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Notes: Summary The fetal microvascular architecture of the feline near-term placenta was investigated using scanning electron micrographs of partially fractured corrosion casts from plastic-filled vessels. The findings were compared with those on corresponding semithin histological sections. The branches of both umbilical arteries and veins roughly follow a course parallel to the zonary girdle on the allantochorionic side of the feline placenta in an acute-angled pattern of ramifications. They join the double-layered capilary networks in the chorionic lamellae of the labyrinth, which generally exhibit a chorio-uterine orientation and are partially twirled. On the allantochorionic side of the labyrinth, these fetal capillary networks are “suspended” on the maternal stem-artery-system of the placenta; on the uterine side, they have peduncular or tuft-like endings of capillary loops and are flattened by the uterine septa, which at this level converge into the maternal veins. The chorionic capillary lamellae have a variable breadth and length and therefore need shorter or longer arterioles and venules from the allantochorionic side to become irrigated at any level of the labyrinth. As a result, the feline placenta is characterized by a generally one-way crosscurrent type of materno-fetal blood flow.

Notes: Summary The termination of the fibers from the dorsal column nuclei (DCN) to the midbrain has been investigated in the cat with the degeneration method, the anterograde horseradish peroxidase (HRP) method and autoradiography after 3H-leucine injections. The results show that the DCN project to several midbrain regions. The external nucleus of the inferior colliculus (IX) receives the heaviest projection from both the gracile and cuneate nuclei. The DCN fibers form three joint terminal zones in IX. Each terminal zone contains clusters with dense aggregations of DCN fibers. Fairly dense terminal networks are found in the posterior pretectal nucleus (PP) and the compact part of the anterior pretectal nucleus (PAc) as well. More scattered DCN fibers are present in the cuneiform nucleus (CF), the lateral part of the periaqueductal gray (PAG1), the red nucleus (NR), the nucleus of the brachium of the inferior colliculus (B), the mesencephalic reticular formation (MRF) and the intermediate and deep layers of the superior colliculus (SI, SP). The projections to all regions are mainly contralateral. Most of the few ipsilateral fibers terminate in IX. A somatotopic organization was seen in IX and NR. The gracile fibers terminate preferentially in the caudal and lateral part of IX and the cuneate ones preferentially in its rostral and medial part. In the red nucleus the gracile fibers terminate ventral to the cuneate ones. In the pretectal region there was a predominance for gracile fibers. There also appeared to be quantitative differences in the projections from various levels of the gracile nucleus, with more midbrain projecting fibers originating in the rostral than in the middle and caudal parts of the nucleus.

Notes: Summary In a series of comparative anatomical studies on the ceca of various mammals the cat was chosen as representative of a “typical” carnivore. In the domestic cat, the cecum is conspicuously small and macroscopically relatively undifferentiated in comparison to most herbivores. Microscopically (light, scanning and transmission electron microscopy), however, it is characterized by an abundance of goblet cells and enterocytes rich in organelles, suggestive of functional activity. In addition to the morphological description, which also includes arterial supply and mesenteries of the cecum, the discussion is focussed on 1) the possible functional significance of the numerous goblet cells 2) a general categorization of the different types of ileal-caeco-colical junctions and 3) speculations concerning the justification for considering the carnivore cecum as being rudimentary.

Notes: Summary The projections to the midbrain from the spinal cord have been investigated in the cat with the degeneration technique and by using horseradish peroxidase (HRP) as an anterograde tracer. Two types of spinal cord lesions were performed: 1) Cordotomies at cervical or thoracic levels transecting the ventral and lateral funiculi. 2) Transections of the ventral, ventrolateral, dorsolateral or dorsal funiculus, respectively, at cervical levels. In the anterograde tracing experiments HRP was injected into the spinal cord at cervical, lumbar or sacral levels. The results show large projections to the lateral and ventrolateral parts of the periaqueductal gray (PAG1), the posterior pretectal nucleus (PP) and the nucleus of Darkschewitsch (D). More moderate projections go to the medial division of the periaqueductal gray (PAGm), the cuneiform nucleus (CF), the mesencephalic reticular formation (MRF), lateral part of the deep layer of the superio colliculus (SP) and magnocellular medial geniculate nucleus (GMmc), while scattered spinal fibers are present in the dorsal part of the periaqueductal gray (PAGd), the external inferior collicular nucleus (IX), the intermediate layer of the superior colliculus (SI), the lateral part of the red nucleus (NR) and in the Edinger-Westphal portion of the oculomotor nucleus (3). In addition a few fibers are present in the interstitial nucleus of Cajal (CA) and anterior pretectal nucleus (PAc). The results indicate that at midcervical levels most of the spinomesencephalic fibers ascend in the ventral funiculus, with only a moderate fraction ascending in the ventral half of the lateral funiculus. Almost no fibers ascend in the dorso-lateral funiculus and none appear to pass in the dorsal funiculus. No distinct somatotopic pattern was found in the spinomesencephalic projections, but more fibers from cervicobrachial segments terminate in the rostral than in the caudal parts of the terminal fields in PAG, CF, SP and IX, while the lumbar fibers were more numberous in the caudal parts. PP seems to receive spinal fibers mainly from the caudal half of the cord.

Notes: Summary Injections of 3H-leucine were made in the entopeduncular nucleus or dentate nucleus of the cerebellum in eight cats. The terminal projection zones of both pathways in the thalamus were studied using the sagittal plane and their relationships to one another as well as to cytoarchitectural boundaries of thalamic nuclei were compared. The data indicate that the territories controlled by the two projection systems are almost entirely segregated. The segregation is mainly along the antero-posterior axis as the main pallidal projection zone occupies the medio-ventral VA while the main dentate projection zone lies posterior to it in the VL. Furthermore, the dorsolateral part of the VA not occupied by pallidal projections receives dentate projections. In the VM, both afferent systems terminate in the lateral part of the nucleus with pallidal territory located anteriorly and dentate territory located posteriorly, again without overlap. As the delineations of nuclear subdivisions in the ventral thalamus of the cat have been a subject of some controversy, it is suggested that the boundaries of the VA, VL and VM in the cat thalamus be defined on the basis of basal ganglia and cerebellar projection zones.

Notes: Summary The fluorescent retrograde double-labeling technique has been used to determine whether corticospinal neurons in the cat sensorimotor cortex distribute collaterals to the lower brain stem reticular formation. In this study the fluorescent tracers Nuclear Yellow and Diamidino Yellow 2HCl were used in combination with Fast Blue. One tracer was injected unilaterally in the spinal cord and the other was injected ipsilaterally in the bulbar medial reticular formation. The distribution of the retrogradely labeled neurons was studied in the contralateral hemisphere. In the sensorimotor cortex a large population of neurons was found which were labeled from the spinal cord and were double-labeled from the brain stem. These branching neurons were concentrated in the rostromedial part of area 4 and the adjoining lateral part of area 6. In this region the percentages of corticospinal neurons which were double-labeled from the brain stem ranged from 5% laterally to 30% medially. In two cats it was demonstrated by means of the anterograde transport of HRP that the corticobulbar fibers from this region which must include the corticospinal collaterals are distributed to the reticular formation of the lower brain stem. In view of the fact that the double-labeled neurons are concentrated in the anterior part of the motor cortex, those branching neurons are in all likelihood involved in the control of neck, back and shoulder movements. This control is probably exerted by way of two routes i.e. by way of the direct corticospinal connections to spinal interneurons, and by way of the indirect cortico-reticulospinal connections established by the cortical fibers to the bulbar reticular formation. The present findings suggest that this dual control may be exerted by one and the same cell.

