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PubMed1979

Disparity tuning and binocularity of single neurons in cat visual cortex.

Activity from single neurons in the visual cortex of anaesthetized and paralyzed cats were recorded in response to monocular and binocular stimuli of different retinal disparities. Three different types of disparity sensitive neurons were found, characterized by (1) a response maximum near zero disparity, (2) a response minimum near zero disparity, and (3) an asymmetric disparity sensitivity. Usually, neurons of the first type receive about the same monocular input from the two eyes; the other disparity sensitive neurons respond better to monocular stimulation of one eye as compared to the other. The results closely resemble those obtained recently in the rhesus monkey.

Animals↗

PubMed1976

Age dependence of the effect of squint on cells in kittens' visual cortex.

The period of susceptibility of the visual cortex of kittens to the effect of squint is limited to the first three postnatal months. The reduction of binocularity found in these kittens as reflected by the distribution of neurons according to their ocular dominance is especially emphasized in animals operated on between the ages of 4-7 weeks in comparison to animals operated on between the ages of 8-11 weeks. The proportion of monocularly dominated neurons within the first three postnatal months is significantly (0.05 greater than p greater than 0.025) reduced with age. Similar effect on cortical neurons was found for animals who were under the influence of squint for 6 weeks or 15 months and for animals with wide range of deviation angles.

Age Factors↗

PubMed1975

[Effect of visual deafferentiation on the ultrastructure of synapses of the rat visual cortex].

Electron microscopic study and quantitative analysis of the visual cortex synapses in 14, 30 and 60-day-old rats were performed after bilateral enucleation of newly-forn rats. A great amount of synapses of other functional systems was shown to be functioning in the area striata in addition to the synapses formed by specific visual afferents. Alterations in the synapses of the area striata of blind rats are developing gradually, achieving the greatest pronouncement in 60-day-old rats. These changes develop according to the type of atrophic process in connection with dysfunction. The atrophic alterations of the synapses were found both in axo-somatic and axo-dendritic synapses on the dendrite trunks and on the thorns. The alterations of synapses being concentrated in layer IV. The quantitative ratio of different kinds of atrophied synapses in the cross-section of the visual cortex was different suggesting the following conclusion about the distribution of the visual afferents. In layers I and III the visual afferents formed mostly axon-thorn contacts and less amount of axo-somatic and axo-dendritic synapses on the dendrite trunks. In layer IV they mainly formed axo-somatic and axo-thorn synapses and less amount of axo-dendritic ones on the dendrite trunks. In layers V and VI they mainly contact with the dendrite trunks and with the nervous cell bodies and more rarely with thorns.

Afferent Pathways↗

PubMed1991

The development of ventral tegmental area (VTA) projections to the visual cortex of the rat.

The development of the ventral tegmental area (VTA) projections to the rat visual cortex was studied with the wheat germ agglutinin-horseradish peroxidase (WGA-HRP) retrograde tracing technique. Large injections of WGA-HRP in the visual cortex of newborn, early postnatal, and adult rats resulted in a substantial number of retrogradely labelled neurons in the VTA showing the same distribution pattern at all ages examined. Contrary to other reports, labelled cells were never found in the pars compacta of the substantia nigra but occasionally were seen in the contralateral VTA near the midline. These neurons showed a continuous growth from the day of birth to the end of the second postnatal week, when they acquired morphological features comparable to the adult; they subsequently showed a substantial decrease in soma size. The present results clearly demonstrate that there exists a substantial mesocortical projection to the rat visual cortex which arises exclusively from the VTA. This projection is already established at birth, but the neurons which give rise to it appear morphologically immature during the first two postnatal weeks.

Animals↗

PubMed1990

Elaborate organization of visual cortex in the hamster.

We have studied the organization of visual cortex in the hamster by analyzing and correlating the distributions of callosal and striate-extrastriate connections. Our results show that, in lateral extrastriate cortex, callosal connections form an elaborate pattern which delineates at least 3 regions poor in callosal connections. These regions receive projections from striate cortex which are distributed into multiple separate fields. Two additional striate-projection fields were observed in medial extrastriate cortex, and another field was often observed near the posterolateral border of primary somatosensory cortex. All striate recipient fields are reciprocally connected with striate cortex. The patterns of callosal and striate-extrastriate connections in the hamster are similar, although not identical, to the corresponding patterns in rats and mice. Our results provide evidence that the organization of visual cortex in the hamster is highly elaborate, and suggest that extrastriate cortex is subdivided into multiple visual areas.

