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At least 37 records · Page 2Linked to original sources
PubMed1990

Dark-rearing retards the maturation of astrocytes in restricted layers of cat visual cortex.

The cat visual cortex develops its mature appearance, i.e., its circuitry and neuronal morphology, during a limited period of postnatal development under the influence of visual experience. The critical period for cortical plasticity, which normally extends from the third to seventh postnatal week, can be prolonged by raising animals in total darkness. The prolongation of the critical period by dark-rearing is restricted to the cortical layers except layer IV. Besides the influence of afferent activity on the physiology of cortical cells and on the interconnectivity of thalamo-cortical afferents, visual experience has also been shown to affect the development of glial cells. The present study investigates the effects of dark-rearing on astroglial characteristics as determined by immunostaining for glial fibrillary acidic protein (GFAP) and the S-100 protein. The data reveal a retardation of astrocytic maturation in dark-reared animals, shown by a reduced presence of GFAP immunoreactivity compared to light-experienced animals. The density of astrocytic cell bodies positive for S-100 is unaffected by dark-rearing, suggesting that astroglial proliferation does not rely on afferent activity. However, punctate S-100 staining in the neuropil, which has been shown to reflect astrocytic processes, was also reduced in certain cortical layers in dark-reared animals. The effects of dark-rearing on the expression of GFAP and S-100 were restricted to the cortical layers except layer IV, i.e., those layers that reveal a prolongation of the critical period for cortical plasticity following dark-rearing. It is concluded that astrocytic maturation in the visual cortex is influenced by neuronal activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Molecular markers of neuronal subpopulations in layers 4, 5, and 6 of cat primary visual cortex.

Cat primary visual cortex has been used as an immunogen to produce monoclonal antibodies that detect subpopulations of neurons. When tested by immunofluorescence on tissue sections of areas 17 and 18, 2 of these antibodies, VC1.1 and VC5.1, outlined a rare subpopulation of neurons located mainly in layer 4 but also in layers 5 and 6. Double-labeling immunofluorescence experiments in area 17 revealed that all VC1.1-reactive cells were also VC5.1-reactive and 83% of VC5.1-reactive cells were VC1.1-reactive, suggesting that the antibodies were reacting with the same subpopulation of cells. Both antibodies labeled similar or identical subpopulations of cells in other areas of the cat CNS, including the superior colliculus, parts of hippocampus, cerebellar deep nuclei, and rostral spinal cord. Neither antibody labeled cell bodies in the lateral geniculate nucleus. In the retina, VC1.1 labeled cell bodies and processes of some horizontal and amacrine cells, whereas VC5.1 labeled only ganglion cell axons. In the cerebellar cortex, the most prominent labeling of VC1.1 was of Purkinje cells, whereas that of VC5.1 was of Lugaro cells. Immunoblotting analyses of cat cortical homogenates demonstrated that VC1.1 recognized a major polypeptide band of Mr 95,000-105,000 and additional bands of Mr 145,000 and Mr 170,000. VC5.1 recognized bands of Mr 97,000 and Mr 150,000. Subcellular fractionation and extraction studies showed that the VC1.1 antigens were integral membrane proteins preferentially located in a synaptosomal plasma membrane fraction. The VC5.1 antigens were preferentially located in a soluble cytoplasmic or extracellular fraction. The results indicate that antibodies VC1.1 and VC5.1 recognize unique epitopes in the cat CNS and define a previously unrecognized subpopulation of cells in cat visual cortex.

Animals↗
PubMed1987

Effects of corpus callosum section on functional compensation in the posteromedial lateral suprasylvian visual area after early visual cortex damage in cats.

