Patchy distribution of NMDAR1 receptors in developing kitten visual cortex

Purpose: During development there is a progressive elaboration and refinement of the various features that become organized into the columnar systems of the adult visual cortex. The columnar organization of several of these features, in particular the ocular dominance columns, is dependent on experiential activity in conjunction with NMDA-mediated plasticity mechanisms. Recent experiments have found that a variety of anatomical markers are distributed in a patchy fashion early in development. This raises the possibility that the known activity-dependence of ocular dominace column development and the newly described patchy features may be linked via a patchy distribution of NMDA receptors in the developing visual cortex. To examine this possibility we have used immunohistochemical techniques to study the distribution of the NMDAR1 receptor subunit in the developing visual cortex. Methods. The arrangement of the NMDAR1 subunit was visualized (using a monoclonal antibody) in flattened and coronal sections through visual cortex. Laminar, as well as areal, changes in the distribution of NMDAR1 was studied during the initial phase of the critical period in kitten visual development (