Animals↗

PubMed1979

Direct evidence for recurrent inhibition in sliced brain preparation of the cat's visual cortex.

To reveal the recurrent inhibitory circuit in the visual cortex, a depolarizing current was applied through a glass microelectrode to an impaled cell in an in vitro slice of the visual cortex obtained from a cat anesthetized with pentobarbital. The cell reported here produced inhibitory postsynaptic potentials (IPSPs) following single spikes or bursts of spikes which were elicited by intracellularly applied current. This observation indicates that IPSPs have been mediated by the recurrent inhibitory circuit via axon collaterals of the impaled cell.

Action Potentials↗

PubMedDate not supplied

[Non-specific facilitating influences on the responses of rabbit visual cortex neurons].

A study was made of neuronal responses in the rabbit visual cortex to patterned visual stimuli and their change during non-specific activation reaction. Non-specific activation while only slightly affecting the background neuronal activity, enhances the responses of most units to patterned visual stimuli. A comparison of responses with a different degree of inhibition participation shows that the depression of inhibitory processes may act as a mechanism of facilitation of the responses during non-specific activation. After facilitated responses evoked by the action of the stimulus during non-specific activation, the neurones retain a state of enhanced excitability. Repetition of stimuli not attended with non-specific activation leads to the diminution of excitability. The possible connection of the indicated effects with extinction processes is discussed.

Animals↗

PubMed1992

Beta-adrenergic receptors: astrocytic localization in the adult visual cortex and their relation to catecholamine axon terminals as revealed by electron microscopic immunocytochemistry.

It has long been recognized that noradrenaline, the most abundant catecholamine within the visual cortex, plays important roles in modulating the sensitivity of cortical neurons to visual stimuli. However, whether or not these noradrenaline effects are confined to a discrete synaptic specialization or mediated by diffuse modulation of a group of synapses has remained an issue open for debate. The aim of this study was to examine the cellular basis for noradrenaline action within the visual cortex of adult rats and cats. To this end, I used electron microscopic immunocytochemistry to examine the relationship between (1) catecholamine axon terminals and beta-adrenergic receptors (beta AR), which, together, may define the effective sphere of noradrenaline modulation; and then (2) these putative sites for catecholamine modulation and axospinous asymmetric junctions where excitatory neurotransmission is likely to dominate. Antibodies against beta AR were used at light and electron microscopic levels on the visual cortex of rat and cat. Rat visual cortex was also labeled simultaneously for beta AR and the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH), to determine the ultrastructural relationships between catecholamine terminals and beta AR. Immunoperoxidase labeling revealed that beta AR404, a polyclonal antibody directed against the C-terminal tail of hamster lung beta AR (beta 2-type), recognized astrocytic processes predominantly. In contrast, beta AR248, a polyclonal antibody directed against the third cytoplasmic loop, recognized neuronal perikarya as observed in previous studies. Dual labeling for beta AR404 and TH revealed that catecholamine axon terminals that contained numerous vesicles formed direct contacts with astrocytic processes exhibiting beta AR404 immunoreactivity. However, some catecholamine axon terminals that lacked dense clusters of vesicles were positioned away from beta AR404-immunoreactive astrocytes. Frequently, beta AR-immunoreactive astrocytic processes surrounded asymmetric axospinous junctions while also contacting catecholamine axon terminals. These observations support the possibility that, through activation of astrocytic beta AR, noradrenaline modulates astrocytic uptake mechanism for excitatory amino acids, such as L-glutamate. Astrocytic beta AR might also define the effective sphere of catecholamine modulation through alterations in the morphology of distal astrocytic processes and the permeability of gap junctions formed between astrocytes.

Animals↗

PubMed1987

Biochemical evidence for glutamate and/or aspartate as neurotransmitters in fibers from the visual cortex to the lateral posterior thalamic nucleus (pulvinar) in rats.

The effects of visual cortex ablation on several neurotransmitter parameters in the lateral thalamic nucleus (pulvinar) in rats have been investigated. We found a 57% decrease in high affinity uptake of D-[3H]aspartate in the pulvinar after ablation of the ipsilateral visual cortex. The KCl-evoked release of exogenous D-[3H]aspartate and endogenous glutamate were decreased by 33 and 37%, respectively. Moreover, the contents of endogenous glutamate and aspartate were decreased by 35%, each. The glutamate decarboxylase and choline acetyltransferase activities and the contents of other amino acids were not affected by the lesion. Our biochemical data indicate that glutamate and/or aspartate may be transmitters in the fibers from visual cortex to pulvinar in rats.