A visual cortex lesion made in adult cats leads to a loss of direction selectivity and a loss of response to the ipsilateral eye among cells in posteromedial lateral suprasylvian (PMLS) cortex of cats. However, a visual cortex lesion made in young cats results in normal direction selectivity and normal ocular dominance in PMLS cortex. Thus cats with an early lesion demonstrate functional compensation in PMLS cortex. The present experiment determined whether the functional compensation depends upon an intact corpus callosum. Cats received a unilateral visual cortex lesion on the day of birth (day 1) or at 8 weeks of age. When the cats were adult, the corpus callosum was sectioned and 24 hours later recordings were made in PMLS cortex ipsilateral to the visual cortex lesion. Results were compared to cats with a similar lesion and an intact corpus callosum. In cats with a lesion made on day 1, a corpus callosum section did not affect receptive-field properties or ocular dominance in PMLS cortex. Therefore, functional compensation is not dependent on input via the corpus callosum in these animals. However, in cats with a lesion made at 8 weeks. a corpus callosum section resulted in a decrease in the percentage of direction-selective cells and in the percentage of cells driven by the ipsilateral eye. Despite the decrease, the percentage of direction-selective cells still was greater than in cats with an adult unilateral visual cortex lesion. Thus, while partly dependent on callosal inputs, some functional compensation for direction selectivity remains on the basis of ipsilateral inputs.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1978

[Neurons of the rabbit visual cortex with simple and complex visual fields].

The receptive filelds of orientation-selective neurons were studied in the rabbit visual cortex. Two mechanisms of the selectivity were found: the mutual inhibition between on- and off-regions of the receptive field (simple type) and the orientation-dependent inhibition within the uniform region of the receptive field. The non-selective neurons could exhibit the lateral inhibition within the uniform region of the receptive field also. It is supposed that both "simple" and "complex" cells originate from the non-selective units.

Animals↗
PubMed1988

Functional influence of areas 17, 18, and 19 on lateral suprasylvian cortex in kittens and adult cats: implications for compensation following early visual cortex damage.

The aim of the present study was to investigate the mechanisms of physiological compensation that is seen in the posteromedial lateral suprasylvian (PMLS) cortex of cats that received visual cortex (areas 17, 18, and 19) damage early in life. The strategy was to compare the response properties of PMLS neurons just after visual cortex damage (before any compensation has occurred) with the properties of PMLS neurons in normal cats and cats with long-standing visual cortex damage. Fourteen animals (aged 8 weeks, 18 weeks, 26 weeks, or adult) received a unilateral visual cortex lesion and recordings were made from ipsilateral PMLS cortex within about 24 h. An additional 4 adult cats were studied within either 24 or 3 h of a bilateral visual cortex lesion. Results from these animals were compared with results from normal cats and cats with long-standing visual cortex damage studied previously in this laboratory. At all ages studied, an acute visual cortex lesion reduced the percentage of direction-sensitive cells in PMLS cortex from nearly 80% in normal cats to about 20% after the lesion. In 8- and 18-week-old kittens, nearly all of the remaining PMLS cells responded best to stimulus movement but were not direction sensitive. In 26-week-old and adult cats, the remaining cells were divided between those that responded to movement without a directional preference and those that responded as well to stationary flashed stimuli as to moving stimuli. The presence of receptive-field surround inhibition was not affected significantly by an acute lesion at any age. In addition, few PMLS cells were orientation selective to elongated slits of light in cats with an acute lesion, just as in normal cats. The ocular dominance distributions of PMLS neurons also were normal following an acute visual cortex lesion at all ages studied. These results suggest that the influences of areas 17, 18, and 19 on the response properties of PMLS neurons are the same when the properties first reach maturity as in adult cats. The results also suggest that the mechanisms of physiological compensation for an early visual cortex lesion differ for different response properties. Compensation of direction sensitivity and orientation selectivity (an anomalous property) develops de novo after the early lesion. In contrast, compensation of ocular dominance appears to be due to the maintenance of a preexisting property that is present immediately after the lesion. Thus, plasticity after early visual cortex damage represents multiple developmental changes in the remaining visual pathways.

Aging↗
PubMedDate not supplied

Ketamine-xylazine anaesthesia blocks consolidation of ocular dominance changes in kitten visual cortex.

In the visual cortex of mammals, response properties of single neurons can be changed by restricted visual experience during early postnatal development. Covering one eye for four to eight hours when kittens are at the peak of the sensitive period is sufficient to weaken the influence of the occluded eye on cortical neurons resulting in a noticeable shift of ocular dominance towards the open eye. The underlying changes in synaptic connections do not occur so readily when a kitten is anaesthetized and paralysed. We report here that an ocular dominance shift is prevented in alert kittens that receive repeated brief monocular exposures when these are followed by ketamine-xylazine anaesthesia. This retrograde effect on cortical plasticity suggests that the process by which synaptic activity is converted into structural changes has been disturbed.

