Library

Notes: Zusammenfassung Die Fähigkeit des Hörorgans zur zeitlichen Auflösung kurzzeitiger Signalveränderungen bei monauraler oder binauraler akustischer Stimulation ist nicht nur im Hinblick auf Sprachverarbeitungsprozesse von wesentlicher Bedeutung, sondern betrifft auch die Lokalisation und Selektion im akustischen Umgebungsraum. In diesem Zusammenhang werden elektrophysiologische Untersuchungsergebnisse zur Evozierung spezifischer Reizantwortmuster aus dem primären akustischen Rinderprojektionsfeld AI der Katze bei kurzzeitiger interauraler Laufzeitveränderung vorgestellt. Die verschiedenen Neuronenpopulationen, die durch unterschiedliche Plazierung zweier Ableitelektroden erfaßt werden, deuten auf signifikante Unterschiede im Hinblick auf das Zeitauflösungsvermögen hin. Während für Klickstimulation beide Elektrodenkonfigurationen deutliche Potentialmuster aufweisen, wird für eine kurzzeitige Veränderung der interauralen Laufzeit nur für eine Elektrodenanordnung ein ausgeprägtes Reizantwortmuster evoziert. Dieses ist durch eine abnehmende Erregungsamplitude bei Verkleinerung der interauralen Laufzeitdifferenz und des untersuchten Zeitintervalls gekennzeichnet.

Notes: Summary Neurons responding to deep or cutaneous stimuli are situated in different parts of the ventrobasal complex. Within the cutaneous region elongated clusters of cells with common place and modality properties project to single columns in the somatic sensory cortex. The present study sought to determine to what extent single lemniscal axons contribute terminals to different regions and to different cell clusters. Lemniscal axons, anterogradely labelled by horseradish peroxidase injected into the medial lemniscus of cats were examined light and electron microscopically. Labelled axons bore one or two, mainly anteroposteriorly oriented, terminal ramifications. These ramifications were relatively small when compared to the length of the complex. Some of the axons bore one or two collaterals that ascended towards the dorsal edge of the complex and formed an additional small ramification there. Electron microscopic analyses of labelled lemniscal axons provided further evidence to that already available that most of their boutons synapse on proximal dendrites of relay neurons and on presynaptic dendrites, presumably belonging to interneurons. A concurrent study of Golgi-impregnated ventrobasal neurons showed three morphological types all with dendritic fields of similar extent. From measurements of the lemniscal terminal ramifications and the counting of counterstained cells it was calculated that 50–120 neurons may receive input from a single terminal ramification. However, because of the restricted extent of the ramifications, the elongated clusters of cells projecting to a single cortical column probably receive input from multiple lemniscal axons and not all members of the cluster receive inputs from the same axons.

Notes: Summary In alert cat and monkey, a unit type recorded in the region of the thalamic internal medullary lamina seems to provide the extraretinal signal postulated by Singer (1982) to explain the development of mature receptive field properties in cortical visual neurons. These thalamic units are silent (or silenced) during saccades in all directions; they discharge as soon as the eyes assume a new position. The abolition of this discharge by thalamic lesion, or conversely, its elicitation by electrical stimulation could respectively prevent or facilitate plastic changes in visual cortical areas of kittens.

Notes: Summary The retrograde fluorescent technique was used to label cortical neurons which project to both the caudate nucleus and also to the centromedian-parafascicular (CM-Pf) thalamic nuclear complex. After experimentation with many other pairs of fluorescent tracers, Evans Blue (EB) and Fast Blue (FB) were chosen as the best combination for studying the systems involved. Following injections of EB into the caudate nucleus and FB into the CM-Pf complex, doubly labeled medium-sized pyramidal neurons were present within layer V and VI of specific cortical regions. These cells were found on the inferior bank of the cruciate sulcus, in the anterior limbic area, in the cingulate and anterior sylvian gyri and within the buried cortex of the presylvian sulcus. The doubly labeled cells were relatively few in number compared to the more numerous singly labeled FB (corticothalamic) cells found in layers V and VI, and the very numerous singly labeled EB (corticostriatal) neurons, located in layers II, III, V, and VI.

Notes: Summary The relationship between orientation selectivity and spatial receptive field organization was analyzed. Receptive field maps were made with a dual stimulus technique where an optimally oriented activation slit was presented in the most responsive region to produce activity against which the effect of a test spot in various positions was determined. Both simple and complex cells had receptive fields which were subdivided into adjacent elongated and antagonistic subrogions. When the two stimuli were presented in phase (both ON or OFF simultaneously) the fields had a central enhancement region with a strong suppression flank on one or both sides. Optimal slit orientation was related to the location of the suppression flank relative to the location of the central enhancement region, and the degree of orientation selectivity to the shape of the subregions and the distance between them. Estimated orientation tuning curves calculated from the receptive field maps gave satisfactory first approximations to experimental curves. The relative contribution of enhancement and suppression to orientation selectivity was studied by presenting a test slit in different orientations in phase with an optimally oriented activation slit. The orientation selectivity was produced almost exclusively by the flank suppression indicating that orientation selectivity is produced by inhibitory input. The flank suppression lacked any specific orientation selectivity, and it occurred only when both the central region and the flanks were activated in phase. Orientation selectivity in both simple and complex cells is explained by a receptive field organization where the cells have input from partially overlapping excitatory and inhibitory fields which have their centers slightly displaced from each other.

Notes: Summary A quantitative analysis was carried out on the thalamic ventrobasal (VB) complex of the cat. The following numerical and metrical parameters of the neuronal elements (cells and fibers) were determined: 1. Volume of nucleus: 27.38 mm3 2. Total number of neurons: 243,000 3. Total number of fibers of medial lemniscus: 26,000 4. Volume of arborization space of one lemniscal fiber: 2.26×106 μm3. Numerical data of relay neurons and lemniscal fibers and their relations as basic factors in the estimation of the degree of divergence and convergence of lemniscal input were calculated and compared. It was found that the probable degree of convergence is four-fold (1–4) and of divergence 27-fold (1–27) with regard to the relationship of fibers and cells in the VB. The quantitative data obtained in the VB and our considerations on convergence and divergence were compared with analogous values obtained for the lateral geniculate body LGB. The differences between the two sensory relay nuclei reflect differences in their modes of impulse transmission.

Notes: Summary The microvascular architecture of cat uteri from the 22nd to the 62nd day of pregnancy was investigated on corrosion casts by means of scanning electron microscopy. These findings, concerning the endometrial labyrinthine zone, were compared with those on corresponding semithin histological sections. Each area in the zonary girdle of feline placenta is supplied by a centrally located stem-artery. Such a stem-artery displays branching vessels, which partly anastomose with other areas, and originates from the superficial arterial network of the uterus. It straightly crosses the myometrial and labyrinthine layers and branches several times, forming a funnel-shaped system on the fetal side of the labyrinth. Arterioles ramifying from this system enter the septal capillary network of the labyrinthine zone which is composed of single lamellae with progressively complex shapes during pregnancy. This network is oriented in feto-maternal direction. Venules, originating at the end of an area, converge from the lamellae to stem-veins. These veins link the labyrinth and deep endometrial layers with a venous plexus in the myometrium, which, finally, joins the superficial network of uterine veins.

