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PubMed1975

[Interhemispheric relations of the cat visual cortex following unilateral polarization of the secondary visual area].

In 40 anesthetized cats, evoked potentials following light flashes during unilateral polarization of the secondary cortical visual area with DC anode (2-10 mcA) were studied in symmetrical centers of the 17th and 18th fields. Four phases of interhemisphere interrelationships between the 18th field's symmetrical centers were shown: 1 -- extracallosal phase of synergic depression; 2 -- callosal phase of dominant interrelationships; 3 -- callosal phase of synergic depression; 4 -- callosal-extracallosal phase of dominant interrelationships. In symmetrical centers of the 17th field, the only 1 extracallosal phase of synergic depression was observed during which the transcallosal modulation of nervous processes occurred. The data obtained are interpreted from the standpoint of the role of dominanta in interhemisphere interrelationships.

Animals↗

PubMed1989

Noradrenergic control of ocular dominance plasticity in the visual cortex of dark-reared cats.

In the visual cortex of cats which had been dark-reared for several months since the time before natural eye opening, a cortical infusion of 6-hydroxydopamine (6-OHDA), a noradrenaline (NA)-related neurotoxin, partially suppressed a usual shift in ocular dominance following brief monocular lid suture, causing a significant loss of binocular cells. This partial shift in ocular dominance (U-shaped histogram) was also observed typically in the control hemisphere of cats which were subjected to dark-rearing for more than a year. Furthermore, the expected shift in ocular dominance following monocular deprivation was blocked by a direct cortical infusion of D,L-metoprolol, a selective beta 1-adrenergic receptor antagonist. The blockade was not obtained by D-metoprolol, a biologically inert stereo-isomer, under the comparable condition. In contrast, exogenous L-NA gave rise to an obvious shift in ocular dominance toward the non-deprived eye. The present results suggest that the NA-beta 1 adrenoreceptor system was necessary to maintain the ocular dominance plasticity in the visual cortex of dark-reared cats.

Animals↗

PubMed1985

Plasticity in cat visual cortex restored by electrical stimulation of the locus coeruleus.

It has been proposed that the presence of noradrenaline (NA)-containing terminals and NA-related receptors within the visual cortex is necessary to maintain the high level of neuronal plasticity in the immature visual cortex of kittens. In the present study we wanted to show whether electrical stimulation of the locus coeruleus (LC), which contains the somata of these cortical NA fibers, can restore neuronal plasticity to the normally aplastic visual cortex of juvenile and adult cats. We consistently found a significant loss of binocular cells in the visual cortex of mature animals which had monocular vision for only 12 h dispersed over 6 days (2 h a day, otherwise kept in the dark) in combination with concurrent LC stimulation. This result was interpreted as indicating that endogenous NA released from NA terminals restored susceptibility to monocular vision in the mature visual cortex. We next examined how long the restored plasticity lasts in the same animals after the LC stimulation was ended. The animals revived from the first recording session were either returned to the same daily schedule of brief monocular exposure (light/dark = 2/22 h) as before, or subjected to the usual monocular lid suture and kept in a cat colony environment (light/dark = 16/8 h). The LC electrodes had been removed and no more electrical stimulation was delivered at this stage. In the animals subjected to reiteration of brief monocular exposure, the state of reduced binocularity gradually returned to normal over a period of 2-3 weeks after stopping LC stimulation. We calculated that the revived plasticity disappeared at an average rate of a 22% loss every 7 days. This result sharply contrasted with the result obtained in the animals subjected to usual monocular lid suture. In this test the state of reduced binocularity continued for at least the next 3 weeks, suggesting that the restored plasticity was sustained throughout a period of 3 weeks (longest term tested). The different results obtained in the two paradigms may be explained by the different strength of binocular imbalance in the two tests imposed on the visual cortex in which neuronal plasticity was restored partially.

Animals↗

PubMed1990

Regional distribution of binding sites for neuropeptide Y in cat and monkey visual cortex determined by in vitro receptor autoradiography.