Animals↗
PubMed1992

Visually evoked oscillations of membrane potential in cells of cat visual cortex.

In response to visual stimulation, cells of the cat visual cortex fire rhythmically at frequencies between 30 and 60 hertz. This rhythmic firing can be synchronized among cells in widespread areas of the visual cortex. The visual stimulus conditions under which this process occurs suggest that the synchronization may contribute to the integration of information across broadly displaced parts of the visual field. An intricate mechanism must control the regularity of firing and its synchronization. In vivo whole-cell patch recordings from cells in area 17 have now shown that robust oscillations of membrane potential underlie the regularity of firing seen extracellularly. In the cells studied, the characteristics of the oscillations of membrane potential suggest that such oscillations are produced by rhythmic activity in synaptic inputs. These rhythmic synaptic inputs form the most likely mechanism for the synchronization of activity in neighboring cortical cells.

Animals↗
PubMed1979

[Heterogeneity of a neuron population with complex receptive fields in the visual cortex of costs].

Visual responses of the striate complex cells to stimuli orientation, direction and velocity of movement were studied in awakening, unanesthetized cats. "Complex" cells were divided into four groups according to the response characteristics which were obtained using a stationary slit, moving light spot and moving oriented stimulus. The first group units response characteristics suggest the presence of the orientation selectivity mechanism in their receptive field organization, the fourth group--the direction selectivity mechanisms, the second and third groups--the presence of both mechanisms. It is supposed that there are two separate mechanisms for coding the orientation and direction of the stimulus movement in the neuronal structures of the visual cortex.

Animals↗
PubMed1989

Patterns of connections in rat visual cortex.

The definition of visual areas is one of the central problems in visual cortex research. Rodent extrastriate cortex offers a striking example of the complexity of this issue, in that different parcelation schemes identify within it from 2 to as many as 13 separate visual areas. In the experiments reported here, patterns of connections within rat visual cortex were studied in an effort to better define its organizational layout. The experimental paradigm used consisted of the following steps: first, the pattern of callosal connections was revealed in vivo with the fluorescent tracer bisbenzimide. Then, using the callosal pattern as a landmark, single injections of WGA-HRP were placed at various sites in striate and extrastriate cortex. Subsequently, the relation between the tangential distribution of ipsilateral corticocortical connections, the callosal connections, and the borders of striate cortex were examined in the flattened cortex preparation. The experiments revealed widespread, patchy connections within rat visual cortex. These connections appeared to reflect 3 organizational trends. First, neighboring sites were more extensively connected than distant ones. Second, extrastriate sites receiving common striate cortex inputs tended to be interconnected. Finally, projections from opposite poles in striate cortex tended to form interdigitating patterns of connections in regions of overlap. Altogether these trends suggest that the extrastriate band adjoining striate cortex has a single, global map organization. However, within the global map, a clear modular organization was evident, which appeared to correspond to the multiple visuotopic representations reported for this region. Based on its location, and some organizational similarities. it is suggested that the global map may constitute the rat homolog of area V2 in cat and monkey.

Animals↗
PubMed1990

Change in the pattern of behavioural specialization of neurons in the motor cortex of the rabbit following lesion of the visual cortex.

In order to find out whether damage of the visual cortex (area 17) of the brain results in a functional reorganization of the motor cortex, experiments were carried out with freely moving rabbits performing a food acquisition task in an experimental cage. Two rabbits served as controls, while in three rabbits the visual cortex was bilaterally damaged. Analysis of the activity of 575 neurons in the control and operated rabbits after the recovery of the original instrumental food acquisition behaviour revealed a marked difference in the behavioural specialization of the neurons in the motor cortex of two operated rabbits compared with the control animals. Although the same types of units as in the control rabbits could be found in the operated rabbits (M neurons activated in relation to body and limb movements, S neurons activated in relation to food seizure and L neurons activated in relation to learned food acquisition task), the number of S units was about half of that in the controls and the number of L units about double. The relative number of activations of the neurons in the operated rabbits was significantly less frequent during the food seizure and more frequent during the learned behaviour. This difference indicates a change in the pattern of behavioural specialization of the neurons in the motor cortex due to the damage of the visual cortex. In this reorganization, the motor cortex became more like (but not identical to) visual and limbic cortices that normally contain noticeably more L neurons than the motor cortex. The number of neurons activated in relation to the behaviour in the operated rabbits, as compared with the control animals, was smaller in the upper and larger in the lower layers of the motor cortex. This may indicate recruitment of new neurons from the lower cortical layers.

