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PubMedDate not supplied

[Effect of early locomotor training on evoked potentials and the structural organization of the visual cortex dendrites of rats in ontogeny].

Obtained data witness to the fact that increased proprioceptive afferentation influenced by rat running in tretbun during 3-6 months beginning from 1 month age arouses statistically true decrease of latencies, as well as excitation reduction cycles of initial responses of visual cortex on light-flash pairings. Increase of functional activity is registrated better on indices of excitation-reduction cycles, than on latencies of initial responses. Functional reorganization of rat visual cortex correlates with density changes of impregnated dendritic spines. It has been morphologically established that already 3 month-motor training results in statistically true density increase of dendritic spines on neurons of layers II+III and layer V complex. This can be interpreted as indication of increase of afferent flow to neurons of superior and inferior layers of visual cortex.

Aging↗
PubMedDate not supplied

[Laminar analysis of evoked potentials of the cat visual cortex during prenatal ontogenesis].

A laminar analysis of visual evoked potentials recorded from the cortical striate zone in response to stimulation of the optic nerve was made on the cats foeti in the second half of antenatal development and on kittens in the first few days of their life. In all the investigated terms of prenatal ontogenesis, two negativity foci are distinctly revealed in the specific zones of the visual cortex. The first appears with the least latency in the middle cortical layers after an afferent volley inflow to the cortex. The second, which reaches a maximum in 40 to 50 msec appears in the superficial cortical structures. Analysis of the data obtained shows that the first excitation focus is due to the summation of EPSP in the neural elements of the middle cortical layers, while the second is caused by development of depolarization in the apical dendrites of the pyramidal neurones.

Animals↗
PubMed1997

Distortions of visuotopic map match orientation singularities in primary visual cortex.

The map of orientation columns in primary visual cortex (V1) is known to show strong local distortions, with a generally smooth progression of orientation preference across extended regions of cortex, interrupted by sharp jumps (fractures) and point singularities. The map of visual space on V1, in contrast, has been assumed to be locally smooth and isotropic. We find, on the contrary, that the map of visual space on cat V1 shows strong and systematic local distortions in register with inhomogeneities in the orientation map, with the rate of receptive field movement across cortex being largely proportional to the local rate of change of orientation. This suggests possible systematic local variations in the functional connectivity of short-range lateral connections that underlie local cortical processing.

Animals↗
PubMed1984

Postnatal development of laminar innervation patterns by monoaminergic fibers in monkey (Macaca fascicularis) primary visual cortex.

Immunohistochemical methods are used to characterize the distribution of noradrenergic and serotonergic fibers in primary visual cortex of cynomolgus monkeys (Macaca fascicularis) at various postnatal ages. Previous studies in adult squirrel monkeys have shown that serotonergic fibers are generally restricted to the upper four cortical laminae and are especially dense in layer IV, whereas noradrenergic fibers are especially dense in layers V and VI, moderate in layers I, II, and III, and virtually absent in layer IV (Morrison, J. H., S. L. Foote, M. E. Molliver, F. E. Bloom, and H. G. W. Lidov (1982) Proc. Natl. Acad. Sci. U.S.A. 2401-2405; Morrison, J. H., S. L. Foote, D. O'Connor, and F. E. Bloom (1982) Brain Res. Bull. 9: 309-319). Since these monoamines, especially norepinephrine, have been hypothesized to play an essential role in the developmental plasticity of visual cortex organization (e.g., Kasamatsu, T., and J. D. Pettigrew (1976) Science 194: 206-209; Pettigrew, J. D., and T. Kasamatsu (1978) Nature 271: 761-763), the present study examined the postnatal development of these innervation patterns, especially just before and just after the reported "critical period" for visual plasticity. A dense serotonergic innervation of layer IV is present at birth along with sparse innervation of other laminae. The adult pattern of serotonergic innervation, which is similar to that in the squirrel monkey but even more specifically laminated, becomes evident by 6 weeks of age. In the adult pattern, the most dense innervation remains in layers IVb and IVc. A much lower density of noradrenergic than of serotonergic fibers is evident at all ages examined. As with serotonin, the lowest density of fibers is observed at birth. By about 2 months of age these noradrenergic fibers have become more dense, and their laminar distribution is similar to that of adult cynomolgus which is similar to adult squirrel monkey. These studies indicate that: (1) both types of innervation display a continuum of development, with no abrupt changes, (2) serotonergic innervation is more dense than noradrenergic innervation at every age examined, (3) these two transmitter systems exhibit very different laminar innervation patterns as early as birth, and (4) the greater laminar specialization of area 17 in cynomolgus versus squirrel monkeys is accompanied by corresponding enhanced laminar specialization of these monoaminergic afferents.