The goal of this study was to elucidate the precise regional and laminar distribution of neuropeptide Y (NPY) binding sites in feline and primate visual cortex. By means of in vitro receptor autoradiography, NPY binding sites in primate and feline visual cortex were specifically labeled with 3H-NPY. In cat area 17, the highest density of NPY-binding sites was present in lamina I and the upper half of lamina II. The density then gradually decreased towards lamina VI. Areas 18 and 19 exhibited a similar binding site-density profile. The decrease in density from superficial to deep layers was more gradual in area 18 than in areas 17 and 19. In monkey primary visual cortex (V1), layer IVc presented a high concentration of NPY binding sites, in addition to a dense zone of binding sites in layer I. Monkey secondary visual cortex (V2) displays a similar dense zone in layer I, but lacks such high density of NPY binding sites in layer IV. Therefore, the border between primary and secondary visual cortex coincides with the abrupt disappearance of this latter high density in layer IV. In cat as well as in monkey visual cortex, no significant differences were found between regions representing central vision and those representing the peripheral parts of the visual field. Comparison of our results for NPY binding sites with the distribution of alpha 1-adrenergic receptors, as recently described by Rakic et al. (J. Neurosci. 8(10):3670-3690, 1988) for primate and Parkinson et al. (Brain Res. 457:70-78, 1988) for feline visual cortex, revealed that those two patterns are very similar.

Animals↗

PubMed1976

Effects of serial unilateral and serial bilateral visual cortex lesions on brightness discrimination relearning in rats.

In Experiment 1, rats with serial unilateral (SU), serial bilateral (SB), or one-stage bilateral (B) visual cortex lesions (areas 17, 18 and 18a) were compared in their retention of a preoperatively learned brightness discrimination. Both the first-stage and second-stage lesions for the SU and SB groups involved the same amount of cortical tissue and the same composite areas of visual field projection in primary and extraprimary visual cortex. Groups SU and SB showed substantial savings of the brightness discrimination after the completed bilateral visual cortex removals, while Group B showed a complete postoperative loss. In Experiment 2, the effects of two additional types of serial bilateral visual cortex lesions were investigated. These involved the medial and then lateral aspects of visual cortex in two stages (ML), or vice versa (LM). Once again, the serial bilateral lesion groups (SB, ML, and LM) showed substantial savings of the discrimination after the completed lesion, while Group B showed a complete post-operative loss. These results demonstrate a general advantage of serial damage over one-stage damage to visual cortex in recovery of a preoperatively learned brightness discrimination and indicate that the serial lesion effect is not specific to interhemispheric relationships.

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PubMed1988

Development of neuronal responses in cat posteromedial lateral suprasylvian visual cortex.

We studied the normal development of responses to visual stimulation among neurons in the posteromedial lateral suprasylvian (PMLS) visual cortex, an extrastriate visual cortical area in cats. Recordings were made from 495 single neurons in 19 kittens that were 2, 3, 4, 8, or 12 weeks of age, and the results were compared with those from normal adult cats. The percentage of neurons that respond to light increased from 57% in 2-week-old kittens to approximately adult values in 8-week-old kittens (81%). The strength and consistency of neuronal responses also increased with age. Nearly all of the responsive cells had well-defined excitatory receptive-field centers, and the receptive-field center sizes were similar to adults at all ages studied. However, few cells (5%) had inhibitory receptive-field surrounds in 2-week-old kittens. The incidence of surround inhibition increased to adult levels (about 40% of the cells) by 8 weeks of age, and the strength of surround inhibition also increased with age. Most cells responded best to moving stimuli in 2-week-old kittens, just as in adults. However, only about 20% of the responsive cells were direction sensitive at 2 weeks of age. The percentage of direction-sensitive cells increased gradually with age and reached approximately adult values by 8 weeks of age (74%). Once cells developed complete direction selectivity, with no response in the null direction, directional tuning width was similar to that in adults. When tested with slits of light flashed at various orientations or with spots and slits moving in various directions, few cells (8% or less) showed orientation selectivity at any age, just as in adults. Most of the cells were binocularly driven, and the ocular dominance distribution was similar to adults at all ages studied. These results indicate that many response properties of PMLS neurons are similar to those of adults as early as 2 weeks of age, soon after the time of eye opening. However, some properties show marked developmental changes. The mechanisms and sources of these changes are considered. In addition, the relevance of these results to mechanisms of compensation following early damage to visual cortical areas 17, 18 and 19 is discussed.

