more effective in terms of higher firing rates than noise or CF stimuli in 27% of units in CNIC, 82% in EN and 72% in DC. There were no units that responded exclusively to one vocal stimulus, but a high proportion of units in EN responded strongly to broad band stimuli, and some of these showed clear preferences for one vocal stimulus over others.

Notes: Abstract Localization and projection to the phrenic (PH) nucleus were studied in a sample of premotor neurons that directly projected to hypoglossal motoneurons (XII Mns) and showed respiratory-related patterns of activity. The experiments were carried out in cats, under pentobarbital anesthesia. In the first part of the study, the retrograde double-labeling technique was used to reveal the existence of neurons projecting to both the XII and the PH nuclei. Injection of a fluorescent dye (fast blue, FB) into the XII nucleus and another (nuclear yellow, NY) into the PH nucleus retrogradely labeled, with either FB or NY, medullary reticular neurons mainly in the regions ventrolateral to the nucleus of the tractus solitarius (vl-NTS), ventrolateral to the hypoglossal nucleus (vl-XII), and dorsomedial to the nucleus ambiguus (dm-AMB) bilaterally. In addition, some neurons in these regions were labeled with both FB and NY. In the second part of the study, unitary activity was recorded extracellularly from medullary respiratory neurons. In the regions vl-NTS, vl-XII, and dm-AMB, inspiratory neurons were found which antidromically responded to stimulation of the XII nucleus. Some of them also responded antidromically to stimulation of the PH nucleus. Averaging of rectified and integrated XII and PH nerve discharges by spontaneous spikes of single inspiratory neurons in the vl-NTS and dm-AMB regions revealed a facilitation in either XII nerve discharge or both XII and PH nerve discharges after a short latency of monosynaptic range. It is concluded that in the vl-NTS and dm-AMB regions there are inspiratory neurons that are excitatory premotor neurons projecting to XII Mns showing the respiratory-related activity. Some of them have excitatory synaptic connections to XII and PH Mns via bifurcating axons.

Notes: Abstract Directional tuning for motion of a long bar and a spot was compared quantitatively over a wide range of velocities in 23 simple cells of cat striate cortex whose “on” and “off” receptive field subregions had been mapped with optimally oriented, stationary flash-presented bars. Tuning curves were derived using stimuli whose polarity of contrast was appropriate for the dominant receptive field subregion of each cell (i.e. light stimuli for on-subregions and dark stimuli for off-subregions); stimulus sweep was centred accurately on the centre of that subregion. Bar stimuli were of optimal width, and spot diameter was equal to the width of the bars. In all simple cells, preferred axis of motion for a long bar was invariant with velocity, being orthogonal to preferred orientation, as assessed with a stationary flash-presented bar. In 20 of 23 simple cells, preferred axis for spot motion was approximately orthogonal to that for bar motion (i.e., parallel to preferred orientation) at all velocities tested, including those just above threshold for spot stimuli. However, tuning for the spot became sharper as velocity was increased, due to an increase in response to the spot moving along the preferred axis and a decrease in response to spot motion along other axes, including the preferred axis for the bar. Both preferred and upper cut-off velocity were consistently higher for spot than for bar motion. The remaining 3 simple cells showed no response to spot motion at any velocity, and their preferred axis of motion for the shortest bar which evoked a consistent response was the same as that for a long bar. We conclude that simple cells respond to motion of a spot per se and not just to its oriented components, and that in most simple cells preferred axis for spot motion is genuinely approximately orthogonal to that for motion of a long bar. A spatio-temporal filter model incorporating intracortical feedforward facilitation along the long axis of the receptive field can account for the observed differences in axis preference and velocity sensitivity for spot and bar motion.

Notes: Abstract Mach bands are a visual illusion evoked by a luminance ramp dividing two luminance plateaux (blurred edges), but not by sharp edges. Recently, two physiology-based models have tried to cope with the psychophysical data concerning this phenomenon. The basic components of both models are neurons with even- or odd-symmetric receptive fields (RFs). Both models predict that odd-symmetric cells respond better to sharp edges, while even-symmetric cells respond better to blurred ones. We have measured the responses of 34 primary visual cortex simple cells of the cat to blurred edges of various degrees. Twenty-one cells had RFs of even symmetry, responding best to blurred edges than to sharp ones. The rest were odd-symmetric cells, of which 12 responded best to sharp edges, and only one exceptional cell responded best to a 0.85°-wide edge. Thus, the different cell types responded as predicted by the two different Mach band models. Simple cells may thus serve as the physiological basis of the psychophysical phenomenon of Mach bands. Furthermore, our evidence suggests the existence of inhibition between odd-and even-symmetric cells, as predicted by one of the models.

Notes: Abstract In order to gain insight into the representation of articular pain of the knee at the supraspinal level, recordings were made from lateral thalamic neurons receiving input from afferent fibres of the knee joint in chloralose-anaesthetized cats. Dorsoventral penetrations were made through the ventral posterior lateral nucleus (VPL) using high intensity electrical stimulation of the medial articular nerve (MAN), which contains a high proportion (80%) of Aδ and C afferent fibres. All recording sites were verified histologically. Close retrograde injections (300 μl over 6 s) into geniculate artery of KCl (2 × isotonic), bradykinin (BK, 2.6 or 26 μg) and capsaicin (200 μM) were used to test the response properties of thalamic neurons. Of the 50 MAN-positive units tested, 20 showed a response to intra-arterial KCl; of these 20, 12 had a response to BK; 8 of these 12 units were additionally tested with capsaicin and all responded. KCl and capsaicin injections had similar mean response latencies (4.5 and 6.8 s), whereas BK had a longer mean latency (18.6 s). The mean peak response was greatest for capsaicin (168 impulses/s), then KCl (87.5 imp/s) and least with BK (36.4 imp/s). The mean response duration was longest with capsaicin (118 s), followed by BK (67.5 s) and least with KCl (27.9 s). Most of these were convergent wide dynamic range (WDR) neurons with a deep receptive field in the knee joint and hindlimb muscle and/or cutaneous distal hind limb digit, located to the dorsal or ventral periphery of the lateral division of the VPL, the VPLl. In addition, 8 neurons showed inhibitory responses to KCl and/or BK injections. The background activity of the VPLl neurons activated by saphenous nerve stimulation was inhibited by the nociceptive articular stimulus with a magnitude and time course which mirrored the excitatory responses in the periphery of VPLl. These results support the concept that the lateral thalamus plays an important role in mediating discriminative aspects of joint pain.

Notes: Abstract This is a study of the tendon jerk reflex elicited by a brief stretch applied to the triceps surae muscle group in the chloralose-anaesthetised cat. The size of the recorded reflex depended on stretch parameters (optimum at 300 μm amplitude at a rate of 100 mm/s) and on how the muscle had been conditioned. A reflex elicited after a conditioning contraction at the test length was often twice as large as after a contraction carried out at a length longer than the test length. This difference was attributed to the amount of slack introduced in the intrafusal fibres of muscle spindles by conditioning. The question was posed, did ongoing fusimotor activity exert any influence on the size of the tendon jerk? Depolarization indices (DPI) were calculated from responses of muscle spindles to stretch and correlated with the level of reflex tension. Values of DPI obtained from afferent responses with and without repetitive stimulation of identified fusimotor fibres suggested that with the stretch parameters used here the main influence of fusimotor activity was that it removed any pre-existing slack in muscle spindles and thereby increased reflex tension. In the absence of intrafusal slack, stimulation of static and dynamic fusimotor fibres had little additional influence on the size of the reflex. It is concluded that much of the variability typically seen with tendon jerks is due to muscle history effects. Since in muscles which have not been deliberately conditioned there is commonly some slack present in spindles, activity in fusimotor fibres is likely to reduce slack and therefore increase reflex size.

Notes: Abstract Bilateral surgical lesions of the flocculus or the nodulo-uvular lobes were performed in the cat. Effects of these lesions on optokinetic and optokinetic afternystagmus (OKAN), vestibulo-ocular reflex (VOR), visual suppression, and adaptation and habituation of VOR were studied using an identical experimental protocol. After flocculectomy, all these functions were impaired, except for habituation. Long-term postoperative recordings only revealed a recovery of the suppression of VOR, suggesting a limited contribution of the flocculus to this function. After nodulo-uvulectomy, only habituation and OKAN were modified. When the lesion was restricted to part of the uvula, OKAN duration was decreased. For other lesions involving the uvula together with the nodulus and/or the lobules VII-VIII, OKAN duration was increased. Habituation was lost after destruction of the nodulo-uvular lobes. When this latter structure was damaged, the retention component of habituation was selectively impaired, sparing the acquisition. Additional lesions outside the vestibulocerebellum appeared necessary to suppress the two components. Comparison of results obtained after flocculectomy and after nodulouvulectomy confirms and extends to nonprimate species the concept of a “differential control” of adaptation and habituation by distinct vestibulocerebellar structures.

Notes: Abstract The focus of these experiments was to determine the relationships between head movement, neck muscle activation patterns, and the positions and movements of the cervical vertebrae. One standing cat and one prone cat were trained to produce voluntary sinusoidal movements of the head in the sagittal plane. Video-opaque markers were placed on the cervical vertebrae, and intramuscular patch electrodes implanted in four muscles of the head and neck. Cinefluoroscopic images of cervical vertebral motion and electromyographic responses were simultaneously recorded. Analysis of the spinal movement revealed that the two cats used different strategies to keep their heads aligned with the tracker. In the standing cat, vertebral motion described a more circular arc, compared to a forward diagonal in the prone cat. Intervertebral motion was limited, but more acute angles appeared between the vertebrae of the prone lying than of the standing animal. Data revealed that the central nervous system could control several axes of motion to keep the cervical spine matched to the moving stimulus. Phase relations between the sinusoidal motion of the vertebral column, peak activation of the neck muscles, and that of the stimulus were examined, and several different control strategies were observed both between and within animals. The results suggest that the central nervous system engages in multiple strategies of musculo-skeletal coordination to achieve a single movement outcome.

Notes: Abstract The discharge frequency of primary (Ia) and secondary (II) muscle spindle afferents from the tibial anterior muscle of the cat were recorded under a rampand-hold stretch of the host muscle. The rate of ramp stretch and the prestretch of the muscle were varied systematically. The degree of stretch was kept constant. For a discharge pattern recorded at a ramp rate of 10 mm/s, the peak dynamic discharge, the maximum static value and the final static value were determined. These three discharge rate values were plotted against the maximum static value. In the resulting charts the II afferents presented themselves as a homogeneous group of spindle afferents, whereas the Ia fibers separated into three subgroups. The existence of three subpopulations of Ia fibers was verified by the method of Hald. Furthermore, it is shown that each subpopulation generated its discharge patterns in its own regularly systematic manner. It was concluded that, as one of the three Ia subpopulations exhibits much the same dynamic and static stretch properties as the II fibers, the encoder of this subpopulation must receive its receptor current from the sensory terminals of passive intrafusal chain fibers. The encoder of a second Ia subpopulation indicates its action potentials using the receptor current stemming from the bag1 sensory terminals, these Ia fibers eliciting a slow adaptation component of a high magnitude which is assumed to be the consequence of a high level of “creep” in the passive intrafusal bag1 fiber. The third Ia subpopulation initiates its action potential sequences by means of the receptor current stemming from the passive bag2 fiber, producing behavior patterns that lie between those of the other two Ia subpopulations.

Notes: Abstract The possible role of GABAergic mechanisms in the control of the basal ganglia output structures, the globus pallidus (GP) and the entopeduncular nucleus (EP), was studied in cats performing a conditioned flexion movement triggered by an auditory stimulus. The effects of discrete unilateral microinjections of low doses of the GABAA receptor agonist (muscimol 5–100 ng/ 0.5 μl) and antagonist (bicuculline methiodide 25–150 ng/0.5 μl) in the GP and the EP were tested on the motor performance of eight animals trained to release a lever in a simple reaction time (RT) schedule after an auditory stimulus. Control injections in neighboring structures did not induce any effect except with five- to tenfold higher doses in the closest injection sites. The dose of 20 ng muscimol injected into the ventral and medial part of the GP produced an arrest of the performance after a few unsuccessful trials (over the RT reinforcement limit of 500 ms), while muscimol injected in sites located in the lateral GP resulted in a dose-dependent lengthening in RTs, with a concomitant increase in the force change latency. In most of the subjects, the force exerted on the lever was higher after muscimol than after vehicle injection. Force change velocity was then significantly increased. In contrast, muscimol injected in the ventral and rostral region of the EP produced a decrease in RTs or a complete cessation of responding after a high number of anticipatory responses (release of the lever before the trigger stimulus). No significant changes in the force change latency could be observed while there was a non-significant tendency for the force levels to be lowered. Bicuculline injections in the EP were found to increase RTs with a concomitant increase in force change latency and a slowness of velocity, while no significant effect was observed following injections in the GP. These results suggest that a balance between GABAergic activity in the two output nuclei of the basal ganglia, the GP and the EP, is crucial for the correct initiation and execution of the conditioned motor task.