Aging↗
PubMed1982

Types of synapses contacting the soma of corticotectal cells in the visual cortex of the cat.

Retrograde transport of horseradish peroxidase has been used to single out a distinct functional cortical cell type for ultrastructural study. Following injection of horseradish peroxidase into the superior colliculus, labelled pyramidal cells were found in layer V of the visual cortex. Examination of the labelled corticotectal cells from the visual cortex showed that their cell bodies received two types of synaptic contacts, one from boutons containing spherical vesicles and one from boutons containing flattened vesicles. The possible functional significance of this dual type of input is pointed out.

Animals↗
PubMed2004

Adaptive temporal integration of motion in direction-selective neurons in macaque visual cortex.

Direction-selective neurons in the primary visual cortex (V1) and the extrastriate motion area MT/V5 constitute a critical channel that links early cortical mechanisms of spatiotemporal integration to downstream signals that underlie motion perception. We studied how temporal integration in direction-selective cells depends on speed, spatial frequency (SF), and contrast using randomly moving sinusoidal gratings and spike-triggered average (STA) analysis. The window of temporal integration revealed by the STAs varied substantially with stimulus parameters, extending farther back in time for slow motion, high SF, and low contrast. At low speeds and high SF, STA peaks were larger, indicating that a single spike often conveyed more information about the stimulus under conditions in which the mean firing rate was very low. The observed trends were similar in V1 and MT and offer a physiological correlate for a large body of psychophysical data on temporal integration. We applied the same visual stimuli to a model of motion detection based on oriented linear filters (a motion energy model) that incorporated an integrate-and-fire mechanism and found that it did not account for the neuronal data. Our results show that cortical motion processing in V1 and in MT is highly nonlinear and stimulus dependent. They cast considerable doubt on the ability of simple oriented filter models to account for the output of direction-selective neurons in a general manner. Finally, they suggest that spike rate tuning functions may miss important aspects of the neural coding of motion for stimulus conditions that evoke low firing rates.

Action Potentials↗
PubMed1999

Enhancement of activity-dependent calcium increase by neurotrophin-4 in visual cortex pyramidal neurons.

In pyramidal neurons from rat visual cortex slices, bath-application of NT-4 (20 ng/ml) did not much affected the baseline calcium signal, but did enhance calcium signals elicited by injections of depolarizing currents (+0.5 nA, 1 s). This enhancing effect of NT-4 was abolished by co-applying K252a. With ryanodine injected intracellularly, the effect of NT-4 was significantly reduced, suggesting an involvement of intracellular calcium release in this NT-4-induced enhancement of calcium transient.

Animals↗
PubMed2002

A novel mechanism of response selectivity of neurons in cat visual cortex.