Aging↗

PubMed1981

Intracortical microstimulation of neurons in the visual cortex of the cat.

The response of visual cortex neurons to local intracortical microstimulation was measured in the anesthetized cat. When the recording microelectrode was very close (about 20 micrometers) to the tip of the stimulating electrode, threshold currents as low as 10 micro A were capable of firing neurons. Over a 20-fold range in distance from the site of stimulation, an 80-fold increase in threshold current was observed. The mean latency of activation for 30 neurons tested with intracortical stimulation was 2.88 +/- 0.45 msec. The majority of these cells were probably synaptically activated. The mean threshold current for these neurons was 0.55 +/- 0.12 mA (N = 30). These values were significantly smaller than the thresholds found previously when stimulating electrodes were located on the pia-arachnoid surface of the visual cortex.

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PubMed1988

The pharmacology of synapses formed by identified corticocollicular neurons in primary cultures of rat visual cortex.

Primary cultures of neurons from the visual cortex of 7-10-d-old Long Evans rats were used to study the pharmacology of synaptic transmission. Dissociated cells were grown either in mass cultures, which contained 8000-10,000 neurons, or in miniature island cultures of 50-100 cells. Prior to dissociation, cells in layer V of visual cortex that project to the superior colliculus were labeled in vivo by retrograde transport of fluorescent latex microspheres-a permanent fluorescent marker. After 2 d to 8 weeks in culture, labeled neurons were identified by epifluorescent illumination, and electrophysiological recordings were obtained from a labeled cell and, simultaneously, from a nearby unlabeled neuron in the same field of view. The 2 neurons were stimulated sequentially by current injection and the pharmacology of evoked postsynaptic potentials (PSPs) was investigated. In mass cultures, relatively few pairs of neurons from which we recorded were synaptically connected, although nearly every cell exhibited abundant spontaneous EPSPs and IPSPs. Neurons grown on island cultures generally did not exhibit spontaneous synaptic activity; however, stimulation of one of the cells in a pair frequently elicited a short-latency PSP in the follower neuron. Retrogradely labeled corticocollicular neurons produced only excitatory PSPs in follower cells, while unlabeled neurons were either excitatory or inhibitory. Three antagonists of excitatory amino acid receptors, kynurenic acid, piperidine dicarboxylic acid, and gamma-D-glutamylglycine, completely blocked EPSPs produced by labeled corticocollicular neurons, as well as EPSPs produced by nearly all of the unlabeled excitatory cells. We have previously shown that these compounds block both N-methyl-D-aspartate (NMDA)-type and non-NMDA receptors on cultured cortical neurons (Huettner and Baughman, 1986). The specific NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV) did not alter short-latency EPSPs recorded in 1 mM Mg2+, but did reduce longer-latency EPSPs polysynaptic activity. Since responses mediated by the NMDA receptor are known to be antagonized by Mg2+ (Mayer and Westbrook, 1985), we perfused cultures with Mg2+-free medium and found that the falling phase of some monosynaptic EPSPs was prolonged. Addition of APV to Mg2+-free medium reduced the duration of the falling phase of EPSPs such that they returned to the time course obtained in 1 mM Mg2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1992

Calretinin-immunoreactive neurons in the primary visual cortex of dolphin and human brains.