Notes: Summary (1) Ipsilateral cortico-cortical and thalamo-cortical projections to the cat motor cortex were determined from the locations of retrogradely labeled neurons following single small intracortical injections of HRP in area 4γ. These projections were also examined by studying the distribution of anterogradely transported axonal label following multiple injections of HRP or of tritiated amino acids in areas 1–2 of SI and in area 2pri (SII). (2) The number of retrogradely labeled cells in areas 1–2 and in area 2pri differed markedly between HRP injection sites located in the precruciate (anterior sigmoid gyrus) and postcruciate (posterior sigmoid gyrus) subregions of area 4γ. These associational projections from primary and secondary somatosensory cortices were dense to postcruciate subrogions but weak to the precruciate subregions. (3) The associational projections from areas 1–2 and from area 2pri to the postcruciate subregion of area 4γ were topographically organized, but no clear topographic organization could be demonstrated for the precruciate projection. (4) Anterograde terminal labeling following injection of either HRP or tritiated amino acids into areas 1–2 and area 2pri confirmed the preferential projection of somatosensory cortex to the postcruciate subregion of motor cortex. The projection from somatosensory areas 1–2 was uniform over its terminal field, but that from area 2pri was more patchy and complex. (5) HRP injections in area 4γ gave rise to lamellae of labeled neurons in the ventrolateral nucleus of thalamus (VL). A topographic relationship was found between the site of injection and the location of the lamella of labeled neurons. (6) The percentage of retrogradely labeled neurons in the shell zone surrounding the border of the ventrolateral nucleus and the ventrobasal complex (VB) was greater following postcruciate than precruciate injections, whereas fewer retrogradely labeled neurons were found in central lateral nucleus (CL) after postcruciate injections than after precruciate injections. (7) These observations support the hypothesis that differential cortical and thalamic projections to different subregions of area 4γ may give rise to the different physiological properties of neurons observed in these subregions (Vicario et al. 1983; Martin et al. 1981).

Notes: Summary Pyramidal command of Skin Potential Response (SPR) was investigated in 20 cats paralyzed by gallamine and under a halothane anaesthetic. For each animal, a transection of the medulla sparing only the pyramidal tract was carried out. The pyramidal tract and Mesencephalic Reticular Formation (MRF) were stimulated before and after the transection. Results taken before transection show that the SPR can be elicited from stimulation of the pyramidal tract and the MRF. After transection, stereotaxic stimulations of the pyramidal tract still evoked the SPR even after aspiration of the medullary tissue posterior to the section and overlying the pyramids. Control reticular stimulations with higher stimulus intensities failed to evoke the SPR. These results show that stimulation of the pyramidal tract can elicit the SPR independently of reticulospinal neurons. It is hypothesized that a group of corticospinal fibers could transmit volleys having autonomic activity on preganglionic autonomic neurons of the intermediate zone of the grey matter.

Notes: Summary Afferents of the cortical pupillo-constrictor areas (PCAs) of the cat were studied using the horseradish peroxidase method. PCAs receive heavy cortical inputs from areas 7, 19, 21, the lateral suprasylvian area, the splenial visual area, and subcortically from the claustrum, the intralaminar nuclei, the pulvinar-lateral posterior nuclear complex.

Notes: Summary 1. In cats trained to track a moving display by making rapid, isometric force adjustments, responses are characterized by extremely short reaction times (60–70 ms) and a stereotyped temporal configuration. The animal uses early derivatives of display movement to scale force responses to target stimuli of different sizes according to a learned relationship between initial display motion and required force (Ghez and Vicario 1978a, 1978b). In the present study we altered that relationship by using double stimulation and delayed feedback to assess the animals' ability to update their responses. 2. In experiments where a second target stimulus followed the first after a controlled interval (15–120 ms) on random trials, the animal modified its response in the appropriate direction with little or no increase in reaction time. When the second stimulus called for a return to baseline, the animal aborted the ongoing response. When the second stimulus called for a doubling of force, the animal increased its phasic force output; however, this increase was not sufficient to reach the new target level and late responses were emitted. 3. The control response which followed each experimental double stimulation trial showed consistent differences from other controls in the amplitude of both peak force and peak dF/dt. Control responses following trials calling for a return were reduced in size; those following stimuli requiring response doubling were increased. We concluded that the experimental trials not only elicited modification of ongoing responses but also caused the animal to alter its internalized gain function relating initial display derivatives to required force. 4. In experiments where feedback was delayed after giving a first target stimulus such that the compensatory display failed to reflect the animal's initial response, the animal emitted a new updated response 70–80 ms after the first. The display trajectory which caused the cat to update its response on delayed feedback trial was identical to that of control trials with long reaction times. In this case, however, the information eliciting response updating had to be derived as a difference between the actual display trajectory and that expected by the animal, based on its experience with the tracking task. This suggests that the animal develops an internal model of display properties which is used to determine when a new response is required.

Notes: Summary Cross-reinnervations were effected between the extensor digitorum longus and soleus muscles in the cat hind limb. At the same time dorsal root section or ganglionectomy was performed over segments L6-S1. Completeness of the deafferentation was subsequently confirmed either by dissection or by dorsal root recording. The isometric and forcevelocity properties of the muscles were measured. In animals with a unilateral cross plus deafferentation the conversion of the contractile properties of the normally slow-twitch soleus to those resembling a fast-twitch muscle was typical of that seen with an intact afferent supply. In cats with a bilateral cross-reinnervation and unilateral deafferentation there was no significant difference in the degree of transformation between the two sides. It is concluded that at least for the conversion of a slow-twitch to a fast-twitch muscle afferent feedback does not play a major role.

Notes: Summary Contralateral corticofugal projections from visual cortical areas to thalamic nuclei were demonstrated in the cat using anterograde transport of tritiated proline. Thalamic nuclei receiving projections from contralateral visual cortex include both subdivisions of the lateral-posterior nucleus, the posterior nucleus of Rioch, and the posterior nuclear complex.

Notes: Summary The localization and morphology of spinal respiratory motoneurones (phrenic and intercostal) were studied in the cat by retrograde labelling using Horseradish Peroxidase (HRP), at different stages of postnatal development. At birth, the distribution of the phrenic and intercostal motoneurones in the cervical and thoracic ventral horn, respectively, is similar to that observed in adult animals. At birth, the phrenic and intercartilaginous motoneurone somata have respectively 60% and 40% of their adult volume, appearing much more developed than the motoneurones involved in the motor control of limbs. During postnatal development, the phrenic and intercartilaginous motoneurones undergo a characteristic sagittal elongation without evident modification along their transverse axes. From birth, the ratio of the somatic volume to that of its corresponding motor column markedly decreases inside of the phrenic column compared to the data obtained in the limb's muscle motor columns by other authors. Similar determinations in intercostal motor columns give intermediate values between those obtained from the phrenic column and from the motor system. These results indicate that the motoneurones innervating the respiratory muscles have some specific features of development.