The spiking of cortical neurons critically depends on properties of the afferent stimuli. In the visual cortex, neurons respond selectively to the orientation and direction of movement of an object. The orientation and direction selectivity is improved upon transformation of the membrane potential changes into trains of action potentials. To address the question of whether the transformation of the membrane potential changes into spiking of a cell depends on the stimulus orientation and the direction of movement, we made intracellular recordings from the cat visual cortex in vivo during presentation of moving gratings of different orientations. We found that the relationship between the membrane polarization and the firing rate (input-output transfer function) depended on the stimulus orientation. The input-output transfer function was steepest during responses to the optimal stimulus; membrane depolarization of a given amplitude led to generation of more action potentials when evoked by an optimal stimulus than during non-optimal stimulation. The threshold for the action potential generation did not depend on stimulus orientation, and thus could not account for the observed difference in the transfer function. Oscillations of the membrane potential in the gamma-frequency range (25-70 Hz) were most pronounced during optimal stimulation and their strength changed in parallel with the changes in the transfer function, suggesting a possible relationship between the two parameters. We suggest that the improved input-output relationship of neurons during optimal stimulation represents a novel mechanism that may contribute to the final sharp orientation selectivity of spike responses in the cortical cells.

Action Potentials↗
PubMed1993

Transient association of the HNK-1 epitope with 5'-nucleotidase during development of the cat visual cortex.

During early postnatal development of the kitten visual cortex the ectoenzyme 5'-nucleotidase undergoes a characteristic redistribution. Until about postnatal week 6 it is essentially confined to synaptic contacts in input layer IV and its expression is related to the use-dependent segregation of thalamic afferents into ocular dominance columns. Subsequently, 5'-nucleotidase becomes distributed uniformly throughout all layers and is then associated selectively with glial cells. Here we describe an age-dependent alteration in the expression of a carbohydrate epitope of 5'-nucleotidase which correlates with the developmental change of the enzyme's localization. We have isolated 5'-nucleotidase from the occipital cortex of kittens of varying age and from adult cats and investigated by immunoblotting the association of the HNK-1 carbohydrate epitope with the protein. 5'-Nucleotidase carries the HNK-1 epitope in kittens of 3-9 weeks but the epitope is absent from 12-week-old kittens or adult cats. Thus, the appearance of the HNK-1 epitope correlates with the transient localization of the enzyme at synapses. The HNK-1 carrying 5'-nucleotidase may be involved in synaptogenesis and use-dependent modifications of synaptic connections.

5'-Nucleotidase↗
PubMed2000

Statistics of lateral geniculate nucleus (LGN) activity determine the segregation of ON/OFF subfields for simple cells in visual cortex.

The receptive fields for simple cells in visual cortex show a strong preference for edges of a particular orientation and display adjacent excitatory and inhibitory subfields. These subfields are projections from ON-center and OFF-center lateral geniculate nucleus cells, respectively. Here we present a single-cell model using ON and OFF channels, a natural scene environment, and synaptic modification according to the Bienenstock, Cooper, and Munro (BCM) theory. Our results indicate that lateral geniculate nucleus cells must act predominantly in the linear region around the level of spontaneous activity, to lead to the observed segregation of ON/OFF subfields.

Animals↗
PubMed2001

Orientation preference patterns in mammalian visual cortex: a wire length minimization approach.

In the visual cortex of many mammals, orientation preference changes smoothly along the cortical surface, with the exception of singularities such as pinwheels and fractures. The reason for the existence of these singularities has remained elusive, suggesting that they are developmental artifacts. We show that singularities reduce the length of intracortical neuronal connections for some connection rules. Therefore, pinwheels and fractures could be evolutionary adaptations keeping cortical volume to a minimum. Wire length minimization approach suggests that interspecies differences in orientation preference maps reflect differences in intracortical neuronal circuits, thus leading to experimentally testable predictions. We discuss application of our model to direction preference maps.

Animals↗
PubMed1984

[Sparsely-spined neurons in the rat visual cortex].

Sparsely spined neurons were described in the visual cortex of the rat. A large cell type was found in all laminae, but mainly in L III-L V. The soma is large and the dendrites are vertically oriented. In most cases, the axon originates from the upper main dendrite or the upper soma pole. The axonal arborization is vertical. In the terminal axonal segments the number of boutons is high. A small neuron type could be demonstrated in L IV. The soma is small, and the dendritic field is nearly multipolarly or horizontally oriented. The axon derives from the basal pole or laterally at the soma.

