Biomedical subjects

V D Pegado

Publications and source records attributed to V D Pegado.

3 recordsLinked to original sources

PubMed1998

Patchy distribution of NMDAR1 subunit immunoreactivity in developing visual cortex.

Development of ocular dominance columns is dependent on patterned retinal activity, and yet patterned activity alone cannot explain all aspects of cortical column development. Features intrinsic to the cortex have been proposed to interact with activity to guide the patterning of cortical columns (), and the NMDA receptor, because of its role in experience-dependent plasticity, is an obvious candidate. Using immunohistochemical techniques, we found a transiently patchy distribution of the NMDA receptor 1 (NMDAR1) subunit in kitten visual cortex. Regularly spaced patches of NMDAR1-immunoreactive neurons were found at the top of the cortical plate in the developing visual cortex at 2 weeks of age. At 4-5 weeks of age, the radial extent of the NMDAR1 patches spanned the supragranular layers, and by 12 weeks of age, this nonuniform pattern of NMDAR1 immunostaining was no longer apparent. Monocular visual experience prevented the expression of the NMDAR1 patches, but just 4 d of subsequent binocular visual experience was sufficient to promote expression of the patches. Furthermore, the NMDAR1 patches tended to be associated with the borders of ocular dominance columns. These results suggest that the degree of plasticity associated with NMDA-mediated mechanisms is elevated in local regions across the tangential extent of the visual cortex and that the NMDAR1 patches may participate in sculpting the overall arrangement of visual cortical columns.

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PubMed1996

Non-uniform distribution of the NMDAR1 receptor subunit in kitten visual cortex at the peak of the critical period.

PURPOSE: The development of columnar systems in the visual cortex, in particular ocular dominance columns, is dependent on experiential activity in conjunction with NMDA-mediated plasticity mechanisms. Recent experiments, however, have shown that certain aspects of the columnar organization of the visual cortex, such as the spacing of columns, are not changed by manipulations that affect the pattern of retinal activity. This raises the possibility that features intrinsic to the visual cortex may play a crucial role in the development of cortical columns and that a non-uniform distribution of NMDA receptors in the developing visual cortex could form the link between activity and intrinsic cortical modularity. METHODS: To examine this possibility we used immunohistochemical techniques to label the NMDAR1 receptor subunit protein in kitten visual cortex. The arrangement of the NMDAR1 subunit was visualized (using a monoclonal antibody) in flattened and coronal sections through visual cortex. The tangential and laminar distributions of NMDAR1 immunoreactivity (NMDAR1ir) were studied at the peak of the critical period for plasticity (4-5 weeks of age) in the developing kitten visual cortex. RESULTS: At the ages examined there was a non-uniform distribution of NMDAR1 immunoreactivity in the visual cortex. These patches of darker NMDAR1 label were found in layers 2/3 and extended up into layer 1. Thus, during development neurons expressing the NMDAR1 receptor subunit were distributed in a patchy fashion in the upper layers of the kitten visual cortex. CONCLUSIONS: This suggests that NMDA-mediated activity-dependent plasticity may not occur uniformly across the tangential extent of the visual cortex, and raises the possibility that the arrangement of NMDAR1 patches may guide the emergence of nascent columns in the developing visual cortex.

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PubMedDate not supplied

Spacing of cytochrome oxidase blobs in visual cortex of normal and strabismic monkeys.

Some models of visual cortical development are based on the assumption that the tangential organization of V1 is not determined prior to visual experience. In these models, correlated binocular activity is a key element in the formation of visual cortical columns, and when the degree of interocular correlation is reduced the models predict an increase in column spacing. To examine this prediction we measured the spacing of columns, as defined by cytochrome oxidase (CO) blobs, in the visual cortex of monkeys whose binocular vision was either normal or disrupted by a strabismus. The spatial distribution of blobs was examined in seven normal and five strabismic macaques. Tangential sections through the upper layers of the visual cortex were stained to reveal the two-dimensional (2D) pattern of CO blobs. Each blob was localized and their center-to-center spacing, packing arrangement and density were calculated using 2D nearest-neighbor spatial analyses. The mean center-to-center spacing of blobs (590 microm for normally reared and 598 microm for strabismic macaques) and the mean density of blobs (3.67 blobs/mm2 for normally reared and 3.45 blobs/mm2 for strabismic macaques) were not significantly different. In addition, the 2D packing arrangement of the blobs was not affected by strabismus. While it is clear that neural activity plays a key role in the elaboration and refinement of ocular dominance cortical modules, we conclude that it does not determine the spatial period of the pattern of CO blobs. This suggests that aspects of the neural circuitry underlying the columnar architecture of the visual cortex are established prenatally and its fundamental periodicity is not modifiable by experience.

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