Notes: Abstract The tonotopicity of the cat's primary auditory cortex (AI) is thought to provide the framework for frequency-specific processing in that field. This study was designed to assess this postulate by examining the spatial distribution of neurons within AI that are activated by a single tonal frequency delivered to the contralateral ear. Distributions obtained at each of several stimulus levels were then compared to assess the influence of stimulus amplitude on the spatial representation of a given stimulus frequency in AI. Data were obtained from 308 single units in AI of four adult, barbiturate-anesthetized cats, using extracellular recording methods. Stimuli were 40-ms tone pulses presented through calibrated, sealed stimulating systems. In each animal, the CF (stimulus frequency to which the unit is most sensitive), threshold at CF, response/level function at CF, and binaural interactions were determined for isolated neurons (usually one per track) in 60–90 electrode tracks. For each unit, regardless of its CF, responses to 40 repetitions of contralateral tones of a single frequency, presented at each of four or five sound pressure levels (SPLs) in the range from 10 to 80 dB were obtained. Different test frequencies were used in each of four cats (1.6, 8.0, 11.0, and 16.0 kHz). For tones of each SPL, we generated maps of the response rates across the cortical surface. These maps were then superimposed on the more traditional maps of threshold CF. All units whose CF was equal to the test frequency could be driven at some SPL, given an appropriate monaural or binaural configuration of the stimulus. There was a clear spatial segregation of neurons according to the shapes of their CF tone response/level functions. Patches of cortex, often occupying more than 2 mm2, seemed to contain only monotonic or only nonmonotonic units. In three cortices, a patch of nonmonotonic cells was bounded ventrally by a patch of monotonie cells, and in one of these cases, a second patch of monotonic cells was found dorsal to the nonmonotonic patch. Contralateral tones of any given SPL evoked excitatory responses in discontinuous cortical territories. At low SPLs (10, 20 dB), small foci of activity occurred along the isofrequency line representing the test frequency. Many of these cells had nonmonotonic response/level functions. At mid- and high SPLs, the CFs of neurons activated by a pure tone varied across 3 octaves. At the highest SPL used (80 dB), most of the neurons with nonmonotonic response/level functions were inactive, or responded poorly; the active neurons were widely spread across the cortex, and the distribution of activity had a pattern bearing little relationship to the threshold CF contour map. These data indicate that only isolated patches of units within the relevant isofrequency contour are activated by a given suprathreshold contralateral tone. At suprathreshold stimulus levels, the region of cortex containing active patches extends widely beyond the threshold isofrequency contour region corresponding to the test stimulus frequency. The spatial representation of a stimulus delivered to the contralateral ear appears, therefore, to be highly level dependent and discontinuous. These observations suggest that in the cat's AI, tonotopicity and isofrequency contours are abstractions which bear little resemblance to the spatial representation of tonal signals.

Notes: Abstract This report describes the effects of succinylcholine (SCh) on the secondary endings of cat soleus muscle spindles and attempts to explain them in terms of the action of the drug on intrafusal fibres. All but 2 of 41 secondary endings studied in detail showed a significant response to a single intravenous injection of 200 μg kg-1 SCh. This consisted of a rise in the resting rate or development of a resting discharge if the spindle had previously been silent and an increase in the response to stretch. The increases in the responses to stretch were weaker than those observed for primary endings of spindles, but were much larger than those of tendon organs, which showed very little effect with this concentration of drug. The response to SCh showed two features consistent with its action being mediated via an intrafusal muscle fibre contraction rather than a direct depolarising action on the afferent nerve ending. In the presence of SCh, secondary endings were able to maintain a discharge during muscle shortening at rates, on average, more than 5 times greater than under control conditions. Secondly, the increase in spindle discharge produced by SCh showed a length dependence similar to that for fusimotor stimulation. Further support for the action of SCh being principally via an intrafusal fibre contraction was provided by the observation that its effects were abolished by the neuromuscular blocker gallamine triethiodide. The time course of recovery of SCh responses, following their blockade by gallamine, was much slower than recovery of extrafusal tension and closely paralleled that for the recovery of fusimotor responses. In three separate experiments on the medial gastrocnemius muscle the possibility that SCh may exert an excitatory action on spindle sensory endings through the liberation of potassium ions from the muscle was tested by tetanic stimulation of the muscle. This had no detectable excitatory effect. Several observations were made on the effect of SCh on responses of cutaneous receptors. SCh did not change levels of spontaneous activity or responses to mechanical stimulation of either slowly or rapidly adapting mechanoreceptors. It was argued for both tendon organs and cutaneous receptors that if SCh had a direct action on the nerve ending at the concentrations used here, some responses of these receptors to the drug might have been expected. All of the above supports the view that secondary endings of spindles are able to respond to SCh by the development of an intrafusal fibre contracture. The question of the intrafusal fibre types involved is discussed.

Notes: Abstract Long-term potentiation of synaptic transmission (LTP), as documented by the enhancement of evoked field potentials in layer III following stimulation of the underlying white matter, has been studied in slices of motor cortex from adult cats. With a 1 M NaCl-filled recording electrode, LTP was induced only in one out of eight slices. When the recording electrode in addition contained 5 mM bicuculline metiodide, LTP was obtained with a much higher rate of success (15/19), suggesting that reduction of GABAA receptor-mediated inhibition facilitated the induction of LTP in the motor cortex. Bath application of dl-2-amino-5-phosphonovaleric acid (APV, 100 μM) or Ni2+ (100 μM) significantly reduced the success rate for LTP occurrence (6/16 and 5/16, respectively); but when LTP was induced, it did not show significant change in magnitude and time course. In slices perfused with APV (100 μM) plus Ni2+ (100 μM), LTP induction was completely blocked (0/12). These results suggest that two different mechanisms may subserve LTP induction in the cat motor cortex: one is mediated by N-methyl-d-aspartate receptors and can be blocked by APV; the other may be mediated by low-threshold calcium channels and can be blocked by Ni2+.

Notes: Abstract Injections of WGA-HRP were made within the C1 segment of spinal cord in cats with a midsagittal section of the midbrain. A small number of labelled cells were found in the latero-caudal part of the deeper layers of the superior colliclus (SC) ipsilateral to the injection sites. Because of the complete section of the dorsal tegmental decussation, these results definitively demonstrate the existence of an ipsilateral tecto-spinal pathway projecting to upper cervical segments in the cat. Ipsilaterally projecting tecto-reticulo-spinal neurons represent about 5% of the total population of tectospinal neurons. They were exclusively located in the deeper collicular layers and most of them were found in the latero-caudal part of the SC. Comparison with our previous studies suggests that more ipsilateral tectospinal projections that found after the section of the dorsal tegmental decussation probably exist. They may arise from tecto-reticulo-spinal neurons recrossing the midline in the brainstem or in the rostral part of C1. By analogy with the cortico-spinal tract, we suggest that the existence of an ipsilateral tecto-spinal pathway can be regarded as evidence for a substantial development of the cat tecto-spinal system as compared with other mammals.

Notes: Abstract Single unit activities were recorded in Forel's field H (FFH) at the mesodiencephalic junction during orienting head movements in two alert cats under headfree conditions. Recordings were made of 63 neurons of which 20 showed phasic firing that preceded the onset of head movements by 20–100 ms and was temporally related to the dynamic phase of the orienting head movement. Nineteen of these neurons showed a preference for upward movements, while the remaining neuron preferred downward movements. Activities during orienting movements in eight different directions (each separated by 45°) were systematically analyzed for 12 of the 19 upward-preferring neurons. The activities were broadly tuned; in most of the neurons, maximum activity was observed for direct upward movements (+90°), but significant activity was also observed for ipsilateral and contralateral oblique upward movements (+45° and +135°). In these cases, the increase in activity preceded the onset of the movement. Some increase in activity was also observed for ipsilateral and contralateral horizontal, oblique downward and downward movements. However, the increase in activity in the latter cases occurred simultaneously with or lagged behind the onset of the movement and was often preceded by a decrease in activity. The same pattern of directional tuning was observed in the EMG of the biventer cervicis muscle, a target of FFH neurons. The preferred directions of the 12 upward-preferring neurons were estimated by calculating the vector sum of the activity and were distributed between +68° and +108°. The same amount of activity was observed for ipsilateral and contralateral oblique upward movements, suggesting that FFH neurons on both sides of the brainstem are equally activated even during oblique orienting. Input from the ipsilateral superior colliculus was investigated in 18 neurons, all of which were orthodromically activated with a latency of 0.8–1.8 ms, suggestive of a mono- or disynaptic excitatory connection. Seven neurons were identified as descending projection neurons by antidromic activation from the ipsilateral medullary reticular formation. Repetitive microstimulation of unilateral FFH induced oblique upward head movements and an accompanying torsional component, while simultaneous bilateral stimulation at comparable stimulus strength induced purely upward head movements. These results strongly suggest that the vertical component of orienting head movements is encoded by equal bilateral activation of the FFH.

Notes: Abstract The thalamic reticular nucleus (RTN) exerts an inhibitory influence upon the dorsal thalamus. During wakefulness and arousal, RTN neurons fire tonically, whereas during slow-wave sleep they fire rhythmic high frequency bursts. The effects produced by RTN inhibition upon the activity of dorsal thalamic neurons will therefore vary in relation to the firing mode of the RTN neurons. In the present study, we compared the effects of oscillating RTN neurons and of RTN neurons tonically activated with glutamate on the response profiles of single units reacting to controlled cutaneous stimulation in cat ventroposterior lateral thalamic nucleus (VPL). Experiments were performed under light barbiturate anesthesia and prior to the glutamate activation of the RTN, both RTN and VPL neurons showed spontaneous bursting patterns of activity consistent with the oscillatory mode. Typically, a cutaneous stimulus evoked a short latency excitatory response in VPL followed by a period of complete inhibition termed post-stimulus inhibition (PSI). In many neurons, the PSI was followed by a period of increased activity termed post-inhibitory excitation (PIE). Ejection of glutamate in the identified somatosensory division of the RTN shifted the oscillatory firing of its neurons to a high tonic mode and usually resulted in a decrease in VPL neuronal activity. Significant variations were observed in the occurrence and the magnitude of the effects among the different components of neuronal activity examined. Tonic activation of the RTN resulted in a significant reduction of ON- and OFF-PIEs in 81% of cases (30/37) and of spontaneous activity in 67% (22/ 33). In contrast, the response to a cutaneous stimulus was decreased in only 29% of cases (17/59) and was significantly increased in 24% (14/59). Tonic activation of the RTN by glutamate resulted in little change in the firing pattern of VPL neurons, and both short and long spike intervals were affected in a similar proportion. We conclude that the components of VPL neuronal activity most affected by switching RTN neurons from the oscillatory to the tonic mode are those normally dependent upon RTN neuronal oscillation. The present results also suggest that lowering background activity, such as occurs during the transition from sleep to wakefulness, is a factor leading to increase in the responsiveness of dorsal thalamic neurons.

Notes: Abstract The active length-tension curves of identified single motor units (MUs) belonging to peroneus longus muscle (PL) of anaesthetized adult cats were obtained by eliciting isometric single twitches and tetani. The recorded responses were evaluated by measuring the peak tension amplitude and the tension-time area at muscle lengths extending throughout the physiological length range of the muscle (mean 5.5 mm, standard deviation ±0.8). The muscle lengths at which each tested MU developed its maximal twitch (L tw) and tetanic (L te) tensions were determined and compared with the muscle length (L o) at which the stimulation of all the α-axons, innervating PL and contained in L7 ventral root, developed their maximal twitch tension. The mean of single MU L tw values was at L o+1.08±1.1 mm. Slow MUs showed the longest values of L tw(L o+1.6±1.0 mm). Single MUs stimulated at tetanic frequencies presented their L te at values shorter than L o (L o−2.8±1.7 mm). Slow MUs had the shortest L te (L o−3.4±1.5 mm). For all the units L te was shorter than L tw. L tw and L te were, respectively, negatively and positively correlated with the developed tension. Optimal length values also appeared to be related to the MU types. The possibility is discussed that the muscle and tendon compliances and the high non-linearities to the applied forces are the main factors which can determine the differences among L o, L tw and L te values. The relationships between MU type and optimal length values are suggested to be, at least partly, an epiphenomenon due to the different contraction strengths of the various MU types. However, the heterogeneous distribution of the MU types is brought into account to explain the dependence of L tw and L te values on MU type.

Notes: Abstract The purpose of this study was to examine the effect of prior experience concerning direction of a postural perturbation on the balance response of cats to translations of their support surface. Previous work has shown that, when cats are translated in many directions in the horizontal plane, they respond by exerting active forces with each paw in only two directions, termed the force constraint strategy. This study examined whether the force constraint strategy could be modified based on predictability of the direction of translation and whether this strategy is used by the naive animal with no prior experience of platform translation. Four cats were trained to stand quietly on the force platform using positive reinforcement, and then were implanted with chronically indwelling electrodes for recording electromyographic (EMG) activity. The first experiment concerned the response of the naive cats to their first exposure to platform translation and consisted of translations presented randomly in four different directions in the horizontal plane. The second experiment consisted of two complete sets of 16 directions of translation (15 trials per direction), with the direction of translation randomized in one set and serially ordered in the other, to make the direction of translation unpredictable or predictable, respectively. Forces exerted by the cat, EMG activity, and platform position were recorded during the 1-s trials. The use of the force constraint strategy was independent of prior experience with direction of translation, as was the amplitude of the response. Moreover, this strategy was observed in the naive cat. These findings suggest that the force constraint is a robust and consistent response to translational perturbations of stance in the cat and is part of its natural behavioral repertoire. The accuracy in specification of the direction of a postural response must be based on the sensory information that is obtained within a very short time after the onset of platform acceleration (loop time 40–70 ms). On the other hand, the amplitude of the postural response tended to decrease with experience and practice, suggesting a long-term change in central set that may manifest as a reduction in sensorimotor gain.

Notes: Abstract Extracellular microelectrode recordings were made from single cells of the lateral cervical nucleus (LCN) in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. The cells were tested for antidromic activation from the contralateral medial lemniscus and the contralateral tectum. Seventytwo LCN units were recorded which projected to one or both targets. Sixty (83%) projected through the medial lemniscus, and of these 36 (50% of the total) also projected to the tectum, whereas 24 (33%) projected through the medial lemniscus only; 12 (17%) projected only to the tectum. Twenty-nine units (40%) were excited by moving hairs of the coat but not by pinch of the skin, and 9 (31%) of these projected to the tectum, 11 (38%) through the medial lemniscus and 9 (31%) to both targets. Forty units (56%) were excited by hair movement and noxious pinch, and 3 (7%) of these projected to the tectum, 10 (25%) through the medial lemniscus and 27 (68%) to both targets. Three units (4%) had no discernible receptive fields and they all projected through the medial lemniscus, but not to the tectum. Of the 12 units projecting only to the tectum, 11 had receptive fields completely or partially on the trunk. Units projecting either through the medial lemniscus only, or through the medial lemniscus and also into the tectum, had receptive fields more widely distributed: these included small fields on the fore- and hind feet, on the limbs and also, a minority, on the trunk. Units with glove- or stocking-like receptive fields projected through the medial lemniscus. The results show that while most LCN cells project through the medial lemniscus, those excited by hair movement alone preferentially project either to the tectum or through the medial lemniscus, but not by both routes. The differences in receptive field properties of the differently projecting units are discussed in terms of the possible functions of the spinocervical system.