Notes: Summary The ascending connections from the brainstem to the dorsal division of the lateral geniculate nucleus were examined using retrograde transport of horseradish peroxidase. Labelled cells were identified in a variety of structures, including the nucleus of the optic tract (NOT), the posterior pretectal nucleus (NPP), the superior colliculus (SC), the parabigeminal nucleus (PBN), the midbrain reticular formation (MRF), locus coeruleus and nucleus sub-coeruleus, the substantia nigra (SN), and parts of the raphe complex. The projections from NOT, NPP, MRF, LC and PBN were all bilateral in origin. The most intense labelling was observed in the nucleus of the optic tract and the superior colliculus. Colliculo-geniculate cells were located primarily in the superficial gray lamina II1 and II2 of Kaneseki and Sprague (1974), but sparse labelling was also observed in lamina II3 and in statum opticum (lamina III). Consistent with the report of Harrell et al. (1982), these cells represent a morphologically diverse population, which includes stellate cells, granule cells, and both vertical and horizontal fusiform cells. A similarly diverse population of cell types contributes to the geniculate projection arising from NOT. These results confirm and extend earlier descriptions of the brainstem projections to the cat LGNd, and serve to emphasize the diversity of brainstem influences over the geniculate.

Notes: Summary Extracellular and intracellular recordings were made from spinocerebellar tract neurones of the central cervical nucleus (CCN) in C1–C3 segments of the anaesthetized cat. These neurones were identified by antidromic activation from the cerebellar peduncle. Stimulation of the ipsilateral dorsal root elicited extracellular spikes or EPSPs with a monosynaptic latency in almost all CCN neurones in the same segment (segmental input). Late excitatory effects were also observed in about one third of CCN neurones. The monosynaptic EPSP was occasionally followed by an IPSP. The excitatory input from the dorsal root to CCN neurones was extended over several segments for some CCN neurons (extrasegmental input). Monosynaptic excitation was evoked in CCN neurones after stimulation of dorsal neck muscle nerves as well; i.e. splenius (SPL), biventer cervicis and complexus (BCC), rectus capitus dorsalis, and obliquus capitus caudalis. Thresholds for this excitation were near the threshold of the nerve, suggesting that it originated from group I fibres. The component of excitation added after strong stimulation of neck muscle nerves would be attributed to group II fibres. When a CCN neurone received excitatory input from the nerve of one muscle, it was generally not affected by stimulation of other nerves in the same segment. Such muscle specificity of segmental input was the principal pattern of connexion of neck muscle afferents with CCN neurones. In some cases, however, excitatory convergence from SPL and BCC nerves onto single CCN neurones or excitation from the SPL nerve and inhibition from the BCC nerve were also observed. Nearly half of the CCN neurones received input from one muscle nerve of the same segment and not from the afferent of the same muscle of different segments, indicating a segment specificity of input. In the remaining CCN neurones, weaker excitatory effects were induced from afferents of different segments as well. In such extrasegmental effects, inputs to CCN neurones from caudal segments predominated in frequency over those from rostral segments. The origin of extrasegmental input was generally confined to the same muscle. Low threshold muscle afferents from the SPL and BCC were intraaxonally stained with HRP. The collaterals of the stained fibre distributed branchlets and terminals to the CCN, laminae VII, VIII, and motor nuclei. Two fibres responding to local muscle prodding or stretch showed a similar morphology. The findings indicated that muscle spindle afferents from primary endings projected to the CCN.

Notes: Summary Spinocerebellar tract (SCT) neurones in and around the central cervical nucleus (CCN) were physiologically identified by antidromic activation of these cells on stimulation of the cerebellum. Among the Spinocerebellar tract cells thus identified, those ascending the contralateral spinal funiculi were found in the CCN and ventralwards, whereas those ascending the ipsilateral funiculi existed mostly dorsal to the CCN partly overlapping with crossed cells in the nucleus. Mapping sites from which CCN cells were antidromically activated showed that axons of the CCN-SCT cross at the same segment, ascend the ventral funiculus initially, the lateral funiculus at rostral C1 and the lateral border of the medulla to reach the cerebellar peduncle, enter the cerebellum mainly via the restiform body but possibly also via the superior peduncle. Systematic mapping of stimulation within the cerebellum indicated that the CCNSCT projects to the medial part of the anterior lobe and the posterior lobe bilaterally. Projection to lobules I–II was found in almost all CCN-SCT cells examined. Three fourths of CCN-SCT cells projected to the posterior lobe, as revealed by less extensive mapping. Mapping of axonal regions of the same single CCN-SCT cells showed that they project multifocally in the cerebellum, where projection to lobules I–II was common and that to other areas varied with individual cells. Conduction velocites decreased within the cerebellum probably as the result of repeated branching. Mossy fibre responses evoked on stimulation of the C2 dorsal root in cats with the transected dorsal funiculi were shown to be mediated mostly via the CCN-SCT. Mapping the field potential showed that the response was by far the largest in lobules I–II. This suggested that the terminals provided by the CCN-SCT are the densest in these lobules.

Notes: Summary Endogenous peroxidase-like activity was investigated with a combined light and electron microscopical technique in 15 cats. The lateral cervical nucleus, the dorsal column nuclei, and segments C6 and L5 of the spinal cord were incubated with diaminobenzidine-tetrahydrochloride (DAB) or tetramethylbenzidine (TMB). After histochemical reaction with DAB a considerable amount of activity was found in nerve cells, astrocytes and pericytes. The neuronal labelling was mainly located in mitochondria of axon terminals and in dendrites whereas the astrocytic and pericytic activity was found in cytoplasmic dense bodies. The quantity of stained structures differed considerably between the animals. In TMB reacted tissue endogenous peroxidase-like activity was only sparsely seen. It was found mainly in frozen sections, in which the neuropil and perivascular structures sometimes contained granules and irregular filaments. The significance of the findings is discussed in relation to observations in tracer studies using horseradish peroxidase.

Notes: Summary Horizontal vestibulo-ocular reflex (VOR) and optokinetic nystagmus (OKN) were studied before and after lesions within the accessory optic system (AOS) in the cat. Post-lesion retinal input to the AOS was evaluated using the autoradiographic technique. Unilateral lesion of the lateral terminal nucleus of the AOS (LTN) and the resulting retinal deafferentation of the medial terminal nucleus of the AOS (MTN) induced a spontaneous nystagmus in the dark whose slow phase was directed ipsilaterally to the lesion. VOR gain was reduced for both directions with a maximal decrease for stimulation directed ipsilaterally to the lesion. OKN gain obtained for both directions of binocular stimulation was decreased, mainly when the stimulus was directed contralaterally to the lesion. After two postoperative weeks, spontaneous nystagmus disappeared and the VOR symmetry recovered simultaneously. A symmetrical OKN was only observed after one month. In spite of the known visual selectivity for vertical direction in LTN-MTN cells, the results of this study support a functional involvement of these nuclei in horizontal VOR and OKN.

Notes: Summary The response properties of cat horizontal canal afferents (N = 81) were characterized by three parameters: their long time constants (τ), low frequency gain constants (G1), and middle frequency gain constants (Gm). An average value of each of these parameters was calculated for each of eight animals and comparisons were made across animals. There were significant differences between individual animals in their average values of τ and Gm. There was also a significant negative correlation between τ's and Gm's. An animal with a larger average τ tended to have a smaller average Gm. We also used anatomic data on membranous canal duct diameter from the literature to independently estimate the potential effect of interanimal anatomic variability on the predicted range of τ and Gm values in a population. We then compared the data from our 81 afferents with the predictions from the anatomic data.