Animals↗

PubMed1977

Responses of single cells in cat visual cortex to prolonged stimulus movement: neural correlates of visual aftereffects.

1. The activity of single cortical cells in area 17 of anesthetized and unanesthetized cats was recorded in response to prolonged stimulation with moving stimuli. 2. Under the appropriate conditions, all cells observed showed a progressive response decrement during the stimulation period, regardless of cell classification, i.e., simple, complex, or hypercomplex. 3. The observed response decrement was shown to be largely cortical in origin and could be adequately described with an exponential function of the form R = Rf +(R1-Rf)e-t/T. Time constants derived from such calculations yielded values ranging from 1.92 to 12.45 s under conditions of optimal-stimulation. 4. Most cells showed poststimulation effects, usually a brief period of reduced responsiveness that recovered exponentially. Recovery was essentially complete in about 5-35 s. 5. The degree to which stimuli were effective at inducing response was shown to have significant effects on the magnitude of the response decrement. 6. Several cells showed neural patterns of response and recovery that suggested the operation of intracortical inhibitory mechanisms. 7. A simple two-process model that adequately describes the behavior of all the studied cells is presented. 8. Because the properties of the cells studied correlate well with human psychophysical measures of contour and movement adaptation and recovery, a causal relationship to similar neural mechanisms in humans is suggested.

Anesthesia, General↗

PubMed1992

Proportion of glutamate- and aspartate-immunoreactive neurons in the efferent pathways of the rat visual cortex varies according to the target.

Immunohistochemistry, with antisera directed against glutamate (Glu) or aspartate (Asp), was combined with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) histochemistry to examine the distribution, morphology, and proportions of Glu- and Asp-containing neurons that give rise to corticofugal and callosal projections of the rat visual cortex. WGA-HRP injections in the dorsal lateral geniculate nucleus resulted in retrograde labelling of small and medium-sized cells throughout layer VI of the visual cortex. Of these cells, 60% were also Glu-immunoreactive and 61% Asp-positive. WGA-HRP injections in the superior colliculus labelled large and medium-sized neurons in the upper portion of layer V of the visual cortex. Of these cells, 46% were also stained for Glu and 66% for Asp. Injections in the pontine nuclei resulted in retrograde labelling of cells in the deeper part of cortical layer V. Retrogradely labelled cells, which were also immunoreactive for Glu or Asp, were large pyramidal cells. Corticopontine neurons, which were also Glu-positive, accounted for 42% of the total number of WGA-HRP labelled cells, whilst for Asp-positive neurons this percentage was 51%. Finally, after injections in the visual cortex, retrogradely labelled small and medium-sized cells were found throughout layers II-VI in the contralateral visual cortex. Of these neurons, 38% were also labelled for Glu while 49% were also Asp-immunoreactive. The present results demonstrate that substantial proportions of projection neurons in the rat visual cortex are immunoreactive for Glu or Asp, suggesting that these excitatory amino acids are the major transmitters used by the cortical efferent systems examined. Furthermore, the proportions of these immunoreactive neurons in the efferent pathways vary according to the target.

Animals↗

PubMed1992

[Visual recognition processes in monkeys and their neuronal correlates in the visual cortex: the effect of an M-cholinoreceptor blocker].

Unit activity was studied in the visual cortex prior to and after amyzyl administration in monkeys trained for delayed visual differentiation of different colour stimuli. The data obtained suggests that the cholinergic mechanisms of the visual cortex are involved in the visual recognition and seem to play different functional roles at different stages of the behaviour.

Acoustic Stimulation↗

PubMed1986

Visual cortex controls retinal output in the rat.

The first objective of the present investigation was to shed more light on corticofugal influences on the retina by providing an analysis of the type and proportion of retinal ganglion cells that are affected by cooling the visual cortex in rats. The second question was to determine if the pretectum participates in functional cortico-retinal relationships. In urethane-anesthetized and paralyzed hooded rats, axonal activity of retinal ganglion cells was recorded with glass micropipettes at optic chiasm level. Units were classified as ON, OFF, suppressed-by-light and concentric. The visual cortex was inactivated by cooling its surface with a 4 mm2 steel probe using the Peltier effect. The pretectum was blocked with microinjections of 50 to 100 nanoliters of cobalt ions, lidocaine hydrochloride or KCl. The inactivations and recoveries at both sites were monitored by simultaneously recording evoked field potentials. Interrupting corticofugal impulses caused modifications of the evoked discharge pattern in all types of cells. The concentric type was the group least affected by cortical cooling. A common trend emerged suggesting that cooling of the visual cortex led to an enhancement of the initial evoked excitation. This was often followed by an enhanced post-excitatory inhibition. The Pearson coefficient allowed us to measure the degree of similarity between two histograms. When all data were pooled, a weak correlation between control and test histograms (r = 0.29, N = 56) was found, while the control and recovery patterns averaged a correlation of more than twice that size (r = 0.68). In a second series of experiments, the pretectum and visual cortex (VC) were simultaneously inactivated. It is shown that both sites summed their influence and acted synergistically upon the pattern of ganglion cell responses. The results strongly suggest that the visual cortex exerts a major control over the response pattern of thirty percent of retinal ganglion cells, and that the pretectum participates in the functional relationships between visual cortex and retina in rats.