A new class of gamma-aminobutyric acid (GABA)ergic neurons immunoreactive to the calcium-binding protein calretinin (CR) was demonstrated in primary visual cortices of the bottlenose dolphin (Tursiops truncatus) and humans (Homo sapiens). Comparative analysis revealed several differences between dolphin and human visual cortex in the laminar distribution of CR-positive perikarya, although general typology of the immunoreactive CR-positive neurons was similar in both species. Thus, in both human and dolphin primary visual cortex almost all CR-positive neurons are non-pyramidal, either fusiform or bipolar cells, oriented with their long axis along the radial axis of the cortex. Large multipolar stellate cells were also observed in layers I and VI. The CR-positive neurons in the dolphin visual cortex are concentrated almost exclusively in layer I and, to a lesser extent, in layer II. In all other layers (IIIa, b, IIIc/V and VI) of the dolphin visual cortex CR-positive neurons were only rarely seen. In the human primary visual cortex CR-positive neurons are located mainly in layers II, III and IVa, b, c, with considerably lower densities of these cells observed in layers V and VI. CR-positive neurons in layer I of the human visual cortex are represented by Cajal-Retzius horizontal cells, whereas no such cells were seen in layer I of the dolphin neocortex. The numerical density of CR-positive neurons in the dolphin primary visual cortex is significantly lower than in the area of cortex in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1986

Control of cell number in the developing visual system. III. Effects of visual cortex ablation.

The effect of unilateral deletion of the visual cortex on early cell death and eventual cell number in various structures of the visual system was examined. At minimum, this manipulation potentially provides excess retinal afference to the superior colliculi, partially denervates the superior colliculi, reduces normal retinal terminal area and opens up potential target space for the retina and superior colliculus in those areas where they share terminal space with the visual cortex. All layers of the superior colliculus, bilaterally, showed an initial decrease in the rate of cell death relative to normal followed by an increase in cell death rates. No change in the number or distribution of cells in the retinal ganglion cell layer resulted despite a substantial loss of retinal terminal area, and a substantial alteration of the pattern of retinal central termination. These results are interpreted as evidence for two stages in normally occurring cell death, a first in which axons compete to colonize any available terminal space, and a second in which axon-to-target specificity must be matched. These results also provide evidence that the amount of target required for neuron survival is clearly variable.

Animals↗

PubMed1991

Laminar and regional distribution of galanin binding sites in cat and monkey visual cortex determined by in vitro receptor autoradiography.

The distribution of galanin (GAL) binding sites in the visual cortex of cat and monkey was determined by autoradiographic visualization of [125I]-GAL binding to tissue sections. Binding conditions were optimized and, as a result, the binding was saturable and specific. In cat visual cortex, GAL binding sites were concentrated in layers I, IVc, V, and VI. Areas 17, 18, and 19 exhibited a similar distribution pattern. In monkey primary visual cortex, the highest density of GAL binding sites was observed in layers II/III, lower IVc, and upper V. Layers IVA and VI contained moderate numbers of GAL binding sites, while layer I and the remaining parts of layer IV displayed the lowest density. In monkey secondary visual cortex, GAL binding sites were mainly concentrated in layers V-VI. Layer IV exhibited a moderate density, while the supragranular layers contained the lowest proportion of GAL binding sites. In both cat and monkey, we found little difference between regions subserving central and those subserving peripheral vision. Similarities in the distribution of GAL and acetylcholine binding sites are discussed.

Animals↗

PubMed1987

Local cortical lesions abolish lateral inhibition at direction selective cells in cat visual cortex.

Many cells in the cat visual cortex display a strong selectivity for the direction of motion of an optimally oriented stimulus. Postsynaptic inhibition has been suggested to generate this direction selectivity in simple cells, but the intracortical pathways involved have not been identified. While continuously recording from simple cells in layers 4 and 6, we have inactivated the superficial cortical layers in small regions 0.4-2.5 mm from the cortical column under study by using heat lesions, localized cooling or gamma-aminobutyric acid (GABA) microiontophoresis. When inactivation affected cortical regions retinotopically representing motion in the non-preferred direction towards the receptive field, the responses to movement in this direction increased, and the recorded cells lost direction selectivity due to loss of inhibition. Our results indicate that direction selectivity of simple cells involves asymmetric inhibition of predictable cortical topography.