Notes: Summary In anaesthetized cats (chloralose-urethan) the effects of brief tetanic electrical stimulation (50 to 100 ms) of the mesencephalic central gray matter and reticular formation on the inspiratory on-switch were studied during the expiratory (E) phase on the gross and unitary activities of phrenic, laryngeal inspiratory and laryngeal expiratory nerves. On the inspiratory laryngeal and phrenic nerves, stimulation elicited a short latency gross response concomitant with the train: the inspiratory Primary Response (Prim.R.) which is followed by an inspiratory Patterned Response (Patt.R.) of longer duration which corresponded to the inspiratory on-switch. The Patt.R. generally appeared from the Prim.R. within a latent period (Silent Phase: Sil.P.) as long as 100 ms. On the expiratory laryngeal nerve, stimulation elicited a brief activation (expiratory Prim.R.) concomitant with the beginning of the inspiratory laryngeal Prim.R. and which rapidly stopped as the latter continued during the stimulus train. The inspiratory Prim.R. corresponded to a simultaneous activation of both early and late (so defined during their spontaneous discharge) inspiratory motoneurones. The laryngeal motoneurones were more strongly activated than the phrenic ones. During the inspiratory Patt.R. all the phrenic motoneurones presented a recruitment delay earlier, compared with the spontaneous one, whereas the recruitment drastically changed from an inspiratory laryngeal motoneurone to another. Thus, the two pools of motoneurones presented different properties of activation. During the inspiratory Sil.P. no concomitant expiratory laryngeal activation was observed when most of the inspiratory motoneurones were inactive. As some inspiratory laryngeal motoneurones did not stop firing, the existence of some central respiratory neurones exhibiting a similar persistent activity and subserving the inspiratory on-switch mechanisms may be hypothesized.

Notes: Summary Ascending projections from the nucleus of the brachium of the inferior colliculus (NBIC) in the cat were studied by the autoradiographic tracing method. Many fibers from the NBIC ascend ipsilaterally in the lateral tegmentum along the medial border of the brachium of the inferior colliculus. At midbrain levels, fibers from the NBIC end in the superior colliculus, the pretectum, the central gray and the peripeduncular tegmental region bilaterally with ipsilateral predominance. NBIC fibers to the superior colliculus are distributed densely to laminae VI an III throughout the whole rostrocaudal extent of the colliculus. In the pretectum, NBIC fibers terminate in the anterior and medial nuclei and the nucleus of the posterior commissure. NBIC fibers to the dorsal thalamus are distributed largely ipsilaterally. Many NBIC fibers end in the dorsal and medial divisions of the medial geniculate body, but few in the ventral division. The NBIC also sends fibers to the suprageniculate, limitans and lateralis posterior nuclei and the lateral portion of the posterior nuclear complex; these regions of termination of NBIC fibers constitute, as a whole, a single NBIC recipient sector. Additionally, the NBIC sends fibers to the centralis lateralis, medialis dorsalis, paraventricular and subparafascicular nuclei of the thalamus.

Notes: Summary Four cats labyrinthectomized shortly after birth (DELAB) exhibited the classical vestibular syndrome and recovery, while their motor development was otherwise unimpaired. As adults, they were tested for visual vestibular substitution in a locomotor task with either orientation requirements (tilted platforms) or balance requirements (narrow platforms). Visual motion cues or static visual cues were controlled using normal or stroboscopic lighting, or darkness. Measurements of the average speed of locomotion showed that: Although all cats increase their speed when more visual cues become available, a marked deficit occurs in darkness only in the DELAB cats. With either vestibular cues alone or static visual cues alone, cats are able to reach the same level of performance in the tilted platform test, which suggests a total visual-vestibular interchangeability in orientation. DELAB cats perform very poorly in the narrow rail test. When continuous vision is allowed in the narrow rail test the DELABs' performance rises but does not match that of the control group. A specific deficit in balance for the DELAB group is thus reduced by normal continuous vision as compared to stroboscopic vision, suggesting a significant, though imperfect, substitution of motion visual cues for the missing dynamic vestibular cues. Dynamic visual cues play only a minor role in most situations, when locomotory speed is high. This results support the view that both the vestibular and the visual system can subserve two distinct functions: dynamic information may stabilize the stance in narrow unstable situations, during slow locomotion. and static orientation cues may mainly control the direction for displacement. Possible interactions between head positioning and body orientation in the DELAB cats are discussed.

Notes: Summary Twenty-nine pigmented offspring of an innately esotropic female cat exhibited varying deficits in the number of binocular cells recorded in area 17 of the visual cortex as compared to 12 normal cats. Misalignment of the two eyes in these cats was found in the awake as well as in the paralysed state. Pupillography combined with measurements of visual disparity yielded abnormal esotropia of up to 8.4° under paralysis, which corresponds to an abnormal convergence of the freely moving eyes of up to 14° (average 7.4°). In the majority of animals cortical binocularity was found reduced by the two eyes controlling independent sets of separate units (U-shaped ocular dominance distribution) whereas in 7 cats the reduction was due to a partial loss of one eye's influence. The proportion of monocular units correlated with the degree of crossover of the visual axes (r = 0.73). Anatomical investigation of the retinofugal projections revealed normal appearance in three previously recorded cats in which more than 50% of cortical units had been monocularly driven. The small angles of esotropia and the “normal” appearance of eye position judged by the pupillary positions in the orbit of these cats, might suggest that we found an animal model for microstrabismus.

Notes: Summary Previous experiments have shown that the ERG response to alternating gratings vanishes gradually within 4 months after transection of the optic nerve, changes begin after 2–3 weeks. The response to gratings of low spatial frequencies deteriorates earlier than the response to gratings of high spatial frequencies (Maffei and Fiorentini 1981). Quantitative analysis of ganglion cell sizes in retinal wholemounts shows that ganglion cell shrinkage and ganglion cell loss begin at three weeks in the periphery of the retina, particularly in the temporal retina. The same morphological alteration subsequently becomes apparent also in the area centralis and the nasal retina, respectively. The main and early cell loss occurs among medium sized ganglion cells, supposedly the beta-cells. Among the alpha-cells only shrinkage is observed up to two months postoperatively. Light- and electron microscopic examination of cross sections through the retina show that pathological changes are restricted to the innermost layers.

Notes: Summary Evidence that glutamate acts as a neuro-transmitter in vestibular nerve fibers was sought (1) by electron microscope radioautographic identification of the uptake sites of [3H]-glutamic acid after incubation of slices of cat vestibular nuclei, and (2) by measuring changes in sodium-dependent high affinity glutamate uptake in nerve endings containing homogenates from normal and deafferented vestibular nuclei 8 to 11 days after unilateral vestibular nerve lesion. Electron microscopic radioautography revealed that glutamate had been taken up by numerous nerve endings projecting over the whole vestibular nuclear complex. The biochemical approach indicated that after section of the vestibular nerve, a significant decrease in high affinity glutamate uptake occurred in the vestibular nuclei, which lost their exclusively ipsilateral projection. This decrease varied from one area of the deafferented vestibular nuclei to another, reaching −58% in the lateral area of the central part corresponding to the ventral lateral vestibular nucleus and the rostral part of the descending vestibular nucleus. It is concluded that glutamate (or aspartate) is used by the vestibular nerve fibers as a neurotransmitter in the vestibular nuclei.