Animals↗

PubMed1974

Cell structure and function in the visual cortex of the cat.

1. The organization of the visual cortex was studied with a technique that allows one to determine the physiology and morphology of individual cells. Micro-electrodes filled with the fluorescent dye Procion yellow were used to record intracellularly from cells in area 17 of the cat. The visual receptive field of each neurone was classified as simple, complex, or hypercomplex, and the cell was then stained by the iontophoretic injection of dye.2. Fifty neurones were successfully examined in this way, and their structural features were compared to the varieties of cell types seen in Golgi preparations of area 17. The majority of simple units were stellate cells, whereas the majority of complex and hypercomplex units were pyramidal cells. Several neurones belonged to less common morphological types, such as double bouquet cells. Simple cells were concentrated in layer IV, hypercomplex cells in layer II + III, and complex cells in layers II + III, V and VI.3. Electrically inexcitable cells that had high resting potentials but no impulse activity were stained and identified as glial cells. Glial cells responded to visual stimuli with slow graded depolarizations, and many of them showed a preference for a stimulus orientation similar to the optimal orientation for adjacent neurones.4. The results show that there is a clear, but not absolute correlation between the major structural and functional classes of cells in the visual cortex. This approach, linking the physiological properties of a single cell to a given morphological type, will help in furthering our understanding of the cerebral cortex.

Action Potentials↗

PubMed1991

Development of the laminar distribution of thalamocortical axons and corticothalamic cell bodies in the visual cortex of the wallaby.

The distribution of afferents from the dorsal lateral geniculate nucleus (LGNd) and the lateral posterior nucleus (LP) and of cell bodies projecting to these nuclei has been studied in the visual cortex of the wallaby (Macropus eugenii) throughout development to determine how the characteristic laminar distribution of afferents and efferents of the mature cortex is achieved. Young are born after 26-28 days of gestation and do not open their eyes until around 140 days after birth. Horseradish peroxidase conjugated to wheatgerm agglutinin was injected in the visual thalamus in adults and in pouch young aged from 22 days after birth, just after thalamic axons first reach the visual cortex, to 118 days, when cortical lamination resembles the adult. From 22 to 65 days, the developing visual cortex consists of a marginal zone (MZ), cortical plate (CP), and intermediate zone (IZ) including the superficial subplate (SP), subventricular zone, and ventricular zone. There is a thin compact cell zone (CCZ) at the top of the CP and below it a less densely packed region that increases in thickness with age. Retrogradely labelled cells in two bands were first seen at 40 days, one in the CCZ and the other at the base of the CP. Two bands of cells were seen at all subsequent times if the injection covered both LGNd and LP, and by 76 days, these cells were located within cytoarchitectonically recognizable layers V and VI. Anterograde label prior to 45 days was distributed densely and evenly throughout the IZ and the CP up to the CCZ. Label in MZ was first seen at 25 days and was substantial by 54 days. Anterograde label than became gradually reduced in the IZ, whereas in the CP it remained evenly and densely distributed until 82 days. At this age, coincident with the emergence of layer IV, label within the CP first showed variations in density and by 99 days was concentrated over layer IV and, to a lesser extent, over layer VI. By 118 days label resembled the adult after injections covering both LGNd and LP, with label concentrated in layer I, IV, and VI with a less dense projection to lower layer III and upper layer V. There is a relatively earlier initial ingrowth of axons into the visual cortex in the wallaby and throughout development thalamocortical axons appear to be more widely distributed in the depth of the visual cortex than has been demonstrated for placental mammals.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗

PubMed1984

[Afferent connections of the visual cortex in the albino mouse].