Animals↗
PubMed2004

Effects of binocular form deprivation on the excitatory post-synaptic currents mediated by N-methyl-D-aspartate receptors in rat visual cortex.

PURPOSE: To investigate the effects of binocular form deprivation (BFD) on the excitatory post-synaptic currents (EPSCs) mediated by the N-methyl-D-aspartate (NMDA) receptor (NMDA-EPSCs), and the proportion of NMDA-EPSCs relative to glutamate receptor currents (glutamate-EPSCs) in rat visual cortex. METHODS: Binocular form deprivation was achieved by suturing the eyelids of Wistar rats at postnatal day (PD) 14, before eye-opening. Visual cortical slices (300 micro m) were prepared from normal and BFD Wistar rats aged PD 14, 21 and 28. Recordings were obtained in slices from layer II to IV using the whole-cell patch-clamp technique. Glutamate-EPSCs were isolated in the presence of bicuculline methiodide (20 micro mol/L) in the bathing medium, and NMDA-EPSCs were isolated with a combination of bicuculline methiodide (20 micro mol/L) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 20 micro mol/L). In addition, D,L-2-amino-5-phosphonovalerate (AP-5, 20 micro mol/L) was applied to study the NMDA-only mediated currents. For each cell, the ratio of peak NMDA to glutamate EPSCs was calculated. RESULTS: During visual development, the decay time constant of NMDA-EPSCs became shorter after eye-opening in normal rats (F = 5.949, P <0.05; PD 28 vs PD 14, P = 0.027), but not in rats with BFD (P > 0.05). The weighted time constant of NMDA-EPSCs in the visual cortex became shorter after the rats' eyes were opened in the normal group (F(2,37) = 4.727, P = 0.015; PD 28 vs PD 14, P = 0.035), but not in the BFD group (P > 0.05). However, the rise time constant and peak value of NMDA-EPSCs showed no significant changes in normal and BFD groups (P > 0.05). The ratio of NMDA-EPSCs to glutamate-EPSCs became gradually smaller with age in the normal rats (F = 4.661, P < 0.05; PD 28 vs PD 14, P = 0.025), but not in the BFD group (P > 0.05). CONCLUSIONS: These studies reveal that the proportion of NMDA-EPSCs relative to glutamate-EPSCs and the decay time constant of NMDA-EPSCs are influenced by BFD. These changes may reflect important experience-dependent modifications of neuronal synapses in visual cortex.

Animals↗
PubMed2005

Effects of long-term potentiation in the human visual cortex: a functional magnetic resonance imaging study.

Applying functional magnetic resonance imaging techniques, hemodynamic responses elicited by slowly flashing checkerboards (0.25 Hz) were measured both before and after a block of rapidly presented checkerboards (9 Hz -- a 'photic tetanus') was delivered. It has been shown previously, using electroencephalography, that this photic tetanus potentiates components of the visual-evoked potential. In the present study, hemodynamic responses in the extrastriate visual cortex were significantly increased to checkerboards presented at a low frequency after the administration of the photic tetanus. These results support the idea that long-term potentiation can be demonstrated non-invasively within the human visual cortex and provide evidence that the plastic changes are localized within the secondary visual cortex.

Brain Mapping↗
PubMed1984

Alterations in receptor number, affinity and laminar distribution in cat visual cortex during the critical period.

The number, affinity, and laminar distributions of various receptors in cat visual cortex were examined during postnatal development using homogenate and in vitro autoradiographic techniques. For all receptor populations examined, the total number of receptors (Bmax) increased from relatively low early values to peak values during the first three months of postnatal life followed by a drop or plateau in the number of receptors. This peak in Bmax occurred during the physiologically-defined period for cortical plasticity. For most receptors examined, the affinity (KD) was also altered during postnatal development. Many of the receptor populations examined exhibited changes in their initial laminar distributions during the first three months of postnatal development, although other did not. The results show a more complex picture of receptor ontogenesis than previously reported, and suggest that the observed receptor modifications affect the synaptic efficacy and the basic chemical circuitry of the visual cortex during the critical period.