Notes: Summary (1) The “fictitious” scratch reflex was evoked in decerebrate curarized cats by pinna stimulation. Activity of neurons of the ventral spinocerebellar tract (VSCT) from the L4 and L5 segments of the spinal cord as well as of neurons of the spinoreticulo-cerebellar pathway (SRCP) from the lateral reticular nucleus of the medulla oblongata was recorded. Cooling and destruction of different parts of the lumbo-sacral enlargement of the spinal cord were performed. (2) Cooling of the L5 or L6 segment abolished the rhythmic activity in the greater part of the spinal hindlimb centre but did not affect the generation of rhythmic oscillations in the remaining (rostral) segments of the lumbo-sacral enlargement. Under these conditions, neither the rhythmic activity of VSCT neurons located rostral to the thermode nor that of SRCP neurons changed. (3) A normal rhythmic activity of SRCP neurons also persisted after destruction of grey matter in the L3 and L4 segments. It can be concluded that activity of these neurons is independent of whichever part of the enlargement generates rhythmic oscillations. (4) From these observations a hypothesis is advanced that the main content of signals conveyed by the VSCT and SRCP to the cerebellum is the information regarding activity of the generator of rhythmic oscillations that is located in the L3-L5 spinal segments.

Notes: Summary Neurons in the parietal region of the cerebral cortex, projecting to the ipsilateral distal forelimb area of the motor cortex (area 4γ) were identified in the cat brain using the horseradish peroxidase (HRP) retrograde tracing method. After making microinjections of HRP into the distal forelimb area of the motor cortex, clusters of HRP-labeled cell bodies were observed in different regions of the ipsilateral parietal cortex. In particular these clusters of labeled cells were found in areas 5a, 5b and 7. The area 5a cluster is formed from closely packed irregularly-shaped cells, the area 5b cluster is made up of dispersed medium-sized pyramidal cells, while area 7 contains a cluster of widely dispersed small pyramidal cells. Typically, labeled cell bodies were found in lamina III of cortex. Labeled cell bodies were neither observed in the contralateral cortex nor in the visual cortex (areas 17, 18 and 19). Since parietal cortex receives projections from primary somatosensory and visual cortex, the projections from parietal to motor cortex may well form the neural substrate for the processing of convergent sensory information used in voluntary movements.

Notes: Summary Modifications have been made in Mesulam's method for labelling neurons by retrograde transport of horseradish peroxidase, with tetramethylbenzidine as chromogen, with the object of increasing the extent of labelling of dendrites and axons. A procedure was devised specifically for studying spinomedullary and medullospinal tract systems, involving implanting easily-made HRP-agar pellets into areas of controlled damage in particular spinal fascicles, and sealing the site of implant with cyanoacrylate glue. Lesions of other fascicles were often made to limit transport to the implanted fascicle. Fourth-order dendrites were regularly labelled over long (30 cm or more) transport distances: axons were also labelled over this whole distance, often allowing exact study of the initial course of particular axons. Controls in both cat and rat showed that the uptake of HRP under these circumstances occurred almost wholly from the region of axonal damage at the site of implant which can be characterized histologically.

Notes: Abstract Treatment of cats with acrylamide, either 7.5 or 15 mg/kg IM, once a day for 10 days, resulted in increases of 31 and 47% in the phospholipid content of sciatic nerve, respectively, from a control level of 41.1±2.7 mg/kg wet weight. Determination of the distribution of individual phospholipids indicated no significant differences between control cats and those receiving a cumulative dose of 150 mg/kg acrylamide. In a separate experiment, cats were treated with the 150 mg/kg dose of acrylamide and the sciatic nerve was divided into proximal and distal portions at the level of the triceps surae nerve. Significant increases in phospholipid content were observed in both the proximal and distal portions of peripheral nerve of the acrylamide-intoxicated cats. This effect was present even when the phospholipid content was expressed in terms of total protein, dry weight or total lipid. Total weight of nerve segments, however, was significantly decreased in the neuropathic animals. The data are consistent with a focal degeneration of axons with relative sparing of phospholipids.

Notes: Abstract The responses of neurons in area 17 were tested as a function of various stimulus parameters. The thresholds of individual cortical neurons were at contrasts between 0.01 and 0.1 (increment of 0.5×10−1 cd/m−2 on a background of 3 cd/m−2), the dynamic ranges were 1.0–2.0 log units of increment, and all cells showed a response decrease at increments above a certain maximum (supersaturation response). The averaged contrast/response curve for all neurons was S-shaped in the logarithmic plot, had a dynamic range of 2.5 log units, reached its maximum at a contrast of 0.75 and supersaturated above this level. The contrast/ sensitivity curves changed their slope under different stimulus conditions. They became flatter when the non-dominant eye was stimuated as compared to dominant eye stimulation or when the stimulation was done at a non-optimal orientation or direction, and they became steeper when both eyes were stimulated. But the maximum was reached at the same contrast and supersaturation was seen above maximum contrast no matter whether a cell was stronlgy (e.g. binocular stimulation at optimal orientation) or weakly excited (non-dominant or non-optimal orientation stimulation). After normalization, the averaged population contrast/response curves were virtually identical at all stimulus conditions. It was concluded, that range as well as maximum and supersaturation of cortical contrast/response curves are determined before the input reaches the cortex, and that the cortical cells summate, essentially, linearly. The findings furthermore demonstrate that the supersaturation of the cortical input must be due to subtractive inhibition, and that the same is true for the orientation sensitive inhibition in the cortex itself. Both, the peripheral contrast and the cortical orientation dependant inhibition cannot be explained by multiplicative inhibition. The fact, that the responses of neurons depend on many variables relativates their significance for feature representation.

Notes: Summary By the use of scanningand transmission electron microscopy, the possible sources of errors in interpretation of the microcirculation of the pancreas can be reduced in comparison to the classical India-ink injection method. Sphincter-like structures in the capillary wall of the cat pancreas are established by pericytes. These sphincters encircle the junctional zones between the endocrine and exocrine capillaries. They are assumed to be regulatory structures of blood flow and to regulate indirectly hormone secretion according to demand.

Notes: Summary The caudal portion of Reissner's fiber was examined by scanning electron microscopy (SEM) in the spinal cord of the cat and rabbit. In some preparations of both species the fiber displayed in the sinus terminalis of the central canal either stump-like terminations or structural modifications such as knot-like swellings and convolutions. In the same area homogeneous material could also be found, which obviously originated from the disintegrating fiber.

Notes: Summary Endings of four β skeletofusimotor axons in a spindle of the cat tenuissimus muscle were examined in semithin (1-μm thick) and ultrathin transverse serial sections. Two (dynamic) β axons terminated on the nuclear bag1 intrafusal muscle fiber and on extrafusal fibers of the dark type. Two (static) β axons terminated on the nuclear chain intrafusal fibers and extrafusal fibers of the intermediate type. The degree of indentation of axon terminals into the muscle surface, thickness of the sole plate and extent of folding of subjunctional membranes differed among intrafusal and extrafusal terminations of the same axon. Endings of β axons on the bag1 and chain fibers were also morphologically dissimilar. Motor axons may not determine ending morphology. Rather the form and structure of a β bag1 or chain ending may be determined by the type of intrafusal fiber on which the ending lies and the ending's distance from the primary sensory axon.