Notes: Abstract Intracortical inhibition is believed to enhance the orientation tuning of striate cortical neurons, but the origin of this inhibition is unclear. To examine the possible influence of ascending inhibitory projections from the infragranular layers of striate cortex on the orientation selectivity of neurons in the supragranular layers, we measured the spatiotemporal response properties of 32 supragranular neurons in the cat before, during, and after neural activity in the infragranular layers beneath the recorded cells was inactivated by iontophoretic administration of GABA. During GABA iontophoresis, the orientation tuning bandwidth of 15 (46.9%) supragranular neurons broadened as a result of increases in response amplitude to stimuli oriented about ±20° away from the preferred stimulus angle. The mean (±SD) baseline orientation tuning bandwidth (half width at half height) of these neurons was 13.08±2.3°. Their mean tuning bandwidth during inactivation of the infragranular layers increased to 19.59±2.54°, an increase of 49.7%. The mean percentage increase in orientation tuning bandwidth of the individual neurons was 47.4%. Four neurons exhibited symmetrical changes in their orientation tuning functions, while 11 neurons displayed asymmetrical changes. The change in form of the orientation tuning functions appeared to depend on the relative vertical alignment of the recorded neuron and the infragranular region of inactivation. Neurons located in close vertical register with the inactivated infragranular tissue exhibited symmetric changes in their orientation tuning functions. The neurons exhibiting asymmetric changes in their orientation tuning functions were located just outside the vertical register. Eight of these 11 neurons also demonstrated a mean shift of 6.67±5.77° in their preferred stimulus orientation. The magnitude of change in the orientation tuning functions increased as the delivery of GABA was prolonged. Responses returned to normal approximately 30 min after the delivery of GABA was discontinued. We conclude that inhibitory projections from neurons within the infragranular layers of striate cortex in cats can enhance the orientation selectivity of supragranular striate cortical neurons.

Notes: Abstract Neuronal responses to hairy skin stimulation were simultaneously recorded in the ventral posterolateral nucleus (VPL) of the thalamus and primary somatosensory cortex (SI) of halothane-anesthetized cats. Among 233 thalamocortical neuron pairs, cross-correlation analysis revealed significant interactions in 120 pairs. Excitatory interactions were most prevalent and included influences occurring exclusively in the thalamocortical (41 pairs) or corticothalamic (23 pairs) directions as well as multiphasic interactions (40 pairs) in both directions. Only 16 pairs exhibited inhibitory interactions and 7 of these involved multiphasic combinations of excitation and inhibition. In 14 of these neuron pairs, inhibition was exerted in the corticothalamic direction. Receptive field (RF) overlap between thalamic and cortical neurons varied considerably, and neuronal interactions were more likely for neuron pairs sharing large portions of their combined RFs. Computer-controlled stimulation was delivered to multiple RF sites but only 46% of the neuron pairs displayed interactions at more than one stimulation site and only four neuron pairs showed interactions at all stimulus positions. When interactions occurred at multiple stimulus sites, 40% of these interactions were characterized by timing shifts where the time interval between VPL and SI discharges varied as much as 20 ms because of stimulus relocation. In nine neuron pairs, systematic shifts in stimulus position produced reversals in the temporal sequence of thalamic and cortical neuronal discharges. Functional interactions between thalamic and cortical neurons were detected during both spontaneous and stimulus-induced activity. Matched-sample comparisons of connection strength and half-widths of thalamocortical peaks during spontaneous and stimulus-induced activity indicated that functional interactions produced by cutaneous stimulation were significantly stronger and had less temporal variability than those occurring spontaneously.

Notes: Abstract Peripheral input to spino-cervical tract (SCT) neurons located in the L4 and L5 segments of the cat spinal cord was investigated using both extracellular and intracellular recording. The main aim was to find out whether midlumbar SCT neurons are excited monosynaptically not only by cutaneous afferents but also by group II muscle afferents, as in the sacral segments but apparently not in the caudal lumbar segments. Input from group II muscle afferents was found in 73% of investigated neurons; the latencies of excitation by group II afferents were compatible with a monosynaptic coupling between these afferents and 62% of neurons. The majority of the midlumbar SCT neurons were excited by group II afferents of the quadriceps and deep peroneal nerves. The predominant monosynaptic input from cutaneous afferents to the same neurons was from the saphenous nerve.

Notes: Abstract The axonal projections of 62 posterior canal (PC)-activated excitatory and inhibitory secondary vestibular neurons were studied electrophysiologically in cats. PC-related neurons were identified by monosynaptic activation elicited by electrical stimulation of the vestibular nerve and activation following nose-up rotation of the animal's head. Single excitatory and inhibitory neurons were identified by antidromic activation following electrical stimulation of the contralateral and ipsilateral medial longitudinal fasciculus, respectively. The oculomotor projections of identified neurons were confirmed with a spike-triggered averaging technique. The axonal projections of the identified neurons were then studied by systematic, antidromic stimulation of the mesodiencephalon. Excitatory neurons showed two main types of axonal projections. In one type, axonal branches were issued to the interstitial nucleus of Cajal, central gray, and thalamus including the ventral posterolateral, ventral posteromedial, ventral lateral, ventral medial, centromedian, central lateral, lateral posterior, and ventral lateral geniculate nuclei. The other type was more frequently observed, giving off axon collaterals to the above-mentioned regions and to Forel's field H as well. Inhibitory neurons issued axonal branches to limited areas which included the central gray, interstitial nucleus of Cajal, its adjacent reticular formation and caudalmost part of Forel's field H, but not the rostral part of the Forel's field H and the thalamus. These results suggest that PC-related excitatory neurons participate in the genesis of vertical eye movements and in the perception of the vestibular sensation, and that PC-related inhibitory neurons seem to take part only in the genesis of vertical eye movements.

Notes: Abstract The spike activity of perigeniculate cells evoked by small light spots flashing along the axes of their receptive fields was recorded and presented in response planes. This method allowed the investigated neurons to be grouped into two classes characterized by (1) large receptive fields and phasic-like responses and (2) small fields and tonic responses. The latency measurements for stimulation of the optic chiasma and visual cortex revealed that the cells from the first group are excited by fast, Y fibers and the second by slow, X axons. The spatial tuning curves of the second harmonic component, as measured from the responses of the cells from the two groups for slowly moving square gratings, are also different. We conclude that the X and Y systems of the visual pathway are segregated at the level of the perigeniculate nucleus.

Notes: Abstract Lumbar motoneurones were recorded intracellularly during fictive locomotion induced by stimulation of the mesencephalic locomotor region in decerebrate cats. After blocking the action potentials using intracellular QX-314, and by using a discontinuous current clamp, it is shown that the excitatory component of the locomotor drive potentials behaves in a voltage-dependent manner, such that its amplitude increases with depolarisation. As the input to motoneurones during locomotion is comprised of alternating excitation and inhibition, it was desirable to examine the excitatory input in relative isolation. This was accomplished in spinalised decerebrate cats treated with nialamide and l-dihydroxy-phenylalanine (l-DOPA) by studying the excitatory post-synaptic potentials (EPSPs) evoked from the “flexor reflex afferents” (FRA) and extensor Ib afferents, both of which are likely to be mediated via the locomotor network. As expected, these EPSPs also demonstrate a voltage-dependent increase in amplitude. In addition, the input to motoneurones from the network for scratching, which is thought to share interneurones with the locomotor network, also results in voltage-dependent excitation. The possible underlying mechanisms of NMDA-mediated excitation and plateau potentials are discussed:both may contribute to the observed effect. It is suggested that this nonlinear increase in excitation contributes to the mechanisms involved in the production of the high rates of repetitive firing of motoneurones typically seen during locomotion, thus ensuring appropriate muscle contraction.

Notes: Abstract In the context of an analysis concerning factors of importance for the relative contributions of recruitment and rate gradation of muscle force, the distribution of electrical excitability was analyzed for medial gastrocnemius (MG) motoneurones of rat and cat. The experimental data came from previously collected intracellular measurements in animals anaesthetized with pentobarbitone. Electrical excitability was measured as the threshold (nanoamperes) for single spike generation (rheobase) in rat and for maintained repetitive firing (rhythmic threshold) in cat. Furthermore, the data included measurements of axonal conduction velocity and of contractile properties of the muscle units innervated by the studied motoneurones. The units were categorized into types S (slow-twitch, fatigue-resistant), FR (fast-twitch, fatigue-resistant) and FF (fast-twitch, fatiguable) on the basis of the combined criteria of twitch-speed and sensitivity to fatigue. We confirmed that, in spite of the presence of normal-looking symmetrical distributions of axonal conduction velocity, there was a positive skew in the distribution of electrical excitability (relatively high numbers of cells with low thresholds, few with high ones). Within each unit category (S, FR, FF), we ranked the motoneurones according to their relative electrical excitability and calculated the threshold difference between consecutive cells (“threshold spacing”). In accordance with the skewed distribution of electrical excitability, we found that the mean threshold spacing was ranked in the same way as the mean thresholds, i.e. S〈FR〈FF; the statistical analysis showed that, for cats as well as rats, small threshold-spacing steps were significantly more common for S than for FF motoneurones. In the discussion it is pointed out that the narrow threshold-spacing for S units, as compared to FF units, would tend to decrease the relative amount of recruitment-parallel rate modulation in these cells. Thus, the spacing of recruitment thresholds tends to allow the easily recruited S motoneurones to remain firing at relatively low rates during ongoing recruitment gradation, which would be of potential value in promoting a high degree of endurance for long-lasting postural contractions.

Notes: Abstract The present paper describes a new method using computerised image analysis techniques for quantification of tracer extravasation over the blood-brain barrier as studied by intravital fluorescence microscopy. Cats were equipped with an open cranial window and continuously infused with fluorescein isothiocyanate-labelled dextran (FITC-dextran, mol. wt. 70 000) to maintain a steady plasma concentration. Several cortical fields were recorded in each experiment and the images stored on video tape for off-line analysis. This procedure, which largely eliminates the superficial pial vasculature and allows extraction of the extravasation areas, consists of the following steps: (1) averaging of images, (2) software shading correction based on the original images for compensation of optical non-uniformity, (3) correction of displacement artefacts, (4) intensity adjustment, (5) generation of subtraction images by subtracting the first image of a series from the subsequent ones, (6) median filtering and thresholding, (7) a length recognition algorithm, and (8) elimination of small areas. Compared to the previously described method, step (2) has been newly developed and steps (4) and (8) added to enhance sensitivity for detecting tracer extravasation. The degree of extravasation in a cortical field at a given time point [E(f) value] was calculated as the mean intensity of the remaining pixels. TheE(f) is a quantitative value computed by a fully automatised procedure which takes into account the number, as well as the size and intensity, of extravasation areas in a given cortical field. TheE(f) values obtained at different times in a series of experiments were averaged to give theE(I) value. TheE(I) value did not alter when hypercapnia was employed to induce pure vasodilatation. On the other hand it increased dramatically, indicating tracer extravasation, during topical application of high concentrations of adenosine (10−5–10−3 M). The new computerised image analysis procedure may therefore be suitable for measuring quantitatively tracer extravasation over the blood-brain barrier in vivo under different experimental conditions. It may also be applicable to study changes of vascular permeability in peripheral vascular beds.

Notes: Abstract Bladder wall mechanoreceptors are essential elements in micturition and continence reflexes. While they have been described as tension receptors, their response to bladder wall deformation has always been characterised in terms of pressure. The firing patterns of 10 bladder wall mechanoreceptors were determined during bladder distensions at a natural and a much faster rate. In all units firing rate was higher at any given pressure at the slower bladder distension rate. This inverse rate dependence was reduced when firing rate was related to a derived measure of bladder wall tension and abolished when multi-fibre recordings were used. We conclude that it is important to incorporate volume effects in studies of continence control systems.

Notes: Abstract Using an X-ray television system, we measured directly changes in the internal diameter (ID), flow velocity, and volume flow of the small pulmonary vessels (100–500 μm ID) in response to electrical sympathetic nerve stimulation (SNS) in anaesthetized cats before and after adrenergic receptor blockade. Flow velocity was obtained by measuring the distance that the leading edge of the contrast medium moved per 0.1 s in the small arteries. Volume flow was obtained from the product of flow velocity and cross-sectional area calculated from the ID of the small arteries. SNS was accolmplished with 10- to 15-V square-wave pulses of 2-ms duration at 20–30 Hz for 20-s periods. In response to SNS, arterial ID decreased significantly by 8–13% in the 200- to 500-μm vessels but not in the 100- to 200-μm vessels. In the veins, on the other hand, there was no significant ID decrease in any of the 100- to 500-μm vessels. After α-receptor blockade (phentolamine, 2 mg/kg i.V.), there were significant ID increases (4–9%) in the 100- to 500-μm arteries in response to SNS, the maximum increases being in the 100- to 200-μm arteries. After β-blockade (propranolol, 2 mg/kg i.V.), the ID decrease due to SNS in the 200- to 500-μm arteries was enhanced (24–27%) and, in addition, the 100- to 200-μm arteries exhibited a significant ID decrease (18%). Combined α and β-blockade completely abolished the ID decrease due to SNS. In the veins, on the other hand, no ID change occurred even after α- or β-blockade. The results indicate that SNS selectively constricts 200- to 500-μm arteries. The data suggests that SNS has α-mediated vasoconstrictor and β-mediated vasodilator effects on the 100- to 500-μm arteries and that the ID response pattern to SNS depends chiefly on the balance between α-mediated vasoconstriction and β-mediated vasodilation. Associated with the ID decrease due to SNS, flow velocity was increased by 21%. However, SNS did not affect volume flow, because the increase in velocity was compensated by the reduction in the cross-sectional area (due to the decreased ID).

Notes: Abstract Autonomic innervation of the tongue was investigated in cats using the horseradish peroxidase retrograde tracing method. The tongue was found to be innervated by sympathetic fibers originating in the ipsilateral superior cervical ganglion, but not by those originating in the middle cervical ganglion or stellate ganglion. The tongue was also innervated by fibers originating in the ipsilateral pterygopalatine ganglion, suggesting that this innervation is parasympathetic.