Animals↗
PubMed1978

Physiological consequences for the cat's visual cortex of effectively restricting early visual experience with oriented contours.

1. The early visual experience of nine cats was restricted to viewing horizontal or vertical lines inside opaque goggles. 2. When the kittens were 3-4 mo old, extracellular recordings were made in the primary visual cortex. To obtain a representative sample of cortical cells, units were studied at regularly spaced intervals along the course of electrode penetrations traveling oblique to the cortical surface. An automated assessment of preferred orientation using a computer-driven optical display was employed, and during the recording session the experimenters did not know which orientation(s) each animal had viewed in early life. 3. In the cats that viewed horizontal lines with one eye and vertical lines with the other during rearing, two major findings of previous workers (14) were confirmed. First, a majority of units were not selective for orientation. Second, units with preferred orientations near vertical tended to be activated exclusively by the eye that had viewed vertical, and likewise for horizontal. 4. In cats that viewed lines of the same orientation with both eyes during rearing, a substantially smaller proportion of units were selective for orientation; the preferred orientations of these units also tended to match the orientation to which the cats had been exposed. 5. Portions of some electrode penetrations showed an orderly arrangement of cells according to preferred orientation similar to that seen in normal cats, but with regions over which only nonselective cells were found. Many penetrations appeared less orderly. 6. The results are consistent with a role for early visual experience in maintaining the responsiveness and innate selectivity of cortical neurons, although they cannot entirely rule out the possibility that experience may alter or determine the preferred orientation of some cells.

Animals↗
PubMed1988

Temporal sequence of neurotransmitter expression by developing neurons of fetal monkey visual cortex.

The developing fetal monkey visual cortex was studied immunocytochemically from 110-155 days post-conception in order to localize cell populations immunoreactive (ir) for gamma-aminobutyric acid, Substance P, cholecystokinin-octapeptide, somatostatin, neuropeptide Y, and proenkephalin A peptide (BAM-18). The area 17/18 border and all cortical laminae identified in the adult visual cortex were discernible from the youngest age examined. All ir-cell populations studied were present at each fetal age. However, despite a relatively adult-like cytoarchitecture, all ir-cell populations studied displayed patterns of immunostaining which were unlike those described in adult visual cortex, and showed significant changes in laminar distribution, morphology, and numbers over the time course of gestation examined. Despite the differences in the patterns of immunostaining between the fetal and adult visual cortex, ir-cell populations intrinsic to the developing visual cortex exhibited adult-like combinations of co-localized transmitters and peptides. The developing monkey cortex also contains ir-cell populations, particularly BAM-18-ir cells, which have not been detected immunocytochemically in the adult monkey cortex. Differences between the fetal and the adult ir-cell populations might be accounted for by cell death, morphological transformation, secondary migration or changes in gene expression for neurotransmitters and neuropeptides.

Animals↗
PubMed1987

Glucose utilization of visual cortex following extra-occipital interruptions of the visual pathways by tumor. A positron emission tomography study.

To assess the effect of extra-occipital lesions on the local cerebral glucose utilization of the primary and associative visual cortex, 29 patients were studied in the unstimulated state by positron emission tomography and [18F]2-deoxyglucose. Quantitative Goldmann perimetry was done in each patient at the time of the positron emission tomographic study. Nine patients showed homonymous defects, either hemianopsia or quadrantanopsia, whereas nine patients had heteronymous defects. Eleven control subjects, free of any neurological symptoms and with normal visual fields, were also studied with [18F]2-deoxyglucose positron emission tomography. In the normal control subjects and in patients with a heteronymous defect, left-to-right differences in the local cerebral metabolic rate for glucose of the visual cortex varied less than 10%. In patients with hemianopic defects, differences ranged from 8 to 38%, with the hypometabolic cortex always contralateral to the field defect. In patients with quadrantanopic defects, the visual cortex contralateral to the field defect demonstrated differences from 14 to 24% above and below the calcarine fissure, the cortex that received greater input from the affected field being hypometabolic.