Notes: Summary Distribution of serotonin nerve fibers in the hypothalamus of the cat was studied using the peroxidase antiperoxidase (PAP) immunohistochemical method. There was a heavy concentration of serotonin nerve fibers in the nucleus suprachiasmaticus, the nucleus ventromedialis and the nucleus dorsomedialis. The distribution pattern of the serotonergic fibers in the cat was principally similar to that of the rat and monkey. However, species differences were noted in the mamillary complex, the nucleus hypothalamicus anterior, the nucleus paraventricularis and the nucleus supraopticus.

Notes: Summary Cats with a natural convergent squint were discovered within a colony of normal Mill Hill cats. In two of them single unit recording was undertaken in area 17. The ocular dominance distribution showed a clear disruption of binocularity in both hemispheres. This lack of binocular units was comparable to cats with artificial, surgically-induced strabismus and differed significantly from the ocular dominance distribution of a normal control group. The existence of these natural, non-albino squinters strengthens the use of cats as an animal model for strabismic amblyopia.

Notes: Summary Residual neurons following chronic surgical disconnection from the cortex were studied by light and electron microscopy in the dorsal Lateral Geniculate Nucleus (LGN) of adult cats. One year after operation the volume of the decorticated LGN had shrunken to approximately half that of the control LGN. The number of nerve cells decreased at the same time, to 13–15% of the control, with relatively higher cell loss in A and A1 laminae than in lamina C. The Golgi, Golgi-EM and EM analysis of the residual neurons revealed that they contain two distinct nerve cell types. (1) 55% of all surviving neurons were identified as geniculo-cortical relay cells, while (2) 45% of the persisting nerve cells were interneurons. These data suggest that in the normal LGN of adult cat 7% (or more) of all nerve cells are local interneurons. Finally, those factors which might contribute to the unexpected survival of many relay neurons to the axotomy-caused retrograde degeneration, are considered and discussed.

Notes: Summary EMG responses, vertical and A-P shear forces and kinematics of “automatic postural responses” to unexpected translational perturbations in the headward and tailward directions were studied in cats. Muscles acting on the major joints of the forelimbs and hindlimbs were studied. Movement of the animals in response to perturbation were highly stereotyped and consisted of two phases: (1) motion of the feet during platform movement while the trunk remained relatively stationary followed by (2) active correction of posture by movement of the trunk in the direction of perturbation. Vertical force changes occurred after the perturbation was well underway (latency 65 ms) and were related to the displacement of the center of mass and active correction of trunk position. Shear forces showed both passive (inertial) and active components and suggested that the majority of the torque necessary for po,stural correction was generated by the hindlimb. EMG responses in forelimb and shoulder muscles were most correlated with increase in vertical force, showing a generalized co-contraction in tailward translation (when these limbs were loaded) and little activity when the forelimbs were unloaded. EMG responses in hindlimb showed reciprocal activation of agonists and antagonists during perturbation with strong synergies of thigh and foot flexors in tailward translation and thigh and foot extensors in headward translation. The forelimb EMG patterns were most consistent with the conclusion that the forelimb is used primarily for vertical support during perturbation. It was concluded that hindlimb EMG responses were appropriate for both vertical support and performance of the postural correction. The hindlimb muscle synergies observed during translation are the “mirror image” of those observed in humans by other workers.

Notes: Summary Between 4 and 10 weeks of age 10 normally reared kittens were bilaterally implanted with osmotic minipumps. The visual cortex of one hemisphere was infused with 4 mM 6-hydroxydopamine while the other hemisphere received only a vehicle solution. The pumps delivered the solutions at 1 μl/h for one week concurrent with monocular deprivation. Subsequent electrophysiological recording was performed blind and revealed a marked effect of the 6-OHDA treatment: while most cells in the control hemisphere were primarily activated by stimulation of the non-deprived eye, cells in the 6-OHDA-treated hemisphere were significantly more binocular. High pressure liquid chromatography revealed that the loss of normal ocular dominance plasticity in 6-OHDA-infused hemispheres was always accompanied by at least a 50% decrease in cortical norepinephrine levels and a smaller decrease in dopamine levels. Furthermore, there appeared to be a positive correlation of the degree of ocular dominance shift and the relative amount of norepinephrine present. These results are consistent with the hypothesis that catecholamines, especially norepinephrine, are normally required for ocular dominance plasticity during the critical period in kittens.

Notes: Summary Spatial summation was studied quantitatively through width response curves made with an optimally oriented test slit of variable width, and by comparing the response to combined presentation of several parallel slits with the response to each slit alone. Prior to summation analysis, the cell's discharge field (DF) was mapped by presenting a test slit ON and OFF across the receptive field. Activation profiles, showing the extension of subregions where light stimulation increased (enhancement) or decreased the firing rate (suppression), were made by presenting an optimally oriented activation slit in the most responsive DF-position. Against this activity the effects of a parallel test slit were determined in a series of broadside positions. Width response curves were made over the subregions of the DF and the activation profiles. Spatial summation was found in all cells, but the width of the summation region was smaller than the width of the subregions in the respective profiles. The width of the summation region was related to the degree of activation rather than to specific locations within the receptive field. The effect produced by several slits presented together deviated from the algebraic sum of the effects produced by each slit alone. Linear summation was rarely found. Accumulated response curves obtained by integration of DF or activation profiles were compared with width response curves to test linearity of summation. Linear summation throughout the whole receptive field was never found. A satisfactory fit was found only over a narrow region showing that summation was linear within a small part of the summation region. Linearity ended near response maxima or minima in the response profiles. The results indicate that the receptive field of simple cells consists of overlapping excitatory and inhibitory fields, and that the exact location and width of enhancement and suppression zones are determined by an activity-dependent balance between excitatory and inhibitory inputs.

Notes: Summary 1. The morphology of secondary vertical vestibular neurons was investigated by injection of horseradish peroxidase (HRP) into cells connected to the posterior canal system in rabbits (lateral-eyed animals) and cats (frontal-eyed animals). Vestibular neurons were identified by stimulation with bipolar electrodes implanted into the ampullae of the anterior and posterior (PC) semicircular canals of pigmented rabbits; in the cat, these cells were identified by natural and electrical stimulation. Axons monosynaptically activated by PC stimulation were injected with HRP in the medial longitudinal fasciculus (MLF). These were later reconstructed by light microscopy after the brains had been processed with a DAB-CoCl2 method. 2. In the rabbit the majority of the axons bifurcated after crossing the midline with one branch ascending and the other descending in the MLF. The ascending branches gave rise to collaterals that terminated in both the trochlear nucleus and the inferior rectus subdivision of the oculomotor nucleus. In addition some axons also sent collaterals into the paramedian pontine reticular formation, the periaqueductal grey and the interstitial nucleus of Cajal. The descending branches were followed to the caudal part of the medulla in the MLF and gave rise to collaterals terminating in the vestibular nuclei, the medullary reticular formation, the perihypoglossal nuclei, the abducens nucleus, and the facial nucleus. In another cell type axons crossed the midline without giving off any collaterals and proceeded caudally in the caudal MLF. The synaptic effects of the two types of cells were concluded to be excitatory and inhibitory, respectively. Cell bodies of contralaterally projecting neurons were located in either the medial or ventro-lateral vestibular nuclei. 3. In the cat we observed two neuron classes, with contralaterally projecting axons, whose synaptic effects are presumably excitatory. Their cell somata were located in the medial vestibular nucleus. Termination patterns were similar to both the trochlear and oculomotor nuclei, but neither projected to the abducens nucleus. One class of neurons was almost identical to that found in the rabbit with the main axon bifurcating in the MLF. The second type lacked a descending branch in the MLF. Axon collaterals of the latter type crossed the midline within the oculomotor nucleus after terminating in the inferior rectus subdivision to reach a similar portion of the ipsilateral oculomotor nucleus. Collaterals of these axons also terminated bilaterally in the supraoculomotor region between trochlear and oculomotor nucleus, the interstitial nucleus of Cajal and prerubral loci (including the fields of Forel). In similarity to the rabbit, presumed inhibitory vestibular neurons were found with axons directed caudally in the MLF without brain stem collaterals. 4. Ipsilateral neurons with ascending axons considered to be inhibitory were only studied in the rabbit. Their cell bodies were located in the superior vestibular nucleus, the axon joining the rostral MLF with major termination sites in the superior rectus and in the inferior oblique subdivisions of the oculomotor nucleus. Other terminations were in the paramedian pontine reticular formation and in the medullary reticular formation. 5. These data indicate strong similarities in the morphology of PC linked secondary vestibular neurons in the two species suggesting paramount importance for this wiring pattern in the spatial organization of eye movements. Variations in the termination patern likely reflect different kinematic characteristics of extraocular muscles necessary for the appropriate, but different, type of compensatory eye movements in lateral-versus frontal-eyed animals. We conclude that the termination pattern of secondary vestibular neurons forms a basic part of the neuronal matrix for space-time coordinated eye-movements and other related vestibular functions. This neuronal network provides a morphological basis for a conversion factor for the transformation of vestibular into e.g. extraocular muscle coordinates.