Animals↗
PubMed1988

Factors governing the adaptation of cells in area-17 of the cat visual cortex.

Neurons in area 17 of the cat visual cortex adapt when stimulated by drifting patterns of optimal orientation, spatial frequency and temporal frequency (Ohzawa et al. 1982; Albrecht et al. 1984; Ohzawa et al. 1985). A component of this adaptation has been attributed to a contrast gain-control mechanism, rather than to neural fatigue, and results in enhanced differential sensitivity around the adapting contrast level (Ohzawa et al. 1982; Albrecht et al. 1984; Ohzawa et al. 1985). Experiments described here suggest that neural response rate, the directional selectivity of the cell, and the temporal frequency of the stimulus, are the principal determinants of adaptation, irrespective of other stimulus parameters such as contrast, velocity, or spatial frequency. The present results can nevertheless accommodate the results of previous studies of adaptation, and additionally provide scope for the resolution of apparent contradictions between results from psychophysical and neurophysiological studies of adaptation.

Adaptation, Physiological↗
PubMed1994

Partial colocalization of the GABAA receptor with parvalbumin and calbindin D-28K in neurons of the visual cortex and the dorsal lateral geniculate nucleus of the cat.

Monoclonal antibodies to a synthetic peptide fragment of the beta 1-subunit of the bovine central GABAA/benzodiazepine receptor were used to investigate immunocytochemically the distribution of this receptor in the visual system of the cat. Labeled neurons were observed in all layers of the visual cortex and the dorsal lateral geniculate nucleus. About half of the total cortical or geniculate neuronal population was found to be positive. To further identify immunocytochemically these GABAA receptor expressing cells, double stainings were undertaken with, on one hand, the monoclonal antibodies directed against the receptor complex, and on the other hand polyclonal antisera directed against cat muscle parvalbumin or chicken calbindin D-28K. A high degree of colocalization between either of the two calcium binding proteins and the GABAA receptor was found in the upper layers (I, II and III) of the visual cortex and in the A and C laminae of the dorsal lateral geniculate nucleus; all calbindin D-28K-positive cells were immunoreactive for the GABAA receptor. The parvalbumin-positive cells, scattered throughout all layers of the dorsal lateral geniculate nucleus and the visual cortex, except cortical layer I, were also all positive for the GABAA receptor. However, a large proportion of all GABAA receptor bearing cells were negative for one of the calcium binding proteins.

Animals↗
PubMed1999

Perfluorocarbon emulsion improves oxygenation of the cat primary visual cortex.

Tissue PO2 was measured in the primary visual cortex of anesthetized, artificially ventilated, normovolemic cats to evaluate the effect of small doses [1 g perfluorocarbon (PFC)/kg] of a PFC emulsion (1 g PFC/1.1 ml emulsion; Alliance Pharmaceutical, San Diego, CA) on brain oxygenation. The change in tissue PO2 (DeltaPO2), resulting from briefly changing the respiratory gas from room air to 100% oxygen, was measured before and after intravenous infusion of the emulsion. Before emulsion, DeltaPO2 was 51.1 +/- 45.6 Torr (n = 8 cats). Increases in DeltaPO2 of 34.0 +/- 26.1 (SD) % (n = 8) and 16. 3 +/- 8.4% (n = 6) were observed after the first and second emulsion infusions, respectively. The further increase in DeltaPO2 after the third dose (7.9 +/- 10.5%; n = 7) was not statistically significant. The observed increases in tissue oxygenation as a result of the PFC infusions appear to be the result of enhanced oxygen transport to the tissue.

Anesthesia↗