Notes: Abstract The distribution of mitochondria, their content and concentration (expressed as the ratio of the mean volume of mitochondria and the surface of the sensory axon) were determined in group-III and-IV nerve fibres innervating the knee joint capsule in the cat. Mitochondria mainly accumulated in axonal swellings (“beads”) and end bulbs of the terminal branches. Between single nerve fibres, marked differences in the content and the concentration of mitochondria were obtained in proximal portions (inside of the perineurium) and in distal portions (unmyelinated sensory endings). In group-III nerve fibres, the mitochondrial concentration ranged from 0.005 to 0.030 μm3/μm2 (proximal portion) and from 0.016 to 0.080 μm3/μm2 (distal portion). In unmyelinated group-IV nerve fibres, the values also showed a broad variation ranging from 0.001 to 0.011 μm3/μm2 (proximal portion) and from 0.003 to 0.019 μm3/μm2 (distal portion). The wide range of mitochondrial concentrations may reflect different energy consumption during receptive processes: nerve fibres with a low mechanical threshold and a high probability of excitatory events may be rich in mitochondria, whereas fibres with a high mechanical threshold and a low probability of excitatory events may be poor in mitochondria.

Notes: Abstract An immunohistochemical study of the cat pineal gland was performed using a rabbit polyclonal antibody directed against neuropeptide Y (NPY) and an antibody directed against the C-terminal flanking peptide of neuropeptide Y (CPON). Numerous NPY- and CPON-immunoreactive (IR) nerve fibers were demonstrated throughout the gland and in the pineal capsule. The number of IR nerve fibers in the capsule was high and from this location fibers were observed to penetrate into the gland proper via the pineal connective tissue septa, often following the blood vessels. From the connective tissue septa IR fibers intruded into the parenchyma between the pinealocytes. Many IR nerve fibers were observed in the pineal stalk and in the habenular as well as the posterior commissural areas. The number of NPY/CPON-IR nerve fibers in pineal glands from animals bilaterally ganglionectomized two weeks before sacrifice was low. The source of most of the extrasympathetic NPY/CPONergic nerve fibers is probably the brain from where they enter the pineal via the pineal stalk. However, an origin of some of the fibers from parasympathetic ganglia cannot be excluded due to the presence of a few IR fibers in the pineal capsule of ganglionectomized animals. It is concluded that the cat pineal is richly innervated with NPYergic nerve fibers mostly of sympathetic origin. The posttranslational processing of the NPY promolecule results in the presence of both NPY and CPON in intrapineal nerve fibers.

Notes: Abstract The distributions of neuronal nitric oxide synthase immunoreactivity (NOS-IR) and NADPH-diaphorase (NADPH-d) activity were compared in the cat spinal cord. NOS-IR in neurons around the central canal, in superficial laminae (I and II) of the dorsal horn, in the dorsal commissure, and in fibers in the superficial dorsal horn was observed at all levels of the spinal cord. In these regions, NOS-IR paralleled NADPH-d activity. The sympathetic autonomic nucleus in the rostral lumbar and thoracic segments exhibited prominent NOS-IR and NADPH-d activity, whereas the parasympathetic nucleus in the sacral segments did not exhibit NOS-IR or NADPH-d activity. Within the region of the sympathetic autonomic nucleus, fewer NOS-IR cells were identified compared with NADPH-d cells. The most prominent NADPH-d activity in the sacral segments occurred in fibers within and extending from Lissauer's tract in laminae I and V along the lateral edge of the dorsal horn to the region of the sacral parasympathetic nucleus. These afferent projections did not exhibit NOS-IR; however, NOS-IR and NADPH-d activity were demonstrated in dorsal root ganglion cells (L7-S2). The results of this study demonstrate that NADPH-d activity is not always a specific histochemical marker for NO-containing neural structures.

Notes: Abstract The performance of a prototype AVL MS8 VET impedance haematology analyser was compared with that of a Technicon H*1 flow cytometry haematology analyser using blood from dogs and cats. Analysis was performed with the AVL MS8 VET on the day of blood collection and with the Technicon H*1 on the following day. Differences were noted in feline leucocyte and platelet counts and in canine and feline mean cell volume and mean cell haemoglobin concentration between analyses. The results indicate that the AVL MS8 VET is a reliable analyser for blood samples from dogs but may not be for those from cats. Attention is drawn to the importance of considering the type of analyser, calibration of the analyser, time of analysis after blood collection (effect of postal delay) and the effect of anticoagulants.

Notes: Abstract. The distributions of neuronal nitric oxide synthase immunoreactivity (NOS-IR) and NADPH-diaphorase (NADPH-d) activity were compared in the cat spinal cord. NOS-IR in neurons around the central canal, in superficial laminae (I and II) of the dorsal horn, in the dorsal commissure, and in fibers in the superficial dorsal horn was observed at all levels of the spinal cord. In these regions, NOS-IR paralleled NADPH-d activity. The sympathetic autonomic nucleus in the rostral lumbar and thoracic segments exhibited prominent NOS-IR and NADPH-d activity, whereas the parasympathetic nucleus in the sacral segments did not exhibit NOS-IR or NADPH-d activity. Within the region of the sympathetic autonomic nucleus, fewer NOS-IR cells were identified compared with NADPH-d cells. The most prominent NADPH-d activity in the sacral segments occurred in fibers within and extending from Lissauer's tract in laminae I and V along the lateral edge of the dorsal horn to the region of the sacral parasympathetic nucleus. These afferent projections did not exhibit NOS-IR; however, NOS-IR and NADPH-d activity were demonstrated in dorsal root ganglion cells (L7-S2). The results of this study demonstrate that NADPH-d activity is not always a specific histochemical marker for NO-containing neural structures.

Notes: This study explores the organization of the striatal projections from the rostral caudate nucleus to the output nuclei of the basal ganglia in the cat. Tracer deposits were stereotaxically injected in different dorsoventral, mediolateral, and rostrocaudal sectors of the head of the caudate nucleus using horseradish peroxidase (HRP) conjugated with wheat germ agglutinin (HRP-WGA) either alone or mixed with free HRP. After the injections, a detailed analysis of the terminal labeling was carried out within the globus pallidus (GP), the entopeduncular nucleus (Ep), and the substantia nigra (SN) pars reticulata (SNR). Our findings illustrate how different dorsoventral, mediolateral, and rostrocaudal parts of the rostral caudate nucleus project primarily to similarly positioned but spatially segregated parts of GP. The striatoentopeduncular pathway was also organized topographically, but there was overlapping by projections from different parts of the rostral caudate nucleus. Areas of topographical segregation and zones of overlap were detected in the organization of the striatal projections from the rostral caudate nucleus to SNR. These results raise the possibility of distinct striatal actions upon different sectors of the output nuclei of the basal ganglia and, indirectly, upon their targets in the thalamus and brainstem. © 1994 Wiley-Liss, Inc.

Notes: Abstract The present study describes substance P-like immunoreactivity in the ciliary ganglia of monkey (Macaca fascicularis) and cat. About 60% of neurons in the monkey ciliary ganglion and 40% in the cat ciliary ganglion were substance P-like immunoreactive, ranging from faint to moderate staining. Substance P-like immunoreactivity was located in cell bodies, dendritic profiles and axons. In the monkey, substance P-like immunoreactive pericellular arborisations were associated with about 0.5%–3% of the ganglion cells, which were either negatively, faintly or moderately stained. An electron-microscopic study demonstrated the presence of either substance P-like immunoreactive positive or negative axon terminals synapsing or closely associated with positive dendritic profiles in both the monkey and cat ciliary ganglia. The results suggest that substance P plays an important role in the ciliary ganglion, perhaps as a modulator or transmitter.

Notes: Abstract. Levels of interphotoreceptor retinoid-binding protein (IRBP) protein and message in retinas of Abyssinian cats homozygous for progressive rod-cone degeneration were determined at early ages, well before the onset of clinical retinal degeneration. IRBP gene expression was assessed by immunochemical quantitation of IRBP protein, and by Northern blotting and slot-blotting of total RNA using a human IRBP cDNA probe. Morphology was assessed by electron microscopy and immunocytochemistry. Levels of both IRBP protein and message in affected Abyssinian cat retinas were significantly reduced below normal as early as 4 weeks of age at the earliest stage of retinal disorientation. Opsin mRNA was more abundant in affected Abyssininian cat retinas than in control retinas. This was at least 1 year before the onset of clinical symptoms. The reduction in IRBP gene expression to levels significantly below normal well before the onset of retinal degeneration in affected Abyssinian cat retinas indicates that this represents a primary defect or at least an early problem that could itself cause adverse effects.

Notes: Abstract The effects of permanent focal cerebral ischaemia on Alz-50 and ubiquitin antibody immunohistochemical staining were investigated in vivo in the cat. Alz-50 and ubiquitin antibody staining was compared to the distribution of ischaemic cell damage. Six hours following permanent occlusion of one middle cerebral artery, Alz-50 immunoreactivity was present in neurones in the ipsilateral ischaemic cerebral cortex and caudate nucleus but not in any region of the contralateral hemisphere or in sham-operated cats. Only a proportion of neurones were stained with Alz-50 and these did not have the shrunken, pyknotic appearance characteristic of irreversible ischaemic cell damage. Ubiquitin immunoreactivity was also increased in the ischaemic hemisphere, again only a proportion of neurones were stained. The Alz-50 antibody recognises the microtubule-associated protein tau and stains neurofibrillary tangles as well as neurones vulnerable to neurofibrillary change in tissue sections of Alzheimer brain. The results indicate that there are changes in tau protein in response to an ischaemic insult, but only in some neurones, which may reflect an early stage of the degenerative process. Increased ubiquitin immunoreactivity may be a response to the presence of abnormal proteins, including tau, which are induced by an ischaemic challenge.

Notes: Abstract The ciliary ganglia of eight healthy adult cats were studied by light and electron microscopy. The ganglion, measuring about 2 mm in length, was consistently found to be attached to the branch from the oculomotor nerve supplying the inferior oblique muscle. The number of neurons varied from 2773 to 3794 after applying Abercrombie's correction. The mean of average somal diameter of the neurons was 36.5 μm (SD = 5.0 μm) and the mean of somal cross-sectional area was 904.2 μm2 (SD = 262.8 μm2). The mean of average nuclear diameter was 13.9 urn (SD = 1.8 μm) and the mean of nuclear cross-sectional area was 142.2 μm2 (SD = 37.1 μm2). The mean of the aspect ratios of the soma and nucleus were 1.2 (SD = 0.1) and 1.1 (SD = 0.1) respectively. The frequency distributions of these parameters were all unimodal. Under the light microscope, the Nissl granules in the neurons were prominent and were distributed peripherally, perinuclearly or randomly in the cytoplasm. Under the electron microscope, the rough endoplasmic reticulum showed a similar pattern of distribution in the cytoplasm. In some neurons, glycogen-like granules were present; these were either distributed randomly throughout the cell, or aligned in single rows in relation to sub-surface cisterns and between the cisterns of smooth and rough endoplasmic reticulum. Most of the dendrites were short protrusions from the cell body; some contained glycogen-like granules. Occasionally, the dendritic protrusions were electron-dense. All the synapses encountered were axodendritic. In most axon terminals, the synaptic vesicles were spherical and measured 30–50 nm in diameter; in some, they were flattened, measuring 50 nm by 20 nm. Some axon terminals containing either spherical or flattened synaptic vesicles also contained large dense-cored vesicles that measured 80–100 nm, while their dense core measured 40–60 nm.

Notes: Abstract Intrinsic connections in the cat primary auditory field (AI) as revealed by injections Phaseolus vulgaris leucoagglutinin (PHA-L) or biocytin, had an anisotropic and patchy distribution. Neurons, labelled retrogradely with PHA-L were concentrated along a dorsoventral stripe through the injection site and rostral to it; the spread of rostrally located neurons was greater after injections into regions of low rather than high characteristic frequencies. The intensity of retrograde labelling varied from weak and granular to very strong and Golgi-like. Out of 313 Golgi like retrogradely labelled neurons 79.6% were pyramidal, 17.2% multipolar, 2.6% bipolar, and 0.6% bitufted; 13.4% were putatively inhibitory, i.e. aspiny or sparsely spiny multipolar, or bitufted. Individual anterogradely labelled intrinsic axons were reconstructed for distances of 2 to 7 mm. Five main types were distinguished on the basis of the branching pattern and the location of synaptic specialisations. Type 1 axons travelled horizontally within layers II to VI and sent collaterals at regular intervals; boutons were only present in the terminal arborizations of these collaterals. Type 2 axons also travelled horizontally within layers II to VI and had rather short and thin collateral branches; boutons or spine-like protrusions occurred in most parts of the axon. Type 3 axons travelled obliquely through the cortex and formed a single terminal arborization, the only site where boutons were found. Type 4 axons travelled for some distance in layer I; they formed a heterogeneous group as to their collaterals and synaptic specializations. Type 5 axons travelled at the interface between layer VI and the white matter; boutons en passant, spine-like protrusions, and thin short branches with boutons en passant were frequent all along their trajectory. Thus, only some axonal types sustain the patchy pattern of intrinsic connectivity, whereas others are involved in a more diffuse connectivity.

Notes: Abstract The motoneurons (MNs) in the ventrolateral nucleus (VLN) of the upper sacral spinal cord segments in the cat supply the external sphincters and the ischiocavernosii muscles. The dendrites of the MNs in the VLN are arranged into rostro-caudally oriented bundles (ventrolateral dendritic bundle, VLB). In this study we describe the distribution and synaptic arrangement of γ-aminobutyric acid-immunoreactive (GABA-IR) axonal bouton profiles innervating the VLB. This was accomplished using the peroxidase-antiperoxidase technique and a polyclonal antibody raised against glutaraldehydeconjugated GABA. The VLN receives an extensive innervation of GABAIR axonal bouton profiles that surround both cell bodies and dendrites. Twenty-five per cent of the total number of vesicle-containing axonal profiles in the VLN neuropil were estimated to be GABA-IR. On cell bodies in the α-motoneuron size-range, the membrane covering of GABA-IR bouton profiles was about 18% and they constituted about 29% of the total membrane covering of axonal bouton profiles. Quantitative analysis of GABAIR bouton profiles on dendrites revealed membrane covering figures rather similar to those on the cell bodies. They were not randomly distributed within the dendritic arborisations. Instead, they were very infrequent (2.5% of the covering) on small calibre dendrites (〈 1 μm) as compared to larger dendrites (〉 1 μm, 14–18.5% of the covering), although the total membrane covering of axonal bouton profiles was rather similar for all dendrites (42–52%). The data on membrane covering by GABA-IR boutons presented here may be low estimates due to technical limitations, indicating that the GABAergic input to this region might be even more extensive. A frequent finding was that one and the same GABAIR bouton made synaptic contact with two to three adjacent dendrites. This type of synaptic arrangement among the VLN MNs indicates a divergence of the GABAergic input at the terminal level. In addition, the postsynaptic dendrites involved in such arrangements often disclosed dendro-dendritic contacts. In total, 44% of the bundled dendrites in the VLN disclosed direct dendro-dendritic contact regions. These contacts were most often of the puncta adherentia type, while desmosome-type contacts were less frequent. None of the dendro-dendritic contacts studied had the characteristics of a gap junction. Taken together, the present results indicate that GABA may be a transmitter substance in a large fraction of the synaptic input to the VLN MNs. Furthermore, the location of GABA-IR bouton profiles on the cell bodies and more proximal regions of the dendritic trees implies that they could exert a considerable influence on MN activity pattern.