The afferent connections of the visual cortex of the albino mouse have been studied with the aid of the enzyme Horseradish peroxidase (HRP). Ipsilateral HRP-positive cells have been found in areas 17, 18a, 18b and the temporal cortex; in the contralateral cortex, they were located in areas 17, 18a and in the temporal cortex, the greatest number of labeled cells being situated near the 17/18a border. Apart from the Nucleus dorsalis corporis geniculati, more thalamic nuclei project to the visual cortex; the Nucleus lateralis thalami, pars posterior contains regularly positive cells, whereas other nuclei (Nucleus lateralis thalami, Nucleus medialis thalami, pars lateralis, Nucleus ventralis thalami, pars lateralis and pars medialis) only in some cases show labeled cells. Sporadically, a few labeled cells were observed in the Nuclei medialis and lateralis tractus optici, Nucleus praetectalis thalami and the Nucleus centralis medialis. The afferent connections from the brain stem have not always been visualized. The most frequent afferent connections come from the Nucleus dorsalis tegmenti pontis, followed by the Nucleus reticularis tegmenti pontis and the Nucleus Locus coerulei. Occasionally, a few HRP-positive cells were found in the Nucleus ventralis tegmenti, Nucleus raphe dorsalis, Nucleus parabrachialis lateralis and in the Nucleus centralis superior. The morphology of the projecting neurons in different centres was studied and compared after HRP-filling and after Golgi-impregnation.

Animals↗

PubMed1986

A transient pyramidal tract projection from the visual cortex in the hamster and its removal by selective collateral elimination.

During the early postnatal development of the neocortex in rats there is an axonal projection from the occipital cortex (which includes the visual cortex) to the spinal cord which is subsequently completely removed through a process of selective collateral elimination. In order to determine whether a similar phenomenon occurs during the development of the hamster cortex, we have injected the retrogradely transported fluorescent dye Fast Blue (FB) into the pyramidal decussation of hamsters at various ages. In adult hamsters such an injection results in a band of labeled neurons confined to layer V and to about the rostral two-thirds of the neocortex; no labeled cells are seen in the occipital cortex. However, a similar FB injection made during the first postnatal week results after a 4-day survival in a continuous band of FB-labeled layer V neurons spread throughout the tangential extent of the neocortex, including the occipital cortex. A similar continuous band of FB labeled layer V neurons is seen throughout the tangential extent of the neocortex including the occipital region in hamsters injected during the first postnatal week but allowed to survive until the fourth week (i.e., after the restriction of the widespread neonatal pattern has occurred). Injections of the anterograde tracer wheat germ agglutinin conjugated to horseradish peroxidase made into the occipital cortex, or for comparison, into more rostral cortical regions in hamsters ranging in age from neonates to adults, reveal that the extension of pyramidal tract axons is staggered along the anterioposterior axis of the cortex such that axons originating from the posterior regions lag behind those arising from more rostral areas. The transient occipital projection appears to reach a maximum around the end of the first postnatal week: a large number of labeled occipital axons is seen in the medullary pyramidal tract, and some of these can be followed through the pyramidal decussation and into the dorsal funiculus of the spinal cord. Injections into the occipital cortex on P16 label only a few fibers in the medullary pyramidal tract, and none is labeled in hamsters injected as adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

The length summation properties of layer VI cells in the visual cortex and hypercomplex cell end zone inhibition.

Layer VI of the visual cortex has been considered to be dominated by cells with very long receptive fields, typically summing to 8 degrees or more. We have re-examined this issue in a series of experiments in which the length tuning profiles of layer VI cells in the cat visual cortex have been quantitatively determined. Responses were assessed to optimally oriented bars of light of varying length drifted over the receptive field. The lengths were varied on a randomised interleaved sequence. Although our data confirm the presence of long field cells in layer VI, only 24% of a population of 119 cells had fields greater than 6 degrees in length. Fields greater than 8 degrees were only seen in 17% of cells. 61% of the population of cells had fields showing summation to 4 degrees or less with a mean length of 2.8 degrees (+/-0.15 sem). In this "short field" group, 18% had fields of 1 degrees or less. We observed 7 cells with rapid initial spatial summation up to 1 degree, followed by clear end zone inhibition. It has been recently suggested on the basis of localised inactivation experiments, that layer VI cells with long (greater than 8 degrees) fields may provide the drive to inhibitory interneurones in layer IV generating hypercomplex cell end zone inhibition. This observation is difficult to equate with evidence indicating that hypercomplex cell end zone inhibition reflects a mechanism showing maximal summation at lengths in the region of 2.8 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