Notes: Abstract There is in vision research a general unwillingness to classify or define visual cortical cell types, particularly new cell types, outside the classical simple/ complex dichotomy. Cells lacking clear-cut characteristics are, therefore, considered simple by some authors and complex by others. The present unsatisfactory state has largely arisen because of the absence of any rigorous, generally accepted, classification scheme of visual cortical neurons. Actually the present two classification schemes of visual cortical neurons, that is the Hubel and Wiesel and the Bishop schemes, are generally considered to be not comparable since the former is based on the cell qualitative static-field properties as revealed by hand-held stationary flashing stimuli, whereas the latter is based on the cell quantitative dynamic-field plotting properties as revealed by moving light stimuli. Since receptive fields lacking clear-cut characteristics of simple and complex cells have been observed in area 18 of the cat as well, all the receptive field types of this area have been classified either qualitatively or quantitatively using both the Hubel and Wiesel and the Bishop classifying procedures. It has been observed, at least as far as simple cells are concerned, that the two schemes are not antithetic but, on the contrary, equivalent if averaging procedures are taken into consideration.

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: Summary The spontaneous activity of primary vestibular neurons was studied during postnatal development in the cat. Activities were categorized as regular, intermediate and irregular on the basis of the coefficient of variation. At birth, few regularly firing units were found while the percentage of intermediate and irregular units was high. During development, the percentage of units meeting the criterion of regularity increased steadily with age. At the same time the number of intermediate and irregular units decreased. The average resting rate of all categories of unit showed an increase in firing from birth up to the adult stage, i. e., around the second postnatal month. The mean firing rate of regularly firing units was always higher than the two other categories throughout all the stages of development. These results were compared with similar work performed in the rat.

Notes: Summary The unmyelinated terminal regions of extensor muscle Ia afferent fibres were stimulated electrically near lumbar motoneurones in anaesthetised cats using 300 μs pulses of less than 1 μA passed through the central NaCl barrel of seven barrel micropipettes. Such terminations were identified by anodal blocking factors of less than four and the latency of the antidromic impulse recorded in the appropriate peripheral muscle nerve. Although the effects of microelectrophoretically administered GABA were occasionally complex, the most consistent finding was a reduction in termination threshold followed by an increase. Both this reduction in threshold by GABA, and that produced by tetanic stimulation of low threshold flexor afferents (PAD) were diminished by microelectrophoretic bicuculline methochloride. This GABA antagonist alone elevated the threshold of some terminations but did not reduce the depolarizing action of either potassium or L-glutamate. Furthermore, since reductions in threshold by GABA, but not by either potassium or L-glutamate, were associated with a decrease in PAD, GABA appears to increase terminal membrane conductance. Since neither GABA nor bicuculline methochloride influenced the threshold or afferent depolarization of non-terminal regions of Ia fibres, these results are consistent with the function of GABA as a depolarizing transmitter at gabergic axoaxonic synapses upon the terminals of Ia afferent fibres synapsing with motoneurones.

Notes: Summary Cells in the cat superior colliculus which project to the ventral and dorsal lateral geniculate nuclei (VLG and DLG) have been labeled by retro-grade transport of horseradish peroxidase (HRP). We studied the depth, area, and morphology of each labeled neuron quantitatively. Our measurements show that the projection neurons to both VLG and DLG vary in laminar position, size, and morphology. Labeled cells projecting to both nuclei were concentrated within the superficial gray layer, but were also scattered through the optic layer and, after DLG injections, in the intermediate gray layer as well. Labeled cells in both groups varied greatly in size, ranging from 49–344 μm2 cross-sectional area (mean 143 μm2) for the VLG group and from 31–398 μm2 (mean 165 μm2) for the DLG group. The labeled cells also varied in morphology after both VLG and DLG injections. The majority had a granule or vertical fusiform morphology. There were fewer with a stellate morphology and almost none with a horizontal morphology. At least three types of superior colliculus cells thus appear to project to the ventral and dorsal lateral geniculate nuclei. These cell types likely give rise to distinct functional channels to these nuclei.

Notes: Summary Spino-olivary projections from segments C1 and C2 were examined in 17 cats using autoradiographic methods and in nine cats using the method of retrograde horseradish peroxidase (HRP) transport. Injections of 3H-leucine at the junction of the C1–C2 segments produced anterograde terminal labelling in two regions of the contralateral inferior olive, one in the rostromedial half of the dorsal accessory olive (DAO), the other in the caudal half of the medial accessory olive (MAO). Projections to the rostromedial DAO were best demonstrated when tracer labelled the ventromedial part of the dorsal horn, while projections to the caudal MAO were strongly labelled by injections in both the lateral and medial parts of the intermediate grey matter. Injections of HRP into the region of the inferior olive led to retrograde marking of cells in both regions of the contralateral spinal cord implicated by autoradiographic studies to have spino-olivary projections. Dense groupings of small rounded or fusiform cells were labelled contralaterally on the medial aspect of the dorsal horn in C1 and C2, while medium-sized multipolar cells were more sparsely distributed throughout intermediate laminae of C1-C5. Olivary projections from dorsal column nuclei were also examined and compared to those of spinoolivary projections. Injections of 3H-leucine into n. gracilis and cuneatus led to terminal labelling in three olivary regions, including the rostral DAO, the caudo-lateral DAO and the caudal MAO. Projections from the DCN to the rostral DAO and the caudal MAO overlapped with regions of projection from upper cervical segments although the territories occupied by DCN and upper cervical projections were not identical. Amino acid injections which were confined to n. cuneatus gave rise to terminal labelling in only the rostromedial DAO.

Notes: Summary After injections of horseradish peroxidase (HRP) into various parts of the superior colliculus (SC) in 14 cats, retrogradely labeled neurons were found in parts of all deep cerebellar nuclei. The present study demonstrated that there are three main origins of the cerebellotectal projections in regard to the locations of the cell bodies: (1) the caudal half approximately of the fastigial nucleus (NM) including the subnucleus medialis parvocellularis (SMP), (2) the ventral and lateral parts of the posterior interpositus nucleus (NIP), and (3) the ventral part of the dentate nucleus (NL) including the subnucleus lateralis parvocellularis (SLP). The pathways and terminations of these projections have also been shown autoradiographically. Thus, fibers from NM crossed within the cerebellum and terminated in the intermediate and deep gray layers of the bilateral SC. Fibers from NIP and NL passed within the superior cerebellar peduncle, which crossed in the tegmentum (“decussation” of the peduncle) and ended in the two layers of the contralateral SC. In addition, some cerebellofugal fibers were found to terminate in the nuclei interstitialis of Cajal and Darkschewitsch, as well as in parts of pretectum and thalamus. The tecto-ponto- (and olivo-) cerebellotectal loop (cf. Kawamura 1980) has been established morphologically and it is briefly commented on in correlation with the propagation of the teleceptive (optic and acoustic) impulses.

Notes: Summary The aim of this study was to determine the differences between the monocular and binocular segments of the visual cortex in three cats by means of stereological procedures. The cytoarchitectonic images of both segments are described. The thickness of layers in both segments are slightly different. The following results have been obtained. 1. The nerve and glial cell densities are significantly smaller in the monocular segment than in the binocular one. 2. The mean projection area of the neurons is significantly (p〈0.1%) larger in the monocular segment than in the binocular one. Consequently, the mean perikaryon volume in the monocular segment amounts to about one and a half of that in the binocular segment. 3. A two-way variance analysis of neuronal densities and perikaryon sizes shows a significant difference (p〈0.1%) between both segments. 4. The perikaryon volume fraction of the monocular segment is slightly larger than that of the binocular one. 5. The perikaryon size distributions of both segments are different. The shape of the size distributions within the layers vary in both segments. The results are in accordance with the Y-X-W-classification of nerve cells in the visual system. Semi-automatic sterological procedures are capable of detecting distinct functional areas in the brain which are difficult to distinguish visually.