Animals↗

PubMed1988

The effects of ablation of visual cortex in neonatal rabbits on the organization of retinothalamic and retinopretectal projections.

Primary visual cortex was ablated unilaterally in neonatal rabbits. Following a survival of 2-4 months, retrograde degeneration of the dorsal lateral geniculate nucleus (LGd) was assessed, and reorganization of retinofugal pathways was studied using methods of anretrograde transport of [3H]proline or of horseradish peroxidase. A complete lesion of primary visual cortex resulted in complete retrograde degeneration of the LGd with no sparing of any class of neurons. The terminations of retinofugal axons in the pretectum and thalamus were compared with those observed in normal animals. No major reorganization of ipsilateral retinofugal projections was observed in either the thalamus and pretectum ipsilateral to the ablated cortex, or in the thalamus and pretectum contralateral to the ablated cortex. However, contralateral retinofugal projections to the thalamus and to the pretectum ipsilateral to the ablated cortex were significantly different from normal. In the thalamus, the projections to the lateral posterior nucleus were expanded in area and increased in density. In the pretectum, the projections to the rostral pretectal areas were greatly increased in area, especially in the region of the olivary pretectal nucleus and posterior pretectal nucleus. However, the density of these projections was not increased relative to normal. Consideration of these results in relation to other published data on the anatomical consequences of neonatal visual cortex lesions, both in mammals which show behavioral sparing following neonatal visual cortex lesions and in mammals which, like the rabbit, show no behavioral sparing, suggests that: (1) behavioral sparing may correlate with patterns of survival or death of neurons in the thalamus and retina; and (2) reorganization of retinofugal pathways is not necessarily associated with behavioral sparing.

Animals↗

PubMed1987

Synaptic reorganization in the dorsal lateral geniculate nucleus following damage to visual cortex in newborn or adult cats.

We have studied the effects of making large lesions of visual cortex on the synaptic organization of the dorsal lateral geniculate nucleus (LGN) in the cat. Visual cortex was removed at birth in one group of cats and during adulthood in a second group. Following survival periods of 6 months to 2 years, the organization of synapses made by afferents from the retina in the LGN was investigated quantitatively with the electron microscope. In single thin sections we determined the percentage of retinal axon terminals that made synapses in the LGN, the average number of synapses made by each retinal axon terminal, and the identity of each postsynaptic process. These measurements were made separately for retinogeniculate connections in the A and C laminae of the LGN. For comparison, similar sets of measurements were made in adult cats that had been reared normally. When single thin sections from the A or C laminae of the LGN in normal cats are examined, about 60% of the axon terminals from the retina are seen to make at least one synaptic contact. These contacts can be with dendrites or F profiles or both. On average, each retinogeniculate terminal makes approximately 1.4 synapses in the plane of a single section and contacts dendrites three times as often as F profiles. In the A laminae of the LGN in cats that received a visual cortex lesion at birth or in adulthood, the percentage of retinal terminals that make synapses is the same as in normal cats. Similarly, the average number of synaptic contacts made by each retinogeniculate terminal is not changed by a lesion of visual cortex. In contrast, the number of contacts made with dendrites is reduced markedly, by about 29% after a lesion at birth and 53% after a lesion as an adult. However, these reductions are offset by compensatory increases in the number of contacts made with F profiles, and thus the mean number of contacts made by each retinogeniculate terminal is stabilized at a normal value. In the C laminae of the LGN, retinogeniculate terminals also reapportion their synaptic contacts. In cats with a lesion during adulthood, the redistribution of synapses is compensatory, as in the A laminae. When a lesion is made at birth, however, the number of new retinal contacts made with F profiles exceeds the number of dendritic contacts that are lost. As a result, each retinogeniculate terminal makes about 26% more synapses, in total, than normal.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗

PubMed1995

Differential properties of cells in the feline primary visual cortex providing the corticofugal feedback to the lateral geniculate nucleus and visual claustrum.