Notes: Summary Extracellular recordings have been made from 118 electrophysiologically identified neurones lying in the posterior lateral suprasylvian area (PLLS and PLMS) of cats anaesthetized with Nembutal. Eighty-one cells were activated synaptically by the electrical stimulation of cortical and subcortical sites known to be the sources of monosynaptic projections to the lateral suprasylvian area; latencies to such activations have been measured. The locations and sizes of the receptive fields of 55 neurones were determined. The direction sensitivity and ocularity of these cells also were examined. The effects of various pharmacological agonists and antagonists have been observed on visual responsiveness and synaptic excitability. The excitatory effects of subcortical (dorsal lateral geniculate nucleus and pulvinar nuclear complex) electrical stimulation on the activity of suprasylvian neurones were reduced substantially by the iontophoretic administration of atropine. Antagonists of the receptors for the excitatory amino acids reduced the effectiveness, on the single cell evoked activity, of stimulation of the ipsilateral 17/18 border region and contralateral homotopic lateral suprasylvian area. Both classes of antagonist reduced the magnitude of neuronal responses to photic stimulation, and these response attenuations were additive when the antagonists were ejected concurrently. All of the pharmacological effects were reversible and reproducible. These data lend support to the proposition that acetylcholine and an excitatory amino acid are mediators of synaptic transmission of cortical visual processes in the lateral suprasylvian area.

Notes: Summary The relations between the cerebral cortex and the red nucleus have been studied in acute, chloralose anaesthetized cats using intracellular recording techniques. Stimulation of the cerebral cortex induces in rubrospinal cells a short latency excitation followed by a long lasting silent period. The evidence is presented that at least a great part of the latter is due to genuine IPSP evoked in these cells. Three populations of rubrospinal neurones have been distinguished according to the cortical origin of their afferents: one group receives projections from the forelimb cortical area. These cells project to the cervical spinal cord and thus should control the forelimb. The second group receives projections from the hindlimb cortical area. These cells project to the lumbar spinal cord and should control the hindlimb. The third group of rubrospinal neurones receives convergent projections from both forelimb and hindlimb cortical areas. If these cells have collateralized axons terminating in both rostral and caudal spinal cord, they could contribute to the coordination of fore- and hindlimb movements. The projections originate in cytoarchitectonic areas 1–5 i.e. in the primary motor and sensory areas and in the rostral portion of the parietal area. No projection has been found from area 6 (premotor) or from area 7 (caudal parietal). The projection upon single rubrospinal cells has been found to originate from large cortical regions with a large overlap between those with excitatory and inhibitory actions. This could indicate the intermingling of cortical cells transmitting both effects.

Notes: Summary Using laminar field potential analysis, we examined responses elicited by both photic and optic nerve stimulations in 30 kittens of 0–65 days of age and in three adult cats. In adult cats, the response in the visual cortex on optic nerve stimulation is a wave complex which consists mainly of surface positive-depth negative (sP-dN) potentials. By contrast, the response in neonates consists of two surface negative — depth positive (sN-dP) waves. In 2 weeks, preceding the sN-dP waves, an sP-dN wave appears. As age increases, the sP-dN wave becomes of higher voltage and the sN-dP waves become of lower voltage. Thus, the configuration of the response resembles that of adult cats in 3–4 weeks. Both photic and optic nerve stimulations elicit responses of the same configuration in the same area. The extent of the responsive area is exactly the same at any age as in adult cats. Using the orthograde HRP method, we examined terminals of the geniculocortical afferent in 23 kittens of 0–43 days of age. The density of labeled terminals in layer I is much higher in kittens before 1 week of age (n = 8) than in kittens after 1 month of age (n = 5), whereas the density of labeled terminals in layer IV is higher in the older kittens than in the younger kittens. These electrophysiological and morphological changes are correlated in reference to the maturation of the neuronal circuit in the visual cortex.

Notes: Summary A series of simultaneous recordings from several striate cortex neurons were made in paralyzed, anesthetized cats. Recordings were obtained with one or two bundles of extra fine wires and originated from one and two cortical orientation columns. Standard PST histograms and, in some cases, response planes were used to analyse the neuronal receptive fields. Functional connectivity between neurons was assessed by cross-correlation of their spike trains. It was found that 61% of neuronal, pairs found within a column shared the same input, either excitatory or inhibitory. Even if neurons in a pair belonged to two different columns separated by 1 mm lateral distance, 40% of pairs still exhibited shared input coordination. This type of coordination could also encompass all combinations of simple and complex fields in the pair. Direct connections between neurons were found almost exclusively within columns: excitatory connections were found in 20% of cases and inhibitory in 8%. Direct connections were often accompanied by the other types of interactions. Only one example of excitatory and one of inhibitory direct connections were found between columns. In both cases preferred orientations were almost identical.

Notes: Summary The relative efficacy of distributed versus massed reverse occlusion therapy in promoting recovery from the anatomical and physiological effects of monocular deprivation was studied in two experiments performed on kittens raised with one eye occluded from eye-opening until 5 weeks of age. The first experiment explored the effects of different periods (ranging from 0.5 to 4 h) of reverse occlusion imposed daily for 20 days. The second, involving a fixed period of reverse occlusion (20 h), examined recovery with respect to the distribution of that period over a varied number of brief daily sessions. Recovery was assessed in terms of changes in cortical ocular dominance and lateral geniculate cell morphology. Although recovery of both cortical ocular dominance and geniculate cell morphology showed the same overall progression with increasing periods of reverse occlusion, changes were apparent in the lateral geniculate nucleus before changes were evident in cortical ocular dominance. A given period of reverse occlusion was found to be far more effective in promoting recovery when distributed over a number of different exposure sessions than when massed together in just one or two sessions. The data suggest that there is a maximal rate of cortical recovery which is achieved with surprisingly brief daily periods of forced visual exposure of the initially deprived eye.