Notes: Summary The uptake of tritiated γ-aminobutyric acid (3H-GABA) in the oculomotor nucleus of the cat was studied, using light and electron microscopic examination of radioautograms after intracerebral in vivo administration of the amino-acid. A glial uptake by oligodendrocytes was seen together with a neuronal uptake of the tracer in a certain type of axon terminals found in synaptic contact with both dendrites and soma, some of them exhibiting all the ultrastructural features of motoneurons. Previous neurochemical, electrophysiological and immunocytochemical studies indicate that GABA might well be the inhibitory neurotransmitter in the vestibuloocular reflex arc. The present results show that a morphological substrate exists for the presumed postsynaptic GABAergic inhibition of ocular motoneurons, at least in the oculomotor nucleus of the cat.

Notes: Summary Behavioral and neuroanatomical consequences of a thiamine-deficient diet, combined with the application of a thiamine-antagonist (pyrithiamine) were investigated in the cat. Eight cats (the experimental group) were subjected to a vitamine-B1-poor diet until they developed neurological symptoms (epileptic attacks, ataxia, gait disturbances), while 24 cats were fed normally and served as control group. Immediately following the appearance of neurological signs, a high dose of thiamine was given to the cats of the experimental group; they were then allowed to recover for ten days. Thereafter the performance in learning an alternation task in a T-maze was tested and compared with that of the control group. Behaviorally, the cats of the experimental group manifested drastically retarded acquisition rates in the learning task compared to the cats of the control group. Neuroanatomically, damage was found in the brains of each of the cats in the experimental group; this damage consisted mainly of enlarged ventricles, hemorrhages, neuronal loss and gliosis. Those regions most consistently affected were the periaqueductal gray, the inferior colliculi and the mamillary nuclei. The thalamic mediodorsal nucleus was affected to a minor degree in three cats only. Four cats manifested damage in the hippocampal formation. No damage was found in the cerebellum. Most of the damaged neuroanatomical loci resemble those found in patients with a Wernicke-Korsakoff syndrome.

Notes: Summary We recorded from single cells in the cat's visual cortex to quantitatively evaluate (1) the reliability of subjective assessments of ocular dominance (101 cells) and (2) the stability of ocular dominance over time (25 cells). We found that the correlation between subjective and objective measures of this variable was poorer than expected, and was worst for cells with low overall response strengths. This result appears to reflect variability in the subjective assessment procedure. For the second part of the study, we recorded from single cortical cells of 5-week-old kittens, and made repeated objective measurements of ocular dominance over time. Twenty-four of the twenty-five cells examined were quite stable in ocular dominance for periods so long as 8 h. One unit was encountered which showed substantial progressive shifts in ocular dominance over time.

Notes: Summary Single unit activity of 842 cells has been recorded in cat visual cortex and analyzed with respect to vestibular induced, and spontaneous saccadic eye movements performed in the dark. This study has been done in awake, chronically implanted cats, subsequently placed in “acute” conditions to achieve the precise retinotopic mapping of the cortical areas previously investigated. In areas 17 and 18, respectively, 27% and 24% of the cells tested were influenced by horizontal saccadic eye movements in the dark (E. M. cells). In the Clare-Bishop area, the proportion of E. M. cells was 12%, while only 2% of such cells were found in areas 19 and 21. The distribution of E.M. cells in areas 17 and 18 with respect to retinotopy showed that E.M. cells were more numerous in the cortical zones devoted to the representation of the area centralis (38% in area 17, 27% in area 18) than in the zones subserving the periphery of the visual field (17% and 12%, respectively). Two of the characteristics of E. M. cell activations appear dependant on the retinotopic organization. First, a larger number of E.M. cells presenting an asymmetry in their responses to horizontal saccadic eye movements in opposite directions (directional E.M. cells) were encountered in the cortical representation of the peripheral visual field. 53% of E. M. cells recorded in area 17 and 71% in area 18 were directional in the cortex corresponding to the peripheral visual field. This percentage was of 23% and 25% respectively in the cortex devoted to area centralis. Second, E.M. cells were found to have a latency from the onset of the saccade systematically larger than 100 ms (i.e, they discharged at, or after the end of the eye movement) if they were located in the cortical representation of the area centralis, while E.M. cells related to the peripheral visual field displayed a wider range of latencies (0–240 ms). Results obtained in Clare Bishop area, although limited to the representation of the peripheral visual field, were quantitatively and qualitatively similar to those observed in the homologous retinotopic zones of areas 17 and 18. It is concluded that an extra-retinal input related to oculomotor activity is sent to the cat visual cortex and is organized, at least in areas 17 and 18, with respect to the retinotopic representation of the visual field. These data support the hypothesis of a functional duality between central and peripheral vision and are discussed in the context of visual-oculomotor integration.

Notes: Summary The effects of mechanical stimulation (tap) on single unit activity of Deiter's neurons were analysed in walking cats decerebrated at the premammillary level. Deiters' neurons projecting to the ipsilateral cervical, but not to the lumbosacral, spinal cord (C-Deiters' neurons) were identified by antidromic activation, cerebellar stimulation, and localization of the neurons. During each unperturbed cycle of quadrupedal locomotion, most C-Deiters' neurons showed two frequency modulation peaks in their impulse discharges: one (A peak) in the late swing (E1) or the early stance (E2) phase, the other (B peak) in the late stance (E3) or the early swing (F) phase, of the ipsilateral forelimb. The A peak started to rise shortly before the ipsilateral forelimb was placed. When mechanical perturbation was applied during locomotion to the paw dorsum of the left forelimb (LF) in its stance phase, the ongoing LF stance phase shortened and the simultaneous swing phase of the right forelimb (RF) shortened. Accordingly, in the RF, extensor activity in the swing phase to place down the limb occurred earlier than in unperturbed step cycles. The same LF tap induced a marked enhancement of impulse discharges in C-Deiters' neurons on the right side (with a magnitude of 20–100 imp/s, and the shortest latency of 25 ms). This enhancement was more pronounced than that induced when the perturbation was applied to the LF during its swing phase. The latency manifested a close time relation to the RF extensor activity supporting the postulate that the increased C-Deiters' activity in the RF swing phase contributes to the earlier onset of RF extensor activity which plays an important role in maintaining alternating footfalls after perturbation.

Notes: Summary The activity of neck muscles was recorded in the alert, head-fixed cat together with the horizontal and vertical components of eye movements. Electromyographic activity of obliquus capitis cranialis and caudalis, and longissimus capitis, is closely related to horizontal eye position in the orbit both during spontaneous eye movements and vestibular nystagmus. The activity of splenius also shows this relationship but the coupling is less tight, probably because of the postural function of this muscle.

Notes: Summary Electrical activation of the ipsilateral arcuate region of the hypothalamus produced an inhibitory influence upon three separate subpopulations of cells encountered in the ventrolateral PAG. Quiescent PAG cells were classified by their response pattern to sural nerve stimulation: Type A cells displayed only a short latency discharge; whereas, Type B cells exhibited a triphasic response pattern. Arcuate nucleus stimulation dramatically reduced the evoked discharge of both A and B cell types. Type C cells represented spontaneously active PAG neurons which were less affected by arcuate nucleus activation. Systemic naloxone (5 mg/kg) reduced the degree of inhibition of only Type B neurons. Naloxone was ineffective in attenuating arcuate inhibition of Type A and C neurons. Type B neurons may represent a class of cells which are more involved in nociceptive systems and therefore are susceptible to modulation by endogenous opiate peptides.