Notes: Abstract The effects of electrical stimulation within the midbrain on fusimotor output to the jaw elevator muscles were studied in anaesthetized cats. Muscle spindle afferents recorded in the mesencephalic trigeminal nucleus were categorised as primary or secondary by their responses to succinylcholine during sinusoidal or rampand-hold stretches. Changes in their stretch responses during midbrain stimulation were then assessed by changes in bias and in dynamic sensitivity. Problems were encountered in interpreting changes in sine wave stretch responses of primary afferents, in some of which a very small change in firing pattern produced large changes in estimates of the reponse amplitude. Sine wave testing also sometimes over-estimated static effects and under-estimated dynamic effects relative to ramp responses. On other occasions a small amount of static fusimotor activity caused a marked increase in sine response amplitude, which could be wrongly interpreted as a dynamic effect. Consequently, ramp responses only were used for diagnosing fusimotor changes. The most effective region for producing pure dynamic fusimotor excitation was directly rostral to the red nucleus, extending dorsally and ventrally approximately in the course of the retroflex bundle. Stimulation of regions caudal and dorso-caudal to the red nucleus, previously designated as the mesencephalic area for dynamic fusimotor control of leg muscles, gave static or mixed static and dynamic effects on jaw spindles. The use of midbrain stimulation to identify fusimotor neurones of jaw muscles as static or dynamic would be most reliable with stimulation just rostral to the red nucleus and would require spindle afferent behaviour to be monitored at the same time with ramp stretches.

Notes: Abstract Forelimb movements and motor skills were studied in adult cats in order to determine the effect of brain damage inflicted at different postnatal ages. The unilateral lesion included the cortical areas from which the pyramidal tract originates in cat: areas 4 and 6 corresponding to the motor cortex; areas 3, 2 and 1 corresponding to the primary somatosensory cortex; and part of area 2 prae-insularis corresponding to the secondary somatosensory cortex. Forelimb performance of a food-retrieving task requiring proximal as well as distal muscles was assessed by comparing the limb contralateral to the damaged hemisphere (affected limb) with the limb contralateral to the intact hemisphere (non-affected limb) that appeared to perform the task as well as both limbs of control animals. In simple task-related movements, all operated animals were rapidly able to achieve the goal with the affected limb, whatever the age at lesion. In complex tasks, the ability to achieve the goal with the affected limb decreased with increasing age at lesion. Recovery of distal skills, i.e. grasping and wrist rotation, did not occur in animals operated on after the 23rd postnatal day (PND), and recovery of proximal skills, i.e. amplitude and precision of the reaching movement, did not occur in animals operated on after the 45th PND. The critical time for the recovery of distal skills lies somewhere between the 23rd and 30th PND, whereas for the recovery of proximal skills it lies somewhere between the 45th and 60th PND. These critical dates for the recovery of motor skills support the Kennard doctrine. Different critical times for proximal and distal skills may be explained in terms of different stages of sensorimotor development in kitten. It is hypothesised that recovery only occurs if brain damage is inflicted before maturation of the nervous system underlying a given motor skill.

Notes: Abstract In a previous study, we have shown that the corticofugal projection to the dLGN enhances inhibitory mechanisms underlying length tuning. This suggests that the inhibitory influences deriving from the corticofugal feedback should exhibit characteristics that reflect the response properties of orientation-tuned layer VI cells. Here we report data obtained from experiments using a bipartite visual stimulus, with an inner section over the dLGN cell receptive field centre and an outer section extending beyond it. For both X and Y cells there was a modulation of the strength of the surround antagonism of centre responses that was dependent on the orientation alignment of contours in the two components of the stimulus. Layer VI cells showed maximal responses when the two components were aligned to the same orientation; dLGN cells showed a minimal response. Varying the orientation alignment of the inner and outer components of the stimulus in a randomised, interleaved fashion showed that bringing the stimulus into alignment resulted in a 24.28% increase in the surround antagonism of the centre response. Blocking cortical activity showed this effect of alignment to be strongly dependent on corticofugal feedback. This effect of orientation alignment appears to apply for any absolute orientation of the alignment condition and supports the view that an entire subset of cortical orientation columns generate the feedback influencing any given dLGN cell. This mechanism makes dLGN cells sensitive to the orientation domain discontinuities in elongated contours moving across their receptive field.

Notes: Abstract The activity of tectoreticulospinal neurons (TRSN) during orienting gaze shifts was studied in alert, head-fixed cats by intra-axonal recordings. The scope of the study was to evaluate the role of this class of superior colliculus neurons in the generation of slow eye movements (drifts) which often follow main-sequence saccades and sometimes appear as an independent motor event of orienting. The parameters of such movements are described in the first part of the paper. The organization of underlying pathways in the lower brainstem has been studied by intra-axonal horseradish peroxidase (HRP) tracing. The mean amplitude of postsaccadic drifts (PSD) is 1.21° (SD 0.63), but it can eventually reach 6–8°. PSDs have mean velocity of 14.9°/s (SD 4.28) and mean duration of 104.2 ms (SD 50.8). These two parameters are positively correlated with PSD amplitude. The presence of PSDs is usually associated with an increased neck muscle activity on the side toward which the eyes move. The durations of these two motor events show a reliable positive correlation. PSDs appear to occur when gaze error persists after a saccade and a correction is attempted by means of a slow eye movement and a head turn. The durations of TRSN bursts are, on average, longer than the sum of the lead time and the saccade duration. Bursts associated with combinations of saccades and PSD are significantly longer than those recorded in the absence of PSDs. The probability of occurrence of PSDs is higher when firing of TRSNs continues after saccade termination. Such prolonged discharges usually coincide with a combination of PSDs and phasic activation of the neck electromyogram. The mean firing rate of TRSNs during PSDs is 62% of that during saccade-related portions of the burst and declines to 45% after the end of PSDs. According to its timing and intensity, postsaccadic firing of TRSNs is appropriate as a signal underlying slow, corrective eye movements and later portions of phasic neck muscle contractions during orienting. Intraaxonal HRP labeling showed that visuomotor TRSNs of the X type (n = 3) terminate in the abducens nucleus, with 145–331 boutons terminaux and en passant. Average bouton densities in the nucleus are lower than in the periabducens reticular formation, but higher than in more rostral paramedian pontine reticular formation (PPRF) regions. Terminal fields in the PPRF match the locations of “eye-neck” reticulospinal neurons (RSNs) and exitatory burst neurons. Termination densities comparable with those in the caudal PPRF are found also in the rostral nucleus reticularis gigantocellularis, which contains phasic RSNs (“neck bursters”) and inhibitory burst neurons. Morphological observations alone do not exclude firing rate modulation of abducens motoneurons through the monosynaptic tectal pathway. However, the available physiological data point to a major role of a multiple convergent connection involving the eye-neck RSNs. In conclusion, the signals of X type TRSNs, reinforced by parallel connection through RSNs, encode mainly the intended head movement. Collateral actions of these two populations may be sufficient to induce slow, orienting eye movements, independently of the burst output from the classic saccadic generator.

Notes: Abstract Focal blockade of restricted regions in layer V of area 18 was used to assess the contribution of this region to the responses to high-velocity stimuli of cells in retinotopically matched, layer V in area 17. In 40% of cases, blockade within area 18 revealed responses of area 17 cells to high-velocity stimuli to which they previously showed only poor responses. Stimulus specificity of the cells in area 17 was otherwise unaltered. All effects were reversible and repeatable. We suggest that a component of the output of layer V from area 18 normally suppresses the responses of retinotopically matched cells within area 17 to stimuli of high velocity, thereby enhancing the specificity of those cells to stimuli of low velocity

Notes: Abstract Trajectory formation of unrestrained forelimb target-reaching was investigated in six cats. A Selspotlike recording system was used for three-dimensional recording of the position of the wrist every 3 ms with the aid of two cameras detecting infrared light emitted from diodes taped to the wrist. These measurements allowed reconstruction of movement paths in the horizontal and sagittal planes and velocity profiles in the direction of the cartesian x, y and z co-ordinates. Horizontal movement paths were smoothly curved, segmented or almost linear. Sagittal movement paths were sigmoid. The net velocity profile was usually bell-shaped with longer deceleration than acceleration, but for some slow movements the velocity profile had a plateau. When the net velocity profile was bell-shaped, the averaged sagittal movement paths and normalized x (protraction) and z (lifting) velocity profiles were virtually superimposable for fast and slow movements: thus, movement speed was changed by parallel scaling of protraction and lifting. Comparison of movement paths and velocity profiles amongst the different cats revealed considerable differences. The ż profile was unimodal in one cat and double peaked in five cats: the second component was pronounced in two cats and small in the other three. The ż profile was unimodal and, except for one cat, it had later onset and summit than the first component of the x profile. In contrast to the interindividual differences, there was a high degree of intraindividual constancy over 6–12 months. It is postulated that the interindividual variability depends on chance differences established early during learning of the task and that the imprinted pattern remains, resulting in intra-individual constancy.

Notes: Abstract To assess speed- and gait-related changes in semitendinosus (ST) activity, EMG was recorded from three cats during treadmill locomotion. Selected step cycles were filmed, and hip and knee joint kinematics were synchronized with EMG records. Swing-phase kinetics for trot and gallop steps at 2.25 m/s were compared for gait-related differences. Also, swing kinetics for different gallop forms were compared. With few exceptions, ST-EMG was characterized by two bursts for each step cycle; the first preceded paw off (STpo), and the second preceded paw contact (STpc). The two-burst pattern for the walk was defined by a high-amplitude STpo burst and a brief, low-amplitude STpc burst; at the slowest walk speeds, the STpc burst was occasionally absent. For the trot, the STpo burst was biphasic, with a brief pause just after paw off. With increasing walk-trot speeds, the duration of both bursts (STpo, STpc) remained relatively constant, but recruitment increased. Also, the onset latency of the STpo burst shifted, and a greater proportion of the burst was coincident with knee flexion during early swing. At the trot-gallop transition, there was an abrupt change in the two-burst pattern, and galloping was characterized by a high-amplitude STpc burst and a brief, low-amplitude STpo burst. At the fastest gallop speeds, the STpo burst was often absent, and the reduction in or elimination of the burst was associated with a unique pattern of swing phase kinetics at the knee. Knee flexion during the gallop swing was sustained by two inertial torques related to hip linear acceleration (HLA) and leg angular acceleration (LAA); correspondingly, muscle contraction was unnecessary. Conversely, knee flexion at the onset of the trot swing relied on a flexor muscle torque at the knee acting with an inertial flexor torque (LAA). Rotatory and transverse gallops at 4.0 m/s had similar swing phase kinetics and ST-EMG. Gait-related changes in ST-EMG, particularly at the trot-gallop transition, are not congruent with neural models assuming that details of the ST motor pattern are produced by a spinal CPG. We suggest that motor patterns programed by the spinal CPG are modulated by input from supraspinal centers and/or motion-related feedback from the hindlimbs to provide appropriate gait-specific activation of the ST.

Notes: Abstract In kittens, callosally projecting neurons were labeled by retrograde transport of FITC- (fluorescein isothiocyanate)- and TRITC- (tetramethylrhodamine isothiocyanate)-conjugated latex microspheres injected in two different visual areas (17, 17/18, 19, or postero-medial lateral suprasylvian; PMLS) at postnatal day 3. At postnatal day 57 more than 1200 labeled neurons in visual cortical areas were intracellularly injected with 3% lucifer yellow (LY) in perfusion-fixed slices of the contralateral hemisphere. The distribution of labeled neurons was charted, and LY-filled neurons were classified on the basis of their area and layer of location, and dendritic pattern. The dendritic arbors of 120 neurons were computer reconstructed. For the basal dendrites of supragranular pyramidal neurons a statistical analysis of number of nodes, internodal and terminal segment lengths, and total dendritic length was run relative to the area of location and axonal projection. Connections were stronger between homotopic than between heterotopic areas. Overall tangential and laminar distributions depended on the area injected. Qualitative morphological differences were found among callosally projecting neurons, related to the area of location, not to that of projection. In all projections from areas 17 and 18, pyramidal and spinous stellate neurons were found in supragranular layers. In contrast, spinous stellate neurons lacked in projections from area 19, 21a, PMLS and postero-lateral lateral suprasylvian (PLLS). In all areas, the infragranular neurons showed heterogeneous typology, but in PMLS no fusiform cells were found. Quantitative analysis of basal dendrites did not reveal significant differences in total dendritic length, terminal, or intermediate segment length among neurons in area 17 or 18, and this was related to whether they projected to contralateral areas 17–18 or PMLS. All injections produced exuberant labeling in area 17. No differences could be found between neurons in area 17 (with transient axons through the corpus callosum) and neurons near the 17/18 border (which maintain projections to the corpus callosum). In conclusion, morphology of callosally projecting neurons seems to relate more to intrinsic specificities in the cellular composition of each area than to the area of contralateral axonal projection or the fate of callosal axons.