Notes: Summary The subcortical projections to the lateral dorsal nucleus (LD) of the cat thalamus were studied with retrograde transport techniques. Deposits of horseradish peroxidase (HRP) or fluorescent tracers were placed unilaterally in LD of adult cats, using electrophoretic or pressure injection techniques. Following post-injection survival periods of 1, 2 or 3 days, HRP retrogradely labeled cells were identified in sections reacted with benzidine dihydrochloride; fluorescent labeled cells were identified by fluorescent microscopy. Injections in LD result in retrogradely labeled neurons in all nuclei of the pretectal complex, including the nucleus of the optic tract (NTO), the posterior pretectal nucleus (NPP), the anterior pretectal nucleus (NPA), the pretectal olivary nucleus (NOL), and the medial pretectal nucleus (NPM). Small electrophoretic injections of HRP were used to investigate a possible topographic organization of the pretectal projections. Results from a variety of injection sites indicate only a subtle rostral-caudal gradient. That is, small injection sites in rostral LD result in retrograde labeling of neuron somata in the rostral parts of NTO, NPA and NPP, and throughout NPM. Injections in caudal LD result in labeled cells more caudally situated in NTO, NPA, NPP, and throughout NPM. Injections in the pulvinar (Pul) also result in retrogradely labeled cells in the pretectal complex, particularly NTO, NPP, and NOL. Experiments with injections of distinguishable fluorescent tracers in LD and Pul reveal that many more cells project to Pul than to LD. These experiments also reveal that while neurons that project to LD are intermingled with neurons that project to Pul, the two projections originate from separate sub-populations of cells. These results are discussed in regard to phylogenetic comparison of pretectal projections and subcortical pathways of sensory input to the limbic system.

Notes: Summary Afferent input to the central cervical nucleus (CCN) in the C1–4 segments was studied with degeneration methods after sectioning of dorsal roots (DRs) or lesions in the spinal cord or brain stem. Degeneration in the CCN was heavy after sectioning of the DRs C1–4, moderate after sectioning DRs C5–8, and scanty after sectioning DRs T1–4. One to 2 days after sectioning of the C2 dorsal root the resulting degeneration had a granular appearance. At 4 days after the operation coarser argyrophilic fragments appeared, and this type of degeneration dominated at longer postoperative intervals. Degeneration in the ipsilateral CCN was found after lesions of the ventral and lateral funiculi of the thoracic cord. No degeneration was found after lesions of the dorsal funiculus caudal to T4 or after lesions in the ventral and lateral funiculi of the lumbar cord. Degeneration in the ipsilateral CCN was found after lesions in the brain stem in cases with lesions involving the medial and caudal part of the medulla. These afferents may run in the medial longitudinal fascicle (MLF).

Notes: Summary (1) Participation of the motor cortex in initiating muscle contraction in an isometric tracking task was assessed in cats trained to make accurate force adjustments using forelimb muscles, in response to a vibrissal/visual display stimulus. Behavior in the task was characterized by short reaction times. While the task was performed, recordings of single cortical units were made in zones within area 4γ defined by the effects of microstimulation in forelimb muscles and by receptive fields on the forelimb. (2) Two types of receptive fields with different regional distributions were observed. Cells with simple receptive fields (superficial or deep) were seen throughout the area sampled, consisting of the lateral half of the anterior and posterior sigmoid gyri. Cells whose receptive fields had complex features (directional specificity, temporal lability, multiple foci, etc.) were preferentially located in the cortex rostral to the cruciate sulcus. (3) The area of motor cortex rostral to the cruciate sulcus also differed from the area caudal to the cruciate sulcus in the timing of task-related activity. Neurons that were active before response onset (lead cells), and could therefore contribute to response initiation, were preferentially located in the rostral cortex, and, in general, had complex receptive fields. (4) Lead cells were active at a constant latency from the stimulus, rather than being timed to response onset. However, the modulation of their activity was related to both the direction and magnitude of the force response. (5) These results suggest that the pericruciate motor cortex of the cat contains two functional subdivisions: a caudal one concerned with ongoing movement, perhaps under the control of specific sensory inputs from the responding limb, and a rostral one involved in initiating movement. Because behaviorally relevant stimuli can rapidly activate a specialized population of cells in the rostral cortex, this area is able to participate in responses with short reaction times.

Notes: Summary The cells of origin and terminal distribution of the prefrontal corticotectal projection in the cat has been examined using retrograde cell-labeling with horseradish peroxidase (HRP) and anterograde axon-labeling with HRP or 3H-amino acid autoradiography. All prefrontal neurons labeled from unilateral enzyme deposits in the superior colliculus are pyramidal cells scattered through the thickness of layer V. The ipsilateral prefrontotectal neurons are located most densely in the banks and fundus of the presylvian sulcus and, to a lesser extent, in the anterior and frontal polar part of the gyrus proreus. About 10% as many cells are labeled in the contralateral prefrontal cortex in a similar distribution. Injections of HRP restricted to the superficial layers of the colliculus failed to label cells in the prefrontal cortex. Injections of HRP or 3H-proline-leucine in the region of these prefrontotectal neurons results in axonlabeling mainly, but not exclusively, in the ipsilateral superior colliculus where the labeled fibers are distributed in the layers below the stratum opticum. Labeled axons are especially dense in the intermediate gray layer where, caudally, they are arranged in two horizontally arrayed dorsal and ventral sheets interconnected by periodic columns of dense fiberlabeling interposed between columns of lesser fiberlabeling. Thus, the prefrontotectal projection of the cat here reported is consistent with that described earlier for the rat, but differs markedly from the primate in that prefrontal area 8 in monkeys projects also to the superficial tectal layers.

Notes: Summary Ocular movements of naive and adapted cats were recorded by classical electronystagmography techniques during: (1) sinusoidal vestibular stimulation, (2) sinusoidal optokinetic stimulation, (3) sinusoidal additive visual-vestibular stimulation, and (4) sinusoidal conflicting visual-vestibular stimulation. Adaptation of the horizontal vestibulo-ocular reflex (VOR) was produced in adult cats by sustained combined sinusoidal rotation of the cat and its surroundings (fixed-field conditions). This procedure was applied for four hours for four consecutive days. On the fifth day the VOR in darkness, the OKR, the VOR in the light and the visual suppression of the VOR were studied. VOR gain decreased from day to day and some relative frequency-specificity emerged. The gain of the visually inhibited VOR also diminished after training. This change was also frequency-specific. OKN gain, tested by a set of sinusoidal rotations, was found to be virtually unchanged. In the naive cat, VOR modified by the visual stimulus (fixed or moving) could be computed by an algebraic summation of the VOR and OKR eye movement compensations. After training, the gain of the VOR in situations where the VOR was interacting with the OKR remained easily predictable by the algebraic summation of the isolated VOR and OKR compensations.

Notes: Summary For the experiments reported in this study, recordings were obtained from 246 single units in the middle lateral suprasylvian visual area (LS) of 13 cats. 49 of these cells were subjected to detailed quantitative analysis. The receptive field (RF) organization was examined for directionally specific cells by presenting moving single spots on large moving random dot backgrounds. A cell's response to an optimal spot (in terms of size, direction, velocity) moving on a stationary background inside the excitatory RF (ERF) was compared to in-phase (same direction, same velocity) and anti-phase (opposite direction, same velocity) movement of spot and background. In-phase movement resulted in inhibition of the cell's response (3–100%) in 94% of the cells, while anti-phase movement led to reduced inhibition in 52% of the cells or to facilitation (0.5–327%) in 39% of the cells. By changing the direction of background motion with respect to that of the spot, the directional tuning of the in-phase inhibition and anti-phase facilitation effects was determined. We were able to manipulate the size of the background effects by masking out the background for various proportions of the ERF, and maximizing them by restricting background stimulation to the large inhibitory RF (IRF) surrounding the ERF. These results could be best accounted for by a double-opponent-process mechanism with both RF center and RF surround being directionally selective, but with opposite polarity. It is suggested that this type of mechanism could be involved in the processing of object motion.