Notes: Summary This study examines the possibility of a vestibular input to the visual cortex using chronically implanted cats subjected to horizontal sinusoïdal rotation in the dark. In areas 17 and 18 the activity of respectively 14% and 11% of units was modified by vestibular stimulation. Both non-specific and specific influences were observed. Specific influences (42% in area 17 and 33% in area 18) were similar to the types of responses recorded in the vestibular nuclei, and were encountered more frequently within the cortex subserving the peripheral visual field. Our results could provide a neurophysiological basis for some psychophysiological observations concerning visuo-vestibular interactions.

Notes: Summary The afferent projections to, and the interconnections between, four structures of the socalled limbic system were investigated in the cat. The retrograde horseradish peroxidase (HRP) technique was used to trace the origins of fibers projecting to each of these four loci. Particular emphasis was laid on tracing cortical afferents of these regions. Four injections were performed in the dorsal and two in the ventral subicular regions; six were centered within the mamillary nuclei, four within the anterior thalamic nuclei, and three within the cingulate gyrus. For each region, a number of projections were found which had apparently not been described before, at least not for the cat: For injections into the subicular regions, a hitherto unknown number of cortical afferents was detected, including labeled cells in the prefrontal and premotor fields and from large areas within the posterior parietal, temporal and occipital cortex (i.e., sensory and sensory integration cortex); numerous neurons were labeled in the anterior nuclear group of the thalamus. Injections of HRP into the mamillary nuclei revealed, aside from a strong projection from the subicular regions, frontocortical and cingulate projections to the mamillary nuclei; the mamillary nuclei also received subcortical projections from the septum, the diagonal band of Broca and from the periaqueductal gray. Following injections into the anterior thalamic nuclei, labeled cells were found in the prefrontal cortex, and to a lesser extent in lateral parts of the cortical hemisphere; subcortically, the mamillary nuclei received connections from hypothalamic areas, the periaqueductal gray, the diagonal band of Broca and the claustrum. Cingulate injections labeled cells in temporal and parietal cortical areas, in the subicular region, and also in the periaqueductal gray. Our findings reveal that each of the four injected areas receives a large number of afferents from divergent regions of the brain; of these, a considerable number is shared by each of the four injection loci. Furthermore, the present results reveal that the subiculum, the mamillary bodies, and the anterior thalamus are more strongly interconnected than previously assumed.

Notes: Summary In five, dark-reared, 4-week-old kittens the posterior two thirds of the corpus callosum were split, and a lesion comprising the intralaminar nuclei was made of the left medial thalamic complex. In addition, the right eye was closed by suture. Postoperatively, the kittens showed abnormal orienting responses, neglecting visual stimuli presented in the hemifield contralateral to the side of the lesion. Sudden changes in light, sound, or somatosensory stimulation elicited orienting responses that all tended toward the side of the lesion. These massive symptoms faded within a few weeks but the kittens continued to neglect visual stimuli in the hemifield contralateral to the lesion when a second stimulus was presented simultaneously in the other hemifield. Electrophysiologic analysis of the visual cortex, performed after the end of the critical period, revealed marked interhemispheric differences. In the visual cortex of the normal hemisphere most neurons were monocular and responded exclusively to stimulation of the open eye, but otherwise had normal receptive field properties. In the visual cortex of the hemisphere containing the thalamic lesion, the majority of the neurons remained binocular. In addition, the selectivity for stimulus orientation and the vigor of responses to optimally aligned stimuli were subnormal on this side. Thus, the same retinal signals, which in the control hemisphere suppressed the pathways from the deprived eye and supported the development of normal receptive fields, failed to do either in the hemisphere containing the thalamic lesion. Apparently, experience-dependent changes in the visual cortex require both retinal stimulation and the functioning of diencephalic structures which modulate cortical excitability and control selective attention.

Notes: Summary We examined the characteristics of postsynaptic potentials (PSPs) produced in antidromically-identified medial gastrocnemius (MG) α-motoneurons by electrical stimulation of low threshold (〈 3×T) distal limb cutaneous afferents in the sural (SUR) nerve in adult cats anesthetized with α-chloralose, together with the effects on SUR PSPs of supraspinal conditioning stimulation of the contralateral red nucleus (RN) and pyramidal tract (PT). In the majority of MG motoneurons, SUR afferents with electrical thresholds 〈 1.5×T produced early excitatory synaptic potentials (EPSPs) with minimum central latency of about 2.0 ms, suggesting activation of a trisynaptic segmental pathway with two interposed interneurons. Such early EPSPs were often detectable with stimuli 〈 1.2×T, as determined by recording the compound action potential in the sciatic nerve and from the first appearance of the N1 wave of the cord dorsum potential. Inhibitory synaptic potentials (IPSPs) were regularly produced by SUR volleys of only slightly greater strength (often as low as 1.3×T) and these had minimum central latencies of about 3.0 ms (about 1.0 ms longer than the earliest EPSPs), suggesting a three interneuron central pathway. Repetitive stimulation of RN and PT regularly produced facilitation of both EPSP and IPSP components in the SUR response, suggesting that these supraspinal systems directly or indirectly excite some of the same interneurons that convey the SUR effects to MG motoneurons. When using very low strength SUR stimuli, PT conditioning produced relatively pure facilitation of the SUR EPSPs but with larger SUR volleys, PT clearly facilitated both EPSPs and IPSPs. RN conditioning produced more parallel facilitation of SUR EPSPs and IPSPs. Supraspinal control of the polysynaptic pathway producing SUR EPSPs is of particular interest because of earlier evidence that this pathway is differentially distributed to motoneurons of fast twitch versus slow twitch MG motor units.

Notes: Summary Electromyographic (EMG) activity associated with rapid voluntary limb movements exhibits a characteristic “three burst pattern”. The first burst is in the agonist muscle (AG1), the second is in the antagonist (ANT) and the third is again in the agonist (AG2). The present study was undertaken to determine whether ANT and AG2 reflect preprogrammed commands or responses to stretch consequent upon limb displacement. To answer this question EMG activity of agonist and antagonist muscles was examined in cats performing a tracking task. To dissociate centrally programmed muscular events from their intended mechanical consequences, isometric and anisometric conditions were presented in either a predictable or unpredictable sequence. A torque motor was used to control limb trajectory and to impose passive angular displacements. Whereas AG1 was present under both isometric and anisometric conditions, ANT and AG2 required limb displacement and were time locked to movement parameters. ANT occurred within 15 ms following the onset of acceleration. Its magnitude varied linearly with this parameter and inversely with AG1. Passive displacements stretching the antagonist elicited responses with similar latencies and greatest magnitude for a given acceleration. AG2 was only present in underdamped movements with terminal oscillations and typically occurred when the position reached its peak and the velocity recrossed zero. Its magnitude was a function of both limb deceleration and of intended force. The data indicate that both ANT and AG2 represent responses to muscles stretch whose amplitudes are modulated by descending commands. Reciprocal mechanisms operating at a spinal level could account for the reduction of the antagonist response as a function of intended force. The increased sensitivity of late stretch responses in the agonist with higher intended forces is compatible with motoneuron facilitation by tonic descending commands. It is proposed that the stretch evoked responses function to dampen terminal oscillations which ensue from rapid displacement of the mass of the limb against elastic forces of muscle and soft tissue.