Notes: Abstract The purpose of this study was to test our hypothesis that the serotoninergic system plays a significant role in airway obstruction during sleep, by focusing on patterns of serotoninergic innervation of the medullary motoneurons involved in upper airway control. We used the combined techniques of retrograde labelling of motoneurons with unconjugated cholera toxin B and immunohistochemistry with antiserum against serotonin (5-HT). The retrograde tracers were injected into posterior cricoarytenoid (PCA), cricothyroid (CT), and genioglossal (GG) muscles of the cat. Motoneurons retrogradely labelled from PCA were identified ipsilateral to the injection site in the caudal part of nucleus ambiguus (NA). Serotonin immunoreactive terminals surrounded their somata and proximal dendrites, suggesting a strong influence of serotonin on the PCA-labelled motoneurons. Motoneurons retrogradely labelled from CT were located ipsilaterally in two distinct groups in the rostral NA and in the retrofacial nucleus (RFN). Selective peripheral nerve section revealed that the CT-labelled motoneurons in the NA had axons in the recurrent laryngeal nerve, whereas the other CT-labelled motoneurons in the RFN were innervated through the superior laryngeal nerve. In the RFN, the pattern of 5-HT innervation in relation to the CT-labelled motoneurons was analogous to that observed with the PCA-labelled motoneurons. In the NA, however, 5-HT terminals made few contacts with the CT-labelled motoneurons, although a dense network of 5-HT terminals was present in the surrounding region. In the GG-labelled motoneuron region of the hypoglossal nucleus, 5-HT terminals were apposed to distal dendrites, not to the soma, indicating less effect of serotonin on GG than on PCA activity. The present results demonstrated that the patterns of 5-HT innervation vary according to the type of motoneurons and their projections to the upper airway.

Notes: Abstract Electrical stimulation of the thalamic nucleus pulvinar was found to influence unit activity in the feline caudate nucleus. Twenty-six (18.3%) units were encountered, in this subcortical region of the brain, that responded to activation of the pulvinar input in anesthetized cats and 41 (54%) in awake animals. In the two types of experiments, stimulation of the pulvinar induced mainly an initial excitatory reaction (81% and 78% of responsive cells, respectively). A latency analysis indicated that the majority of responses occurred at a long latency, while 9 (34.6%) cells in anesthetized cats and 5 (12%) in awake animals were excited at a short latency. The short latency is compatible with the involvement of a monosynaptic pathway between the pulvinar and the caudate nucleus. Units that responded to thalamic stimulation were found predominantly in the posterior regions of the caudate nucleus. These results confirm previous neuroanatomical findings of a direct projection from the pulvinar to the feline caudate nucleus. In awake animals, neurons activated by pulvinar stimulation were also tested, using visual stimuli of various orientations. Out of 41 units, 63% were classified as having “visual responses”. Of these, 5 cells were found to respond selectively to a particular orientation of the visual stimulus. Three of these were excited at a short latency by pulvinar stimulation. The possible involvement of a direct pathway from the pulvinar to the caudate nucleus in the processing of visual information is discussed.

Notes: Abstract We examined the orientation tuning curves of 86 cells located in layer V of area 17, before, during, and after focal blockade of a small (300-μm diameter) region of near-retinotopic register in layer V of area 18 of quantitatively established orientation preference. Such focal blockade revealed three distinct populations of area 17 layer V cells-cells with decreased responses to stimuli of some orientations (21%), cells with increased responses to stimuli of some orientations (43%), and cells unaffected by the focal blockade (36%). These effects were clearcut, reproducible, and generally directly related to the known receptive field properties of the cell recorded in area 18 at the center of the zone of blockade. These effects were also analyzed in terms of alterations in orientation bandwidth in the cells in area 17 as a result of the blockade-bandwidth increases (22%) and decreases (24%) were found; however, these changes were essentially unrelated to the measured receptive field properties. Inhibitory and excitatory effects were most pronounced when the regions in areas 17 and 18 were of like ocular dominance and were of similar orientation preference. Inhibitory effects (suggesting a normally excitatory input) were most dependent upon the similarity of receptive fields; excitatory effects (suggesting a normally inhibitory input) were less heavily dependent.

Notes: Abstract The distribution of immunoreactivities to six amino acids, possibly related to synaptic function, was investigated in the motor nucleus of the cat L7 spinal cord (laminae VII and IX) using a postembedding peroxidase-antiperoxidase technique. Consecutive 0.5 μm transverse sections of plastic-embedded tissue were incubated with antisera raised against protein-glutaraldehyde conjugates of γ-aminobutyric acid (GABA), glycine, aspartate, glutamate, homocysteate, and taurine. This method allowed localization of the different immunoreactivities in individual cell profiles. The results showed that all these amino acids, except homocysteate, could be clearly detected in either neuronal or glial elements in the ventral horn. In cell bodies of neurons in lamina VII, immunoreactivity was observed for aspartate, glutamate, GABA, and glycine. Adjacent section analysis revealed that combinations of immunoreactivity for glycine/glutamate/aspartate, GABA/glycine/glutamate/aspartate and glutamate/aspartate, respectively, may occur in one and the same cell. In the motor nuclei (lamina IX), immunoreactivity to amino acids was observed in two types of neuron. Large cells, probably representing α-motoneurons, were harboring immunoreactivity to both glutamate and aspartate, while a few small neurons in this area displayed a colocalization of glycine, glutamate, and aspartate. Dendrites and axons in the motor nuclei cocontained glycine/glutamate/aspartate, GABA/glycine/glutamate/aspartate, and glutamate/aspartate immunoreactivities. In both laminae VII and IX, taurine-like immunoreactivity was absent in neuronal cell bodies, but highly concentrated in perivascular cells and small cells with a morphology resembling that of glial cells. A punctate immunolabeling, in all probability representing labeling of nerve terminals, could be demonstrated in the ventral horn for GABA, glycine, and glutamate, but not with certainty for aspartate or taurine. A quantitative estimate of the covering of cell bodies of α-motoneuron size by immunoreactive puncta revealed that glycine immunoreactive terminal-like structures were most abundant (covering 26–42% of the somatic membrane), while glutamate immunoreactive terminals were seen least frequently (5–9% covering). GABA-immunoreactive terminals covered from 10 to 24% of the soma surface. A colocalization of GABA and glycine immunoreactivities in putative nerve terminals could be shown both in the neuropil and in close relation to cell bodies of motoneurons. These results suggest that among the studied amino acids probably only three, namely GABA, glycine, and glutamate, can be considered to be neurotransmitter candidates in the ventral horn of the cat spinal cord.

Notes: Abstract Cutaneous facial inputs influencing head movement were examined in the conscious and anaesthetised cat. EMG recordings were made in neck muscles of conscious, unrestrained cats in which an unexpected light cutaneous stimulus was applied to the glabrous skin of the planum nasale (PN). These observations established that head aversion movements were associated with synchronised activation of both deep and superficial dorsal neck muscles. In anaesthetised cats in which activity in the motoneurons of the large dorsal neck muscles was examined, mechanical stimulation of the PN or electrical stimulation of the infraorbital nerve (ION) produced a short latency, reflex activation. The reflex could be elicited by excitation of low threshold, rapidly conducting fibres in the ION. Intracellular recording from neck motoneurons showed that there is a short latency, probably disynaptic, excitatory pathway from low threshold nerves in the ION to neck motoneurons, but discharge of neck motoneurons occurred several milliseconds later, presumably as a result of activity in a longer multisynaptic pathway.

Notes: Summary The effects of β -phorbol 12, 13-dibutyrate (PDBu) on the discharge properties of slowly conducting knee joint afferents (group III and group IV fibers) were studied to determine the role of protein kinase C in nociception. Extracellular single unit recordings were made from small filaments dissected from the medial articular nerve in cats anesthetized with alphachloralose. PDBu was applied intra-arterially close to the joint in concentrations of 10-6 up to 10-4 M. The afferents were classified as low-threshold and high-threshold units with regard to their sensitivity to passive noxious and innocuous movements of the knee joint. Following PDBu application, an excitation occurred in 28% of the group III and in 40% of the group IV fibers. An enhancement of responses to passive movements of the joint (sensitization) occurred in 37% of group III and 19% of group IV afferents. In summary, 37.5% of the low-threshold and 50% of the high-threshold fibers proved to be sensitive to PDBu. Most of the PDBu-positive units responded also to bradykinin, whereas only a few PDBu-positive units were sensitive to prostaglandin I2 and E2. We conclude from these results that, in a distinct population of slowly conducting joint afferents, protein kinase C is likely to be involved in the process of transduction. Thus, pain and hyperalgesia may be mediated at least partly by intracellular mechanisms that are linked to protein kinase C.

Notes: Abstract The activity of cells in the magnocellular red nucleus (RNm) was recorded extra and intracellularly in the curarized thalamic cat performing fictive locomotion. The locomoter episodes were detected from the rhythmic activity recorded in the motor nerves of the contralateral hindlimb. It was confirmed that, during fictive locomotion, a large proportion of the rubrospinal cells (56% in our sample) exhibit a rhythmic pattern of activity which is synchronized with the efferent spinal motor nerve activity. On the basis of the intracellular recordings it was established that phases of intense synaptic activity with mixed excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) are involved in this rhythmicity. After eliminating the cerebellar input to the RNm, it was observed that the cells still received intense excitatory and inhibitory inputs, resulting in a continuous modulation of their membrane potential, due to the occurrence of EPSPs and IPSPs. During fictive locomotor like activity and after elimination of the cerebellar afferents to the RNm, it was observed that the spontaneous PSPs in RNm cells (in the case of 45% of the cells) were organized in repetitive subthreshold bursts occurring in phase relationships with the activity recorded in the motor nerves. Some extracellularly recorded cells (12%) showed a rhythmic firing pattern. It is generally recognized that, in the thalamic cat preparation, the locomotor pattern observed in efferent nerves originates from the central pattern generator (CPG) of the spinal cord. It therefore seems likely that the rhythmicity observed here in the RNm may originate from the spinal CPG and be transmitted through the spino rubral pathway ascending in the ventral part of the cord. It is concluded that the spino rubral pathway may transmit both somatosensory information and corollary discharges relating to the activity of the spinal CPG for locomotion.

Notes: Abstract Experiments were performed to determine whether the receptors of the glabrous skin of the cat planum nasale (PN) could function in tactile analysis. Trigeminal projection sites of the PN were first identified using transganglionic transport of wheat germ agglutin-in-horseradish peroxidase and horseradish peroxidase. Restricted projection sites were identified in this way among the interstitial neurons of the trigeminal tract, in the dorsal horn of the medulla, in subnucleus interpolaris and to a lesser extent in subnucleus oralis. Electrophysiological recording in the trigeminal spinal nucleus confirmed the major neuroanatomical findings and confirmed the paucity of PN projections to the trigeminal system. Most neurons innervated from the PN have small receptive fields, are rapidly adapting and responsive to PN vibration at amplitudes as low as 10 μm. Neurons could be entrained at frequencies below 80 Hz. This upper limit for entrainment presumably reflects the lack of pacinian corpuscles in the PN. A limited number of slowly adapting neurons were found, but only responded to PN displacements of 400 μm and above. The data suggest that the PN can function in tactile analysis to a limited degree. The significance of these findings is considered with respect to the organization of neural systems controlling head movement.

Notes: Abstract Intrapontine microinjections of serotonin in acutely decerebrated cats resulted in the bilateral augmentation of the postural muscle tone of the hindlimbs. Optimal injection sites were located in the dorsomedial part of the rostral pontine reticular formation corresponding to the nucleus reticularis ponds oralis (NRPo). In this study, attempts were made to elucidate the cellular basis for the serotoninergically induced augmentation of postural muscle tone by recording the electromyographic (EMG) activity of hindlimb extensor muscles, the monosynaptic reflex responses evoked by electrical stimulation of group Ia muscle afferent fibres and the membrane potentials of hindlimb alpha-motoneurons (MNs). Serotonin injections resulted not only in the augmentation of the EMG activity of gastrocnemius soleus muscles, but also in the restoration of EMG suppression, which was induced by previous injection of carbachol into the NRPo. Extensor and flexor monosynaptic reflex responses were facilitated by serotonin injections into the NRPo. Such reflex facilitation was not induced by serotonin injections into the mesencephalic or the medullary reticular formation. Intrapontine serotonin injections resulted in membrane depolarization of extensor and flexor MNs with decreases in input resistance and rheobase. Spontaneous depolarizing synaptic potentials (EPSPs) increased in both frequency and amplitude. Peak voltage of Ia monosynaptic EPSPs also increased. Serotonin injections which followed carbachol injections resulted in membrane depolarization of MNs along with an increase in the frequency of spontaneous EPSPs and a decrease in carbachol-induced inhibitory postsynaptic potentials. Following pontine carbachol injections, antidromic and orthodromic responses in MNs were suppressed. Discharges of MNs evoked by intracellular current injections were also suppressed, but were restored following serotonin injections. These results indicate that postsynaptic excitation, presynaptic facilitation and disinhibition (withdrawal of postsynaptic inhibition) simultaneously act on the hindlimb MNs during serotonin-induced postural augmentation and restoration.

Notes: Abstract A retinotopic map can be described by a magnification function that relates magnification factor to visual field eccentricity. Magnification factor for primary visual cortex (VI) in both the cat and the macaque monkey is directly proportional to retinal ganglion cell density. However, among those extrastriate areas for which a magnification function has been described, this is often not the case. Deviations from the pattern established in V1 are of considerable interest because they may provide insight into an extrastriate area's role in visual processing. The present study explored the magnification function for the lateral suprasylvian area (LS) in the cat. Because of its complex retinotopic organization, magnification was calculated indirectly using the known magnification function for area 19. Small tracer injections were made in area 17, and the extent of anterograde label in LS and in area 19 was measured. Using the ratio of cortical area labeled in LS to that in area 19, and the known magnification factor for area 19 at the corresponding retinotopic location, we were able to calculate magnification factor for LS. We found that the magnification function for LS differed substantially from that for area 19: central visual field was expanded, and peripheral field compressed in LS compared with area 19. Additionally, we found that the lower vertical meridian's representation was compressed relative to that of the horizontal meridian. We also examined receptive field size in areas 17, 19, and LS and found that, for all three areas, receptive field size was inversely proportional to magnification factor.