Notes: Summary By means of retrograde axonal transport of fluorescent substances, e.g., Propidium Iodide, Fast Blue, and Nuclear Yellow, the present study was made to determine whether or not single neurons in the cat inferior colliculus share ascending and descending projections to the following two pairs of structures, i.e. (1) to the medial geniculate body and cochlear nuclei, and (2) to the superior colliculus and pontine nuclei. Our findings indicate that extremely few neurons, if any, in the inferior colliculus harbor such divergent axon collaterals, although most of the different types of projection neurons are located in the same subdivisions of the colliculus.

Notes: Summary (1)Pinna stimulation evoked rhythmic oscillations in the spinal cord of the decerebrate curarized cat (“fictitious” scratch reflex). The role of different spinal segments in generation of these oscillations was studied. For this purpose, destruction of the grey matter of one or of several spinal segments was performed. Besides, different numbers of caudal segments were disconnected from the rest of the cord by cooling the lateral surface of the cord. ENGs of muscle nerves and activity of spinal neurons were recorded. (2) Different parts of the lumbosacral spinal cord, i.e. the L3 and L4 segments disconnected from the caudal part of the cord as well as the isolated L5 segment, are capable of generating rhythmic oscillations with a frequency (3–4 Hz) typical of the scratch reflex. (3) Rhythmic activity of the more caudal segments (L6-S1) usually appears only provided the rostral segments (L3–L5) generate rhythmic oscillations. However, when the dorsal surface of the L6-S1 segments is cooled, pinna stimulation evokes rhythmic activity in these segments earlier than in the L3–L5 segments. (4) The hypothesis is advanced that the L3–L5 segments are the “leading” ones, i.e., they determine the rhythm of activity in the whole spinal hindlimb centre.

Notes: Abstract Inspection of eye saccades made by head-fixed, trained cats revealed the existence of many eye shifts at an approximately constant velocity during the deceleratory phase of the saccade or at the end of it. Slow eye movements occurring at the end of a saccade are usually referred to as “postsaccadic drifts”. It is shown that the duration and mean velocity of these “drifts” are related to the amplitude of the movement. The kinematics of these slow eye movements are nevertheless different from those of saccades. Slow movements at the end of the gaze shift have longer durations than those occurring during the intersaccadic interval between a saccade and a reacceleration of the eye. A closer study of the drifts of three trained cats showed that they play an important corrective role in reducing the residual error at the end of a saccade or during an intersaccadic interval. This functional corrective role was demonstrated by relating the amplitude of the slow movement to the amplitude of the residual error when the slow velocity eye shift began. It is therefore proposed to name these eye shifts “slow correcting movements”.

Notes: Abstract We measured rotation (horizontal, vertical and torsional) and translation (horizontal and vertical) of the paralysed cat's eye in response to 45° steps of orientation presented in a pseudorandom order around the roll and pitch axes (with respect to the horizontal canals). During changes of position of the animal in the roll plane, the eyes rotated towards the lowest part of the orbit (left with left ear down; top when the cat was upside down, etc.) by an average of 0.55°. Changing orientation in the pitch plane evoked vertical rotations of ±1.42° (upwards eye movement during forwards head pitch) and torsional rotations of ±1.3°. All these rotations taken together suggest that the centre of mass is in front of, below and temporal to the centre of rotation. The eyes translated temporally (thus separating by 0.72 mm) during forward pitching and there was a small vertical displacement (0.23 mm) when the animal was upside down. These findings are discussed with respect to a possible role of the extraocular proprioception system.

Notes: Abstract The cat hindlimb muscles have been classified, traditionally, as flexors and extensors, based on their actions in the parasagittal plane and their patterns of recruitment during locomotion and reflex responses. This study provides a detailed examination of the relative magnitudes of the various moment arms of the cat ankle muscles and the interdependent effects of position in the various axes of motion. We used a method based on observing small sliding movements of tendon in response to small angular displacements of the joint. Surprisingly, we found that the ankle joint of the cat permits substantial motion in three axes (eversion/inversion and abduction/ adduction as well as extension/flexion) and many muscles crossing the ankle joint have their largest moment arms about axes other than extension/flexion. These moment arms often depended on the joint position in the axis of the moment arm and, to a lesser degree, on the extension/ flexion angle as well. For some muscles (notably peroneus longus) there was sufficient variability that the predominant action in neutral posture (axis with the largest moment arm) could change from animal to animal, which may be related to heterogeneities of locomotor and reflex recruitment reported in the companion paper.

Notes: Abstract During stereotyped behaviors such as locomotion, patterns of muscle recruitment are usually quite consistent from animal to animal, even in the face of many surgical and pharmacological reductions. However, as studies of musculoskeletal structure, neuromuscular architecture, and sensorimotor circuitry become more detailed, it is important to ask whether there is some level of organization at which individual differences begin to dominate. This study concentrated on the small muscles of the foot and ankle, using standardized methods that consistently record stereotypical electromyographic activity from prime mover muscles and that permit wellcalibrated stimulation of cutaneous nerves to elicit reflexes during treadmill locomotion. Some muscles (particularly the main ankle extensors, triceps surae, and plantaris) had stereotyped activity during both unperturbed locomotion and reflex responses. Others had stereotyped activity during locomotion but variable reflex patterns among animals (tibialis anterior, extensor digitorum longus, flexor hallucis longus, and peroneus brevis). Still others had variable locomotor activity but reflexes that were consistent (flexor digitorum longus) or variable for only peroneal nerve stimulation (peroneus longus), only plantar nerve stimulation (peroneus tertius), or the two (flexor digitorum brevis). Among muscles with interanimal variability, there seemed to be no particular correlation between locomotor and reflexive recruitment in a given animal. This functional heterogeneity is discussed in terms of the development of locomotor and reflex programs and in the context of structural heterogeneity of some of these muscles that is described in the companion paper.

Notes: Summary Single cells were recorded extracellularly in the nucleus of the optic tract (NOT) in monocularly deprived cats. Monocular deprivation had no effect on the direction specificity of these neurons, i.e. all cells in the left nucleus preferred movements from right to left and all units in the right nucleus preferred movements from left to right in the visual field. Neurons driven from the deprived eye failed to respond to stimuli moving at velocities above 10°/s whereas neurons driven from the non-deprived eye responded to velocities up to and above 100°/s as do neurons in normal cats. In 8 out of the 10 cats tested all cells in the two nuclei could be influenced only from the contralateral eye irrespective whether this was the deprived or the non-deprived eye. In the other two cats the influence from the non-deprived eye on cells in the ipsilateral NOT was found to be normal. This influence is mediated probably via cortico-fugal projections. In the 8 abnormal cats a clear deprivation effect could be assigned for the first time to the non-deprived eye consisting in a loss of its connections to the ipsilateral NOT. Electrical stimulation of the visual cortex revealed, however, the existence of a connection between the visual cortex and the NOT. A possible explanation for the specific deficit with visual stimulation in the cortico-pretectal synapse ipsilateral to the non-deprived eye is discussed in relation to developmental mechanisms. The conduction velocity of retinal input to the NOT and the output of the NOT to the inferior olive remained uninfluenced by visual deprivation.