Adult↗
PubMed1989

Horizontal organization of orientation-sensitive cells in primate visual cortex.

In the visual cortex of the monkey the horizontal organization of the preferred orientations of orientation-selective cells follows two opposing rules: (1) neighbors tend to have similar orientation preferences, and (2) many different orientations are observed in a local region. We have described a classification for orientation maps based on the types of topological singularities and the spacing of these singularities relative to the cytochrome oxidase blobs. Using the orientation drift rate as a measure we have compared simulated orientation maps to published records of horizontal electrode recordings.

Animals↗
PubMed1989

Orientation discrimination sensitivity of single units in cat primary visual cortex.

Responses of visual cortex (area 17) neurons to moving oriented stimuli were recorded from anesthetized cats. The variance of response (SD2) to repeated identical stimuli was directly proportional to response magnitude (R), (SD2 = C2R). The values of C were not found to differ significantly between different types of cortical cells. The relationship predicts that the coefficient of variation (SD/R) will be smallest near the peak of the tuning curve, indicating that the peak response is most reliable for detecting an orientation but not necessarily the most sensitive to a change in orientation. Tuning curves and response variability were then examined to determine the orientation at which the neuron was most sensitive to changes in stimulus orientation using signal detection theory. The discrimination index (d' = [R1-R2]/SD) for a 1 degree change in stimulus orientation was greatest along the flanks of the tuning curve. In order to generalize the experimental data, response distributions derived from a model of cells with parameters based on experimental data were examined to determine the minimal discriminable change in stimulus orientation. Changes of stimulus orientation between 0.6 and 5 deg of arc could be detected from single responses of a single cell by an optimal observer with 75% accuracy if the orientation change was centered at the most sensitive part of the tuning curve.

Action Potentials↗
PubMedDate not supplied

A comparison of inhibition in orientation and spatial frequency selectivity of cat visual cortex.

Neurones in the visual cortex are highly selective for orientation and spatial frequency of visual stimuli. There is strong neurophysiological evidence that orientation selectivity is enhanced by inhibitory interconnections between columns in the cortex which have different orientation sensitivities, an idea which is supported by experiments using neuropharmacological manipulation or complex visual stimuli. It has also been proposed that selectivity for spatial frequency is mediated in part by a similar mechanism to that for orientation, although evidence for this is based on special use of visual stimuli, which hampers interpretation of the findings. We have therefore examined selectivity for both orientation and spatial frequency using a technique which allows direct inferences about inhibitory processes. Our method uses microiontophoresis of an excitatory amino acid to elevate maintained discharge of single neurones in the visual cortex. We then present visual stimuli both within and outside the range of orientations and spatial frequencies which cause a cell to respond with increased discharge. Our results show that orientations presented on either side of the responsive range usually produce clear suppression of maintained discharge. In marked contrast, spatial frequencies shown to either side of the responsive range have little or no effect on maintained activity. We conclude that there is an intracortical organization of inhibitory connections between cells tuned to different orientations but not different spatial frequencies.

Animals↗
PubMed1991

Calcium binding proteins and neuropeptides as molecular markers of GABAergic interneurons in the cat visual cortex.

In the cat visual cortex, almost all parvalbumin-positive cells are GABAergic, and about 80% of the calbindin D-28K-positive neurons are also GABA-immunoreactive. About 37% of the GABAergic neurons contain parvalbumin and a smaller fraction (about 18%) contains calbindin. Furthermore, parvalbumin and calbindin are localized in two separate neuronal populations in the cat visual cortex, suggesting that two GABAergic populations can be distinguished, one containing parvalbumin and one containing calbindin. Double staining for parvalbumin and neuropeptides (CCK, SRIF and NPY), revealed no double-labeled cells, with the exception of a few SRIF- and parvalbumin-positive neurons. These results show that cortical GABAergic cells can be differentiated on basis of their calcium binding protein and neuropeptide immunoreactivity.

Animals↗