Notes: Abstract We studied the modulatory actions of microiontophoretically applied acetylcholine (ACH), serotonin (5-HT, 5-hydroxytryptamine) and noradrenaline (NA), and those of the adrenoceptor agonists phenylephrine (PHE, α1), clonidine (CLO, α2) and isoprenaline (ISO, β) on spontaneous and visually induced activities in cat perigeniculate (PGN) and thalamic reticular (NRT) neurons (only spontaneous) during extracellular recordings performed in vivo. ACH and 5-HT were found to affect the ongoing (spontaneous) and visually evoked activity of PGN cells and also the spontaneous activity of NRT cells in an opposite fashion. ACH inhibited tonic firing and often induced burst activity. By contrast, 5-HT exerted an excitatory influence, which caused a long-lasting, very regular, high-frequency activity between about 35 and 120 Hz. Spontaneous as well as 5-HT-induced firing was found to prefer three distinct frequency ranges: 35–42 Hz, 60–67 Hz and 80–120 Hz. Opposite actions of ACH and 5-HT were also evident when applied simultaneously. ACH dampened the high-frequency activity elicited with 5-HT, and 5-HT could replace the burst activity induced with ACH application by a regular tonic activity. The absolute strength of visual responses (in spikes per second) was only slightly enhanced or reduced by ACH and 5-HT, respectively, but due to the strong effects on background activity, ACH clearly elevated the signal-to-noise ratio and 5-HT reduced it. Despite its excitatory action, 5-HT did not facilitate visual responses. Spontaneous changes in ongoing activity were found to affect the visual response amplitude in the same way. Noradrenaline, the α1-agonist PHE and the β-agonist ISO exerted a weak depressant action on high-frequency maintained activity, but during low-frequency single spike activity and/or burst activity a facilitatory effect was evident, which prevented the generation of burst discharges and slightly increased single spike firing. Visually evoked activity was little affected, but signal-to-noise ratio changed with changes in ongoing activity. The α2-agonist CLO clearly attenuated both spontaneous activity and visual responses. We suggest that, in addition to direct effects of ACH and 5-HT on geniculate relay cells, the balance between the opposite actions of ACH and 5-HT on PGN cells determines the mode of operation in the recurrent inhibitory circuit: either a global, tonic inhibition of relay cells during a dominating 5-HT influence or a less tonic but phasic inhibition during increased activity in the cholinergic system.

Notes: Abstract We examined the influence of acetylcholine (ACh) on the visual response properties of lagged cells in the dorsal lateral geniculate nucleus of anaesthetised cats. By means of electrophysiological techniques, the response of single cells was recorded before, during and after ionophoretic application of ACh. ACh evoked a clear enhancement of the visual response. The initial suppression that a visual stimulus evokes in lagged cells was resistant to the effects of ACh. The characteristic anomalous response component of lagged cells was also present during application of ACh. The difference in latency to half-rise and to half-fall of the visual response that is found between lagged and non-lagged cells was maintained during application of ACh. Taken together, the results support previous evidence from experiments with brain stem stimulation that the fundamental visual response characteristics of lagged cells are state independent.

Notes: Abstract In a previous study, we reported on a selective and long-lasting paradoxical sleep (PS) deprivation in cats following repeated administration of the Parkinson syndrome-inducing neurotoxin N-methyl-4-pheny11,2,3,6-tetrahydropyridine (MPTP). While the characteistic motor deficits occurred only from the 2nd to 3rdday of a 5-day long administration of 5 mg/kg per day MPTP i.p., the PS deprivation started immediately after the first injection and lasted altogether for 11–13 days. The motor deficiencies induced by repeated administration of MPTP are mainly due to the selective depletion of dopaminergic neurons in the nigrostriatal system as the histological and biochemical data show. The immediate onset of PS deprivation and the PS recovery, despite the definite cell loss, suggests a mechanism independent of cell destruction. In our present study we investigated the occasional histological and the PS-deprivatory effect of a single low dose of MPTP in cats. A single injection of 2 mg/kg MPTP i.p. resulted in PS deprivation lasting for 2.5–3.5 h. The duration of other sleep stages showed no significant change and PS recovery was without rebound phenomenon, as in the case of repeated administration. Even a higher single dose of MPTP (5 mg/kg) resulted in no visibly detectable nigrostriatal cell loss. We suggest that the changes in monoamine release and/or turnover are involved in the PS deprivatory effect of MPTP.

Notes: Summary We studied in decerebrate, paralyzed cats, the effect of sinusoidal yaw rotation on upper cervical commissural neurons. The activity of some neurons was modulated by this stimulus, and they were classified as receiving input from the horizontal semicircular canal. The responses, which were mainly type II, were well correlated with the velocity of the stimulus. These commissural neurons, some of them propriospinal, transmit horizontal canal signals to the contralateral ventral horn, presumably to motoneurons, as well as to more caudal levels of the spinal cord.

Notes: Summary Visual response properties were examined in the superficial layers of the superior colliculus (SC) of anesthetized, paralyzed cats before and after i.v. administration of d-amphetamine. Receptive fields (RFs) of single SC units were plotted using small spots of light presented to the contralateral eye. Within the first hour following d-amphetamine injections, RF size gradually increased, reaching a maximum 86 min post-injection. On average, the area of the RF increased by 5.6 times and RF expansion was observed in all single units examined in the superficial layers. Over the subsequent 4–8 h following the injection, RF area gradually decreased and returned to control dimensions. Most RFs displayed asymmetrical patterns of expansion, showing relatively more horizontal than vertical growth. As RF expansion developed, responses to stimuli flashed “on” and “off” at various locations both inside and outside the borders of the control RF became progressively more vigorous. In contrast, no significant changes were noted in directionselective responses at any time after d-amphetamine injections. Using an array of light bar stimuli of different lengths, the strength of surround suppression was found to be significantly diminished by d-amphetamine. The reduction in surround suppression was especially clear for bar lengths which exceeded the diameter of the control RF. No RF expansion was observed in the superficial layers of the SC when d-amphetamine was injected intravitreally. Furthermore, d-amphetamine had no discernable effect on the RF sizes of cells in the visual cortex. These results suggest that the RF changes in the SC were not of either retinal or cortical origin. We conclude that the mean retinal area which can potentially influence the activity of RFs in the superficial layers of the SC may be on average over 5 times greater than the RF area determined using conventional methods and criteria. These findings raise the interesting possibility that the relatively small size and sharp borders characteristic of RFs in the superficial layers arise from local inhibitory networks which delimit a broader field of excitatory activity supplied by retinal and cortical afferent terminals. Thus, in order to generate the RF changes observed here, either these local inhibitory circuits are amphetamine sensitive, or more likely, these inhibitory networks are dynamically modulated by an, as yet unidentified, amphetamine-sensitive input affecting visual RFs in the superficial layers.

Notes: Abstract It has been suggested for a number of years that ganglion cells inform the rest of the brain about contrast in the retinal image. The purpose of the work undertaken here was to demonstrate this fact explicitly. Extracellular recordings were made from X- and Y-cell axons of the optic tracts of anesthetized cats. Responses of these cells to gratings that were near optimal in spatial and temporal frequency were measured for a range of contrasts. For each cell, similar measurements were made at a number of light levels, spanning the photopic to high scotopic (inclusive) ranges. A monotonie relationship between response and contrast was found at all light levels studied, and the same relationship was retained to a good approximation across all light levels. A similar result was also found when nonoptimal spatial frequencies were used as stimuli. These results indicate strongly that X and Y cells inform the cat's brain about contrast in the retinal image. It was also observed that the mean discharge rate of X and Y cells did not change with light level, indicating that no information is relayed to the brain by these cells on the mean light level.

Notes: Abstract To study the biomechanics of the calcaneal ten-don's complex insertion onto the calcaneus, we measured torque-time trajectories exerted by the triceps surae and tibialis anterior muscles in eight unanesthetized decerebrate cats using a multi-axis force-moment sensor placed at the ankle joint. The ankle was constrained to an angle of 110° plantarflexion. Muscles were activated using crossed-extension (XER), flexion (FWR), and caudal cutaneous sural nerve (SNR) reflexes. Torque contributions of other muscles activated by these reflexes were eliminated by denervation or tenotomy. In two animals, minia-ture pressure transducers were implanted among tendon fibers from the lateral gastrocnemius (LG) muscle that insert straight into the calcaneus or among tendon fibers from the medial gastrocnemius (MG) that cross over and insert on the lateral aspect of calcaneus. Reflexively evoked torques had the following directions: FWR, dorsiflexion and adduction; SNR, plantarflexion and abduction; and XER, plantarflexion and modest abduction or adduction. The proportion of abduction torque to plantarflexion torque was always greater for SNR than XER; this difference was about 50% of the magnitude of abduction torque generated by tetanic stimulation of the peronei. During SNR, pressures were higher in regions of the calcaneal tendon originating from MG than regions originating from LG. Similarly, pressures within the MG portion of the calcaneal tendon were higher during SNR than during XER, although these two reflexes produced matched ankle plantarflexion forces. Selective tenotomies and electromyographic recordings further demonstrated that MG generated most of the torque in response to SNR, while soleus, LG, and MG all generated torques in response to XER. Previous studies have shown that interneurons processing afferent information from both XER and SNR differentially excite the MG and LG motoneuron pools. Further, our data demonstrate that forces produced by this differential activation are preserved throughout the calcaneal tendon. We conclude that selective activation of the gastrocnemei permits the animal to take advantage of the complex mechanical insertion of MG and LG at calcaneus and, specifically, to generate different torques at the ankle joint in response to different reflex activations.

Notes: Abstract This study investigated the topographical organization of mesodiencephalic areas for monosynaptic activation of vertical eye movement-related oculomotoneurons (OMNs) in anaesthetised cats. Systematic mapping of effective sites for inducing monosynaptic, excitatory field potentials in vertical OMN pools was performed bilaterally using one concentric bipolar stimulating electrode. These OMN pools included superior rectus, inferior oblique, inferior rectus and superior oblique pools of the oculomotor and trochlear nuclei. All the field potentials induced in each OMN pool were negative and had a latency of 0.8–1.2 ms, indicating monosynaptic activation of the OMNs. Effective stimulating sites for inducing the field potentials were distributed at a rostrocaudal level of A 7.0–9.0 and 1.0–4.0 mm lateral from the midline, but especially at A 7.0–8.0 and 2.0–3.0 mm lateral from the midline. Histologically, they were located within and near the medial part of the Forel's field H. Stimulation at a more caudal level of A 5.0–6.0 and 1.0–2.0 mm from the midline was also particularly effective. This area correspond to the interstitial nucleus of Cajal and the nearby reticular formation. For each OMN pool, the above field potentials were induced bilaterally, but predominantly ipsilaterally. These results suggest the existence of a bilateral, but ipsilaterally predominant, monosynaptic excitatory pathway from Forel's field H to each vertical OMN pool.

Notes: Abstract Latencies of normal and adapted feline vestibulo-ocular reflex (VOR) were studied in five cats by applying ± 20°/s horizontal head velocity steps (4000°/s2 acceleration) and measuring the elicited horizontal or vertical reflex eye responses. Normal VOR latency was 13.0 ms ± 1.9 SD. Short-term adaptation was then accomplished by using 2 h of paired horizontal sinusoidal vestibular stimulation and phase-synchronized vertical optokinetic stimulation (cross-axis adaptation). For long-term adaptation, cats wore ×0.25 or ×2.2 magnifying lenses for 4 days. The cats were passively rotated for 2 h/day and allowed to walk freely in the laboratory or their cages for the remainder of the time. The latency of the early (primary) adaptive response was 15.2ms±5.2 SD for crossaxis adaptation and 12.5 ms±3.9 SD for lens adaptation. This short-latency response appeared within 30 min after beginning the adaptation procedure and diminished in magnitude overnight. A late (secondary) adaptive response with latency of 76.8 ms±7.0 SD for cross-axis adaptation and 68.1 ms±8.8 SD for lens adaptation appeared after approximately 2 h of adaptation. It had a more gradual increase in magnitude than the primary response and did not diminish in magnitude overnight. These data suggest that brainstem VOR pathways are a site of learning for adaptive VOR modification, since the primary latency is short and has a similar latency to that of the normal VOR.

Notes: Abstract The spatial distribution of neuronal responses to frequency-modulated (FM) sweeps was mapped with microelectrodes in the primary auditory cortex (AI) of barbiturate-anesthetized cats. Increasing and decreasing FM sweeps (upwardand downward-directed FM sweeps, respectively) covering a range of 0.25–64.0 kHz were presented at three different rates of frequency change over time (i.e., sweep speed). Using multiunit recordings, the high-frequency domain (between 3.2 and 26.3 kHz) of AI was mapped over most of its dorsoventral extent (as determined by the distribution of the excitatory bandwidth, Q10dB) for all six cases studied. The spatial distributions of the preferred sweep speed and the preferred sweep direction were determined for each case. Neuronal responses for frequency sweeps of different speeds appeared to be systematically distributed along the dorsoventral axis of AI. In the dorsal region, cortical cells typically responded best to fast and/or medium FM sweeps, followed more ventrally by cells that responded best to medium — then slow-, then medium-speed FM sweeps. In the more ventral aspect of AI (which in some cases may also have included cells located in the dorsal region of the second auditory field, AII), neurons generally preferred fast FM sweeps. However, a comparison of maps from different animals showed that there was more variability in the distribution of preferred speed responses in the ventral region of the cortex. The directional preference of units for FM sweeps was determined for the sweep speed producing the strongest response. Direction selectivity appeared to be nonrandomly distributed along the dorsoventral axis of AI. In general, units that responded best to upward-directed FM sweeps were located in the more dorsal and ventral aspects of AI while units that responded best to downward-directed FM sweeps were usually located in the mid-region of AI. Direction selectivity was also determined for multiunit responses at each of the three FM sweep speeds. In general, there was a relatively close agreement between the spatial distributions of direction selectivity determined for the strongest response with those calculated for the fast and medium speeds. The spatial distribution of direction selectivity determined for slow FM sweeps deviated somewhat from that determined for the strongest response. Near the dorsoventral center of the mapped areas, the distribution of units that responded best to downward sweeps tended to overlay the distribution of units that responded best to slow speeds, suggesting some spatial covariance of the two parameters. However, when the analysis was extended over the entire region of cortex examined in this study, the point-by-point correlation between preferred speed and direction selectivity was not statistically significant. In addition, when neural responses obtained from the dorsal and ventral subregions were analyzed separately, no significant correlation was observed between these two response parameters. This suggests that, for a given cortical location, the response properties of direction selectivity and preferred speed are derived from distinct neural processing mechanisms. Significant observations were also made between preferred FM sweep speed and excitatory bandwidth (i.e., Q10dB and Q40dB) such that units that responded best to slower FM speeds also seemed to have higher Q10dB and Q40dB (i.e., were narrowly tuned) and vice versa. In addition, units that responded well to a broadband transient stimlus in general preferred faster FM sweeps and vice versa. Although these correlations were significant across the entire dorsoventral extent of AI investigated in this study, they were stronger for responses in the dorsal subregion of AI. For direction selectivity, statistically significant correlations with these response parameters were observed more often in the dorsal than the ventral regions of AI. The apparent spatial segregation of neuronal responses to different FM sweep speeds and sweep directions distributed along the isofrequency domain of AI suggests that the global aspects of cortical function are compatible with psychophysically derived notions of parallel streams of processing for different aspects of FM signals.

Notes: Abstract This study analyzed changes in the performance of a reaching task and its adaptive modification produced by reversible inactivation of three sites within the forelimb representation of the motor cortex (MCx, area 4γ) in five cats by microinjections of muscimol. Two sites were located in the lateral MCx, rostral (RL-MCx) and caudal (CL-MCx) to the end of the cruciate sulcus, where intracortical microstimulation (ICMS) produced contraction of the most distal muscles. The third site was located more medially, in the anterior sigmoid gyrus (RM-MCx) where ICMS primarily produced contraction of more proximal muscles. The task required the animals to reach into a horizontal target well, located in front of them at one of three possible heights, to grasp and retrieve a small piece of food. The height of the reach was primarily achieved by elbow flexion. Grasping consisted primarily of digit flexion, and food retrieval consisted of forearm supination and shoulder extension. In some blocks of trials, an obstacle was placed in the path of the limb to assess the animal's ability to adaptively adjust the kinematic characteristics of their response trajectory. In normal animals, contact with the bar on the first trial triggered a corrective response at short latency that allowed the paw to circumvent the bar. On all subsequent trials, the trajectory was adapted to prevent contact with the obstacle, with a safety margin of about 1 cm. Inactivation at all sites produced a slowing of movement, a protracted and extended forelimb posture, and increased variability of initial limb position. In addition, inactivation of RL-MCx immediately produced systematic reaching errors, consisting of hypermetric movements, as well as impaired grasping and food retrieval. The degree of hypermetria was similar for all target heights and was not associated with alterations in trajectory control. During inactivation, animals did not compensate for the hypermetria by reducing paw path elevation, suggesting a defect in kinematic planning or in adaptive control. This was confirmed by finding that trajectory adaptation to avoid bar contact was impaired during RL-MCx inactivation. The short latency corrective response, triggered by contact of the limb with the obstacle was, however, preserved. Inactivation of CL-MCx did not impair aiming, grasping, or adaptation immediately after injection. However, impairments occurred after about 1 h postinjection, and at that time mimicked the effects of RL-MCx inactivation. This delay suggests that the drug was acting indirectly on the RL-MCx. Inactivation of RM-MCx did not impair the control of distal muscles, but the reaches became hypometric. The hypometria was greater for higher targets, suggesting that it resulted from weakness. Our results suggest that both rostral regions of the forelimb area of MCx play a more important role in the planning and execution of the prehension response than the caudal portion. We hypothesize that (1) the slowing of movement, forelimb postural changes, hypometria, and grasping and food retrieval impairments are due to defective control of muscles represented locally at each site in MCx and that (2) aiming and adaptation defects, which are produced only by RL-MCx inactivation, result from disruption of integrative mechanisms underlying sensorimotor transformations that normally assure movement accuracy.

Notes: Abstract This study explored the locations and input output properties of a large population of putative premotor neurones of skin reflex pathways in the cat. These neurones, interneurones excited by forelimb skin afferents and antidromically from the T1 motor nucleus (MN) and/or the lateral funiculus (LF, C8/T1 border), termed antidromic cells, were extracellularly recorded at C6-8. Selection of this site was based on data showing that cells retrogradely HRP labelled from the T1 MN were most numerous in C6-8 and the observation that transection of LF at the C8/T1 border abolished most skinevoked postsynaptic potentials of T1 motoneurones. Antidromic cells were located in laminae IV–V, VI and VII. The latencies of antidromic excitation ranged from 0.4 to 1.8 ms, with a tendency for laminae IV–V cells to show longer latencies than laminae VI and VII cells. Latency of skinevoked excitation ranged from 0.6 ms (IV–V cells), 0.8 ms (VI) and 1.4 ms (VII) to greater than 5 ms. The sum of the ortho and antidromic latencies (estimated central latency) of individual cells explained the central latencies of skinevoked postsynaptic potentials in T1 motoneurones. Skin-evoked firing responses (average of eight to ten cells) were earliest and largest in laminae IV–V antidromic cells, and latest and smallest in lamina VII cells. The antidromic cells also received inputs from muscle afferents and descending tracts. The following three results support the suggestion that the sampled antidromic cells are mostly premotor neurones. (1) Projection to the T1 MN via LF was verified in six laminae IV–VII antidromic cells, as tested with threshold mapping for antidromic excitation. (2) Three skinexcited axons of the middle LF projected to T1 MN, as revealed by intra-axonal staining (HRP). (3) PHA-L injection in laminae I–V of C8 anterogradely labelled terminals in lamina IX and LF axons at T1. It is suggested that last order neurones of skin reflex pathways to T1 motoneurones are widely distributed in laminae IV–VII of C6-8 and consist of a variety of neurones with different locations and input patterns.

Notes: Summary We examined whether transient projections in the developing central nervous system of Mammalia form functional synapses on their target neurons, using transient ipsilateral interpositorubral (iIR) projection in kittens as a model system. Intracellular recordings were made from red nucleus (RN) neurons in 26 kittens aged 6–26 postnatal days (PD6-26). RN neurons were identified by monosynaptic excitatory postsynaptic potentials (EPSPs) evoked by stimulation of contralateral nucleus interpositus (IN), and additionally by intracellular staining in a few cells. Sixty-nine out of 362 RN neurons responded to stimulation of the ipsilateral IN. Of the 69 cells, 25 showed depolarizing responses with relatively short latency (2.1–6.7 ms) in kittens up to PD20. Such responses were not observed in older animals. Varying stimulus strength revealed that the potentials were unitary. Paired-pulse facilitation of the potential was observed, suggesting that the depolarizations are EPSPs. Several lines of evidence were obtained suggesting that the EPSPs are evoked monosynaptically. They followed high-frequency stimulation up to 50 Hz, and their latencies remained constant with varying stimulus strength. The latencies of ipsilaterally induced EPSPs were always longer than those of contralateral ones, evidence consistent with the longer course of ipsilaterally projecting axons than that of contralateral ones (Song and Murakami 1990). The age of disappearance of the monosynaptic EPSPs, i.e., PD20, also corresponds roughly with that of the anatomically demonstrable iIR fibers (PD15–PD25; Song and Murakami 1990). It is thus concluded that the transient iIR fibers in kittens form functional synapses on RN neurons.

Notes: Summary Short-latency excitatory postsynaptic potentials (EPSPs) evoked by stimulation in the medial longitudinal fasciculus (MLF) were recorded intracellularly from motoneurons in the cat lumbosacral spinal cord. Monosynaptic and disynaptic EPSPs occurred in most flexor and extensor motoneurons studied. These EPSPs resulted from the activation of fast (〉 100 m/s) descending axons from the MLF to the spinal cord. Several features distinguished monosynaptic and disynaptic MLF EPSPs. Disynaptic EPSPs exhibited temporal facilitation during short trains of stimulation, whereas monosynaptic EPSPs did not. Disynaptic EPSPs, but not monosynaptic EPSPs, were also facilitated by stimulation of the pyramidal tract and the mesencephalic locomotor region. However, disynaptic MLF EPSPs exhibited little or no facilitation when conditioned by short-latency cutaneous pathways. During fictive locomotion, the amplitude of disynaptic MLF EPSPs was modulated, with maximal amplitudes during the step cycle phase when the recorded motoneuron was active, resulting in reciprocal patterns of modulation of flexors and extensors. No comparable change was seen in the amplitude of monosynaptic MLF EPSPs during fictive stepping. These data suggest that the central pattern generator for locomotion modulates disynaptic MLF excitation at a premotoneuronal level in a phase-dependent manner. The effects of lesions made in the MLF and thoracic cord suggest that the interneurons in the disynaptic pathway from the MLF to motoneurons reside in the lumbosacral cord.

Notes: Abstract We are studying the response to injury within the brainstem trigeminal nucleus following trigeminal nerve lesions. We have previously shown with light microscopy and reduced silver stains that unilateral retrogasserian rhizotomy results not only in massive degeneration throughout the ipsilateral spinal trigeminal nucleus; in addition, degeneration is seen in a ventral position at the periobex region (involving caudal pars interpolaris and rostral pars caudalis) in the contralateral spinal trigeminal nucleus. In the present study, we have used electron microscopy to identify the source of the degenerating elements seen bilaterally after unilateral retrogasserian rhizotomy in eight adult felines with survival times ranging from 3 to 20 days. At short survival times (3–7 days) degenerating terminals with round synaptic vesicles (R terminals) and type 1, asymmetric contacts predominate bilaterally, while fewer degenerating terminals with flattened synaptic vesicles (F terminals) and type 2, symmetric contacts are seen. At longer survival times more F terminal degeneration is seen, especially on the contralateral side. Postsynaptic sites and dendrites show minimal alterations. These findings suggest that the degenerating R terminals seen on the contralateral side originate from primary afferents while the degenerating F terminals seen on the contralateral side originate from intrinsic sources involving a crossed internuclear pathway. In addition, the finding of degenerating F terminals may represent a novel form of selective transynaptic change of intrinsic neurons, associated with minimal dendritic or somatic alterations.

Notes: Abstract The contribution of the lateral suprasylvian cortex to pattern recognition was studied by behavioural detection experiments in combination with bilateral lesions of different parts of the lateral suprasylvian areas (LSA) and area 7 in seven cats. In a two-alternatives forced choice task the cats had to discriminate simple outline patterns which were additively superimposed on a structured visual background made up of broadband Gaussian noise. For various stimulus conditions (moving or stationary patterns and/or background) the detection probability (P D) of the cats was measured as a function of the signal to noise ratio (S/N). Each cat was tested before and after the lesion. Four different types of lesion could be distinguished depending on their extent: (1) lesion of parts of the (LSA); (2) lesion of parts of the LSA with undercutting of areas 17, 18 and 19; (3) lesion of area 7; (4) lesion of area 7 and parts of the LSA. 1. We found that a large bilateral lesion of the LSA led to significant deficits in all test situations which were dependent on the existence of relative velocity of moving patterns against a structured background. The ability of the cats to discriminate simple outline patterns which were kept stationary was not reduced. On the contrary, when they were tested with stationary and moving patterns on unfocused (empty) backgrounds, we found, to our great surprise, that the performance of the lesioned cats was significantly improved compared with intact animals. As these lesioned cats had no deficits with moving patterns on a uniformly grey background, we conclude that the deficits with the moving patterns must have been caused by interactions between patterns and background, and not by movement of a pattern per se. 2. As soon as the lesion of the LSA was extended by a bilateral undercutting of areas 17, 18 and 19 we found very severe deficits in all test situations, regardless of whether the patterns were moving or kept stationary, or whether they were superimposed on a background or not. The most substantial deficits occurred when the patterns were moving on a stationary background. In these situations the cats were no longer able to reach the 84% correct criterion. Again, the cats were able to reach criterion with moving patterns on a uniformly grey background indicating that this deficit is probably caused by the interaction of patterns and background and not by motion of the patterns per se. 3. A large lesion of area 7 led to modest but significant deficits of more or less the same degree in all test situations with the exception of quickly moving patterns on a structured background. In contrast, a much smaller lesion of area 7 yielded significant deficits only when the background was moved and there was a low relative velocity between the patterns and the background. 4. In brief, the combination of a lesion of area 7 with that of the LSA roughly provoked a combination of the effects of the two lesions (1 and 3) alone. We found significant deficits in all test situations. We did not find evidence for any type of functional recovery in any of the lesions described. All deficits were permanent. Our results support the idea of a functional segregation between the LSA and area 7. They confirm that the LSA are involved in pattern recognition whenever it is associated with motion in combination with object-background interactions. This suggests an involvement of the LSA in the analysis of object- and self-induced motion. An interpretation of the results of lesioning area 7 is based on the conjecture that the mechanism of vergence movements or of binocular fusion of both retina images might be impaired. Under this condition it seems conceivable to expect double images or a reduced visual acuity because the images are out of focus. This would have a similar effect on the detection performance in each stimulus configuration. In addition, the results of lesion 4 provide evidence that both functional subunits (LSA and area 7) are not able to compensate for one another. Finally, we conclude from the results after lesion 2 that the LSA is part of a system which is based on the cooperation with striate cortex and requires intact primary cortex for its full function.

Notes: Abstract The distribution of optic chiasm input to different types of neurons in pericruciate cortex of cats agreed with previous work using light flashes. Neuron response times served to differentiate the input pathways to pericruciate cortex, and the types of neurons they influence. Input from the optic chiasm arrived in three distinct surges: the first via the superior colliculus, the second via an unidentified pathway, and the third via the visual cortex. A fourth, diffuse surge arrived in the postcruciate cortex via some unidentified pathway. Stimulation of the contralateral side of the optic chiasm had a weaker effect than stimulation of the ipsilateral side; it evoked activity at a higher threshold, with fewer spikes per response, and at a longer latency. The difference in response latency between the two sides was largest on neurons responding to the first surge, decreasing in later surges, and being least on those neurons responding to the last surge. About 2.3% of the postcruciate and 15% of the precruciate neurons responded only to optic chiasm stimulation; they were isolated in the granular layers, and their responses could not be influenced by prior cutaneous input. It is suggested that much of the visual input to pericruciate cortex serves to modulate on-going cortical output and, thereby, the behavior of the animal.