Notes: Summary Non-cerebellar afferents from visual relays to the vestibular nuclei (VN) of the cat have been re-evaluated with the use of the horseradish peroxidase technique. From our data it can be concluded that: (1) A monosynaptic projection from the nucleus reticularis tegmenti pontis to the VN can be excluded. (2) Monosynaptic projections from the superior colliculus and some of the pretectal nuclei (nucleus of the optic tract, olivary pretectal nucleus) to the nucleus prepositus hypoglossi may constitute polysynaptic visual afferents to the VN, which would account for the residual visual sensitivity of the VN neurons after cerebellar or inferior olivary lesions.

Notes: Summary This paper reports on experiments in which the effect of disconnexion of association fibres from Area 17/18 to the posterior suprasylvian cortex (PSSC) was investigated. In the control experiments, all neurons had large receptive fields in the central 5–10 ° of the visual field without detailled retinotopy. In the medial bank of PSSC, receptive fields were located in the contralateral visual field, while receptive fields of neurons in the lateral bank were located ipsilaterally. Neurons in PSSC could be excited by electrical stimulation of the ipsilateral Area 17/18 boundary, of the medial pulvinar (N. lat. post., pars, lat.) and the lateral geniculate body. About 2/3 of all neurons could be excited from all these regions, although with varying latencies. After acute and chronic subpial undercutting of the representation of the central 5–10 ° of the ipsilateral area 17/18, visual response properties including direction sensitivity, receptive field size and ocularity of PSSC-neurons in the medio-posterior bank did not change significantly. After ablation of the whole contralateral visual cortex (including PSSC and a wide region of the contralateral Clare-Bishop area) the input from the ipsilateral eye was considerably diminished, but other response properties did not change significantly. These essentially negative findings are discussed in relation to different findings of other authors, and it is argued that the subpial undercutting of only the central visual field representation may have prevented damage to the ipsilateral suprasylvian cortex and its afferents, which is difficult to avoid if the whole area 17 is ablated by suction. It is proposed, that association fibres may only “unspecifically” excite neurons in related association areas rather than impose onto them specific response features. These latter are derived, also in association areas, essentially from their thalamic afferents and their intracortical interaction.

Notes: Summary Small electrolytic lesions were made in the flocculus of two adult cats by means of a stereotactic approach avoiding any damage to the cerebellar nuclei. After a survival time of 3 days the animals were killed and the brains fixed and prepared according to standard procedures for ultrastructural studies. The brains of two unoperated cats were similarly treated and served as normal controls. In the experimental animals a large number of boutons in the rostral part of the nucleus prepositus hypoglossi (Ph) ipsilateral to the floccular lesion showed degenerative changes. These were characterized by hypertrophy, a prominent aggregation of densely packed parallel tubules or concentric arrays of cisternae and a filamentous hyperplasia. Only very rarely were such abnormal boutons seen in the caudal half of the ipsilateral Ph, or on the contralateral side or in the unoperated animals. The degenerating boutons contain clusters of pleomorphic vesicles and they establish symmetrical synaptic contacts with somata, dendritic shafts and dendritic spines. Some of the degenerating boutons appear to be of the en passant type. These findings thus affirm the existence of a direct flocculo-prepositus projection in the cat. It is suggested that this pathway could be responsible for mediating information about eye position and velocity to Ph neurons.

Notes: Summary The influence of horizontal optokinetic stimulation on posture and postural readjustments, induced by horizontal rotation of a turntable, were studied in the cat. Optokinetic stimulations at constant velocities lead to modifications of posture depending on the velocity of the stimulus. However, habituation as well as interindividual variability of these postural responses make difficult a systematic and quantitative approach to the phenomenon. Optokinetic stimulations at sinusoidal velocities induced reproductible postural responses, whose phase and gain were studied at different velocities and frequencies of stimulation. At low frequencies (from 0.05 Hz to 0.2 Hz) the postural responses tend to lead the position of the Optokinetic stimulus while a lag appears at higher frequencies (up to 1 Hz). In these conditions the gain increases and seems to depend on the performances of the simultaneously elicited oculomotor response. Induced postural readjustments are also modulated by the relative velocity of the visual stimulation with respect to the cat. A given visual input is more effective on an induced postural readjustment than on the posture of a static animal, especially at low frequencies (from 0.05 Hz to 0.3 Hz). These data extend to the cat the strong visual component of the postural control system previously described in other species.

Notes: Summary Cats were trained to discriminate temperature increases or decreases with the paws of one body half in a T-maze. The discriminatory proficiency was found to be inferior compared to cats who may use all four paws. The accomplishments of cats discriminating temperature decreases were superior to those of cats discriminating temperature increases. After transection of one lateral funiculus at the fifth cervical segment all of the cats lost the ability to discriminate temperatures with the contralateral paws. No thermosensory deficiency of the ipsilateral paws was observed. Five out of six cats recovered some ability to discriminate temperature differences with the contralateral paws, but no cat regained its preoperative proficiency within more than one and a half years postoperatively. The findings are taken to indicate the existence of more than one spinal, ascending, thermosensory pathway in the cat.

Notes: Abstract Stimulation of the mesencephalic reticular formation facilitates responses in the visual cortex elicited from the optic radiation. Using intraveneous administration of cholinergic antagonists we investigated in adult cats and two kittens whether this effect is mediated by cholinergic mechanisms. When administered alone the muscarinic antagonists atropine and scopolamine and the nicotinic antagonist mecamylamine failed to block reticular facilitation and sometimes even enhanced the effects of reticular stimulation. However, when administered in combination muscarinic and nicotinic antagonists eliminated or significantly reduced the facilitation. This was even true when the two antagonists were administered with a time lag of several hours. These results support the notion that reticular facilitation of cortical responses is mediated by cholinergic mechanisms and suggest that this effect is mediated either by a receptor with a mixed pharmacological property or by two independent pathways acting via nicotinic and muscarinic receptors. This hypothesis is discussed in the context of recent evidence on cholinergic transmission and earlier data on the pharmacology of reticular arousal.

Notes: Abstract Cholinergic afferents to the neocortex controlled by the mesencephalic reticular formation (MRF) are known to transiently facilitate cortical excitability. In an attempt to identify the pathway mediating this effect in the cat visual cortex we combined retrograde tracing techniques with immunocytochemical methods to visualize the acetylcholine-synthesizing enzyme choline acetyltransferase (ChAT). In addition we examined, in acute electrophysiological experiments, whether local neurotoxin injections into nuclei of the basal forebrain interfered with the reticular facilitation of cortical evoked potentials. Cholinergic projections to area 17 originate from different centers in the homolateral substantia innominata/internal capsule, the septal nuclei, and the nuclei of the diagonal band of Broca. No direct cholinergic projection from the MRF to the visual cortex was observed. Retrogradely labelled cells intermingled with ChAT-positive neurons in the brainstem generally revealed immunopositivity for catecholaminergic markers. Local injections of neurotoxins in the substantia innominata blocked reticular facilitation, whereas local lesions of the septal nuclei and the nuclei of the diagonal band had no effect on MRF-induced facilitation. The blockage of the reticular facilitation of cortical evoked responses after unilateral lesions of the substantia innominata was bilateral, suggesting a cooperative interaction between basal forebrain structures of the two hemispheres. The anatomical and physiological data are discussed with respect to possible mechanisms of transient brainstem influences on cortical excitability.

Notes: Summary The climbing fibre pathway from the tectum to posterior cerebellar cortex was investigated in chloralose anaesthetized cats. With low threshold electrical stimulation within the deeper layers of the superior colliculus, climbing fibre responses were recorded in a centrally located, longitudinal area of lobulus VII, oriented perpendicular to the long axis of the folia. This same area showed climbing fibre evoked activity regardless of the side of tectum stimulated. Hence, it was concluded that the tectoolivocerebellar pathway terminates bilaterally in the most medial parts of the cerebellar cortex, the termination zones being denoted the a1 zones. The results were discussed in relationship to recent anatomical knowledge of the tecto-olivary projection and of the olivocerebellar projection to lobulus VII, and indicate that descending paths from the brain stem to the inferior olive might “respect” its intrinsic compartmentalization.

Notes: Summary Recordings were made of isometric contractions of single motor units of the cat's m. peroneus longus (PerL). The units were activated by stimulation of dissected filaments of ventral roots. In accordance with the general principles introduced by Burke et al. (1973), the 80 isolated PerL units were classified into three or four type-categories according to their contractile speed and endurance. Three currently used varieties of a “fatigue index” were calculated and found to give equivalent results. Units with a high, intermediate and low resistance to fatigue were responsible for about 22.5, 25.4 and 52.1% respectively of the total muscle force. Two alternative methods for fast/slow categorization were compared: (i) classifying all units as slow that failed to show a “sag” in partly fused contractions (“sagcriterion”, Burke et al. 1973) and (ii) classifying all units as slow that had a more prolonged twitch contraction time than that of fatigue-sensitive units (‘FF vs. S-criterion’). The relative contribution of slow units to total muscle force was about 2.8 times as great (14 versus 5%) for a classification by the FF vs. S-criterion than for a subdivision according to sagging behaviour. When compared to equivalent data from previously published studies of feline hindlimb muscles, peroneus longus was found to resemble gastrocnemius medialis in relative motor unit composition. The maximum force of individual PerL units was, however, on average ≤ 50% of that reported for corresponding types of gastrocnemius units.

Notes: Summary The effect of intravenous infusion of dopamine (10 and 25 μg·kg−1·min−1 consecutively) on visceral blood flow distribution was examined in anesthetized cats using the microsphere technique and electromagnetic flowmetry. Arterial blood pressure did not change in response to dopamine infusion, but blood flow through the superior mesenteric artery, and blood flow in the mucosa-submucosa of the gastric antrum and various gut segments increased significantly. During infusion of the high dose the increase was most marked in the mucosa-submucosa of the antrum (+355%) and distal colon (+371%). By contrast, blood flow decreased in the muscularis-serosa of the gut segments investigated, in the spleen, pancreas, and the hepatic arterial bed. The increase in blood flow through the superior mesenteric artery was blocked by the dopamine antagonist bulbocapnine (10 mg/kg i.v.). The results suggest that the receptors mediating the dopamine-induced vasodilation in the gastrointestinal tract are located in the resistance vessels of the mucosa-submucosa.

Notes: Abstract Afferent fibres, in the inferior splanchnic nerves and lumbar white rami, which supply the colon and its mesentery in the cat, were investigated for their responses to distension and contraction of the colon and to local pressure applied to colon and its mesentery. 1) 63% (177 out of 287) of the axons had resting activity (median 0.3 imp/s). These axons were either unmyelinated (conduction velocity below 2 m/s) or thin myelinated (conduction velocity below 18 m/s). Most axons without resting activity (N=95 out of 106 axons) conducted at less than 1.4 m/s, and most were probably sympathetic efferents. 2) 76 out of 80 afferent units with resting activity (95%) and 8 out of 27 units without (30%) were excited by distension of the colon. The thresholds were largely at intraluminal pressures of around 25 mm Hg or higher. 3) Most afferent units (87%) responded with an increased steady state discharge throughout the distension with or without initial dynamic response. The rest of the afferent units responded only with a transient discharged to distension. 4) Most afferent units reacted in a graded manner to variable intraluminal pressures. 5) In only 43% of the distension-sensitive afferent units could mechanoreceptive sites be located on the wall of the colon or in the mesentery. The majority of the afferent units had one mechanoreceptive site only, some had two. 6) Afferent units reacting to colon distension were also excited by contraction of the colon. 7) The excitability spectrum of visceral afferent fibres in the inferior splanchnic nerves, which are activated by colon distension, suggests that these units are involved in visceral nociception from the colon.

Notes: Abstract Postganglionic sympathetic neurones supplying skeletal muscle and skin can be activated from the preganglionic site via cholinergic nicotinic, muscarinic and non-cholinergic synaptic mechanisms. The experiments described in this paper were designed in order to show that postganglionic vasoconstrictor neurones supplying skeletal muscle can be activated by the naturally occurring discharge pattern in preganglionicaxons when the nicotinic transmission is blocked. For this purpose, the activity was recorded simultaneously from postganglionic vasoconstrictor axons supplying skeletal muscle and vasoconstrictor axons supplying hairy skin. The preganglionic neurones were driven reflexly by stimulation of the arterial chemoreceptors. 1) During blockade of nicotinic transmission muscle vasoconstrictor neurones were activated via the CNS during stimulation of arterial chemoreceptors. This activation is either generated by muscarinic action of released acetylcholine or by a noncholinergic synaptic mechanism. 2) Postganglionic cutaneous vasoconstrictor neurones were inhibited during stimulation of arterial chemoreceptors. During blockade of cholinergic nicotinic transmission these neurones were not activated reflexly by stimulation of arterial chemoreceptors although they received inputs via cholinergic muscarinic and noncholinergic synaptic mechanisms. 3) The results illustrate that postganglionic vasoconstrictor neurones supplying skeletal muscle can not only be activated via non-nicotinic synaptic mechanisms through synchronous repetitive electrical stimulation of preganglionic axons but also by the discharge pattern produced in preganglionic neurones during stimulation of arterial chemoreceptors.

Notes: Summary The effects of supramaximal vagus nerve stimulation on heart rate were studied in newborn rabbits, cats and guinea pigs. The analysis of the stimulus-effect curve revealed that the carlier proposed relationship: logI f/I o=H·f (I o is the steady state PP-interval before andI f during stimulation,f is the stimulus frequency, andH the slope of the line) accurately summarizes the relation in rabbits, while with minor deviations it also holds for newborn cats and guinea pigs. Thus, the vagus effect for each nerve and animal is characterized by the slope of the line,H. In rabbits and cats the vagus effect decreased during the first postnatal week to about 1/3 and 1/5 of the initial value at birth. Guinea pigs, however, did not show such a postnatal change of the vagus effect. In comparison with rabbits and cats these animals are born at a relatively late ontogenetic stage. Therefore, we hypothesized that the decrease in vagus effect is related to the stage of development and occurs mainly before birth in this species.

Notes: Summary The posterior hypothalamus of anaesthetized cats was superfused with artificial CSF through a push-pull cannula and the arterial blood pressure was recorded in the femoral artery. The release of endogenous histamine was determined in the hypothalamic superfusate by a radioenzymatic assay. Intravenous injection of sodium nitroprusside elicited a fall of blood pressure which was accompanied by an increase in the rate of release of endogenous histamine in the posterior hypothalamus. Similary, a controlled bleeding lowered the arterial blood pressure and enhanced the release of histamine. The durations of depressor responses to nitroprusside or controlled bleeding coincided with the duration of the changes in the rate of release of histamine. Intravenous injection of chlorisondamine also lowered the arterial blood pressure and augmented the release of histamine. However, the hypotension lasted longer than the increased release of histamine in the hypothalamus. Intravenous injection of noradrenaline elicited a rise in the arterial blood pressure which was associated with an increase in the release of histamine in the posterior hypothalamus. Intravenous injection of tramazoline led to a long-lasting hypertension and to a short-lasting increase in the release of histamine. Transection of the spinal cord at C1/C2 elicited a pressor response which was followed by hypotension. Increase and decrease in the arterial blood pressure were associated with an increased rate of release of endogenous histamine. A second transection of the spinal cord at a higher level did not influence either blood pressure or rate of release of histamine. It is concluded that increases and decreases in the arterial blood pressure enhance the rate of release of endogenous histamine in the posterior hypothalamus of the anaesthetized cat. The alterations in the release of histamine seem to represent an immediate response of the hypothalamus to changes in peripheral blood pressure.

Notes: Summary Substance P-like immunoreactivity (SPLI) was studied by immunocytochemistry and radioimmunoassay in the cerebral arteries, choroid plexus and dura mater of the guinea-pig, rabbit, cat and man. The highest concentrations were found in cerebral blood vessels: 6.1±2.3 pmol/g (guinea-pig), 9.0±1.1 pmol/g (rabbit), 7.1±0.4 pmol/g (cat), and 2.4±0.9 pmol/g (man). Lower levels were obtained in the choroid plexus and dura mater. The distribution of substance P (SP)-immunoreactive nerve fibres found in various regions of the guinea-pig correlated well with the amount of SPLI measured. Sympathectomy did not alter the concentration of SPLI in the dura mater or in cerebral blood vessels. Electrical field stimulation or 124 mM potassium enhanced the spontaneous efflux of SPLI by 10 and 20%, respectively, from superfused pial arteries in vitro. These data are in support of a functional role of perivascular SP within the cranial circulation.

Notes: Summary The cochlear microphonic (CM) was recorded differentially with subcutaneous electrodes at the vertex and a variety of positions on the head and neck of the cat, and the phase and amplitude were compared with simultaneous recordings from vertex and contralateral ear electrodes. Recordings were made in bilaterally hearing animals, both with and without ear canal occlusion, following unilateral labyrinthectomy, and in white-coat cats with hereditary unilateral deafness, and in different age-groups. The cochlear microphonic was in phase with the contralateral recording at all electrode sites except those in the immediate vicinity of the stimulus ear. The amplitude was less at the circumaural positions and greater at cervical locations. The results were consistent in all age-groups and in bilaterally and unilaterally hearing animals. Precise electrode placement in the near-field conditions around the stimulus ear is therefore critical, especially for phase, while far-field conditions would appear to predominate at the remaining electrode sites.

Notes: Molekulare Metall-Cluster gibt es in mittlerweile kaum noch überschaubarer Anzahl und Vielfalt. Sie ermöglichen es, spezifische Zwischenprodukte oberflächenkatalysierter Reaktionen modellhaft zu erzeugen, sie dienen als Edukte für sehr reaktive einkernige Komplexfragmente, und sie können Reaktionscyclen in Gang bringen, bei denen der Cluster intakt bleibt. Der letzte Aspekt wird in diesem Fortschrittsbericht behandelt. Der gegenwärtige Kenntnisstand der Cluster-Katalyse wird kritisch betrachtet, und Möglichkeiten für einzigartig an Mehrmetallatomzentren ablaufende Reaktionen werden erörtert.

Notes: Das Interesse der chemischen Forschung richtet sich zunehmend auf zusammengesetzte, “komplexe” Systeme mit speziellen Eigenschaften und Funktionen. Als Komponenten solcher Systeme finden 1,4-Diazine wachsende Beachtung. Unter 1,4-Diazinen sollen hier Pyrazin und seine Derivate sowie Verbindungen mit Pyrazin-Teilstruktur verstanden werden; Beispiele sind Chinoxalin, Phenazin, Pteridin, Flavin und deren Derivate. Alle diese Verbindungen zeichnen sich durch ein niedrig liegendes unbesetztes π-Molekülorbital und durch die Fähigkeit zur Brücken-Koordination aus. Die Kombination dieser beiden Eigenschaften bedingt eine spezifische Reaktivität der 1,4-Diazine und insbesondere der Stammverbindung Pyrazin. 1,4-Diazine eignen sich ausgezeichnet für Untersuchungen zum inter und intramolekularen Elektron-Transfer bei organischen, anorganischen und biochemischen Reaktionen. Im Redoxsystem der 1,4-Diazine ist die paramagnetische 7π-Elektronen-Zwischenstufe außerordentlich stabil, während die 1,4-Dihydro-1,4-diazine mit 8 π-Elektronen im sechsgliedrigen Ring aufgrund der potentiellen Antiaromatizität und des hohen Elektronenüberschusses nicht generell zugänglich sind. Die inhärente Difunktionalität und das niedrig liegende unbesetzte Molekülorbital des Pyrazins ermöglichen die Bildung von Koordinationspolymeren mit ungewöhnlichen elektrischen und magnetischen Eigenschaften. Die an Pyrazinen beobachteten Phänomene lassen sich schließlich zur Interpretation der Reaktivität natürlich vorkommender 1,4-Diazine heranziehen; diskutiert werden Flavine und biolumineszierende Naturstoffe.

Notes: Die Farbsofortphotographie, die auf der Farbstoffdiffusion basiert, ist seit ihrer Einführung (1963) ein kommerzieller Erfolg. Dies ist sicherlich zum Teil auf den spektakulären Aspekt dieser Erfindung zurückzuführen; aus demselben Grund denkt man dabei aber oft nur an die Apparatur und läßt die Chemie außer acht. Überdies war die Bildqualität zunächst schlechter als bei der konventionellen Farbphotographie. Inzwischen wurden nun photographische Materialien für die Farbsofortphotographie entwickelt, mit denen die Bildqualität sich der Qualität der gewöhnlichen Farbbilder nähert. Es ist wenig bekannt, daß die Chemie und insbesondere die Organische Chemie die Grundlage dieser neuen photographischen Produkte schafft. Erkenntnisse auf diesem Gebiet haben nicht nur die Farbstoff-und die Polymerforschung befruchtet, sondern vor allem die Suche nach besseren Farbstoffdiffusionssystemen angeregt. Das Resultat aller dieser Anstrengungen ist eine genau arbeitende, mikroskopisch kleine chemische Fabrik. Nach wie vor eröffnen sich der photographischen Industrie hierdurch lohnende Aussichten.

Notes: CC-Bindungen werden in vielen Reaktionen durch Addition von Radikalen an Alkene geknüpft. Für gezielte Synthesen ist die Kenntnis des Mechanismus wichtig. Die Geschwindigkeit der Addition von Alkyl-Radikalen an Alkene wird vor allem durch polare und sterische Effekte bestimmt. Die Stabilitäten der Edukte und Produkte sind hingegen von untergeordneter Bedeutung, weil in diesen exothermen Reaktionen sehr frühe Übergangszustände durchlaufen werden. Die Reaktivitäts- und Selektivitätsabstufung läßt sich mit der Grenzorbitaltheorie beschreiben; bei Reaktionen mit nucleophilen Radikalen dominiert die SOMO-LUMO-, bei Reaktionen mit elektrophilen Radikalen die SOMO-HOMO-Wechselwirkung. Ein unsymmetrischer Übergangszustand - das Radikal nähert sich bevorzugt einem der C-Atome des Alkens - erklärt die großen Unterschiede in den sterischen Effekten von α- und β-Substituenten der Alkene. Regio- und Stereoselektivität lassen sich vorhersagen; sie werden im wesentlichen von sterischen Effekten hervorgerufen.