We have examined the responses of 141 layer VI cells in the feline visual cortex. Within this group we compared the responses of a subpopulation of cells checked for connectivity by electrical stimulation in the dLGN and the visual claustrum. The antidromically identified corticogeniculate projecting cells had relatively short receptive fields, as judged from length response curves, measured quantitatively, and were located at the "short" end of the receptive field length spectrum seen in the general population. Of the 17 corticogeniculate projecting cells, 71% were S type cells, which were typically monocular and directionally selective, with relatively long latencies following electrical stimulation. The remaining 29% were C type cells, also directionally selective, but with a wider spread of ocular dominance preferences and shorter latencies following electrical stimulation. S and C type subpopulations did not differ in their receptive field lengths. The mean receptive field length for this subpopulation was 2.2 degrees +/- 0.27, the shortest field being 1 degrees and the longest 5 degrees. The five layer VI cells activated by electrical stimulation from electrodes within the dorsocaudal (visual) claustrum all had much longer receptive field lengths than the corticogeniculate population, often 10 degrees or longer and were monocular and directionally selective S type cells. These data indicate that the information carried in the corticogeniculate stream (and that from layer VI directly to layer IV carried by axon collaterals) is relatively tightly focused in spatial terms whilst the less spatially focused, long receptive field output from layer VI projects to the claustrum.

Animals↗

PubMed1986

Spatial contrast and flicker sensitivity following medial thalamic or visual cortex lesions in hooded rats.

In rats, lesions of the medial thalamus that involve the intralaminar nuclei produce a number of visual impairments similar to those obtained with visual cortex ablation, suggesting that the former functionally disrupt visual cortex. This was tested by a direct comparison between the two lesions on spatial contrast and flicker sensitivity, using behavioural techniques. Both lesions depressed spatial contrast sensitivity, visual cortex damage more than thalamic lesions. Only medial thalamic lesions produced statistically significant changes in flicker sensitivity. This dissociation suggests that medial thalamic and visual cortex lesions are disrupting different mechanisms. Alternative explanations of the thalamic deficit are discussed.

Animals↗

PubMed1990

Spatial organization of axons in turtle visual cortex: intralamellar and interlamellar projections.

The spatial pattern of projections within turtle visual cortex was studied by using focal injections of horseradish peroxidase into visual cortex in an in vitro wholebrain preparation. Injections anterogradely filled the axons of many layer 2 neurons, which could be followed for 200-500 microns from the injection sites. Axons were typically unbranched, relatively straight, and bore small varicosities at irregular intervals. They radiated from the injection sites in all directions, but showed some preference toward orientations along the lateral-medial axis of the cortex. Earlier work (Mulligan and Ulinski, '90) had demonstrated that turtle visual cortex contains a series of isoazimuth lamellae, each representing an individual azimuth of visual space and oriented perpendicular to the rostral-caudal axis of the cortex. The present study provides evidence for intrinsic projections both along isoazimuth lamellae and between adjacent lamellae. These projections may play roles in the elaboration of wide receptive fields of cortical neurons.

Animals↗

PubMed1975

[The rat visual cortex. Cytoarchitecture and stereotactic parameters].

In the present investigation the visual cortex of the albino rat was analyzed. On the basis of cytoarchitectonic criterions we can demarced the area striata (field 17) from a medial (field 18) and lateral (field 18a) lying peristriatic area. There are differences in the cortical structure not only between the striate and peristriate areae but also between field 18 and field 18a. In this publication we also present the visual cortex in stereotaxic coordinates on the basis of the stereotaxic atlas of FIFKOVA and MARSALA. Stereotaxic informations belonging the different fields of the visual cortex of the rat are not yet known, but they are very helpful for experimental investigations in this region of the brain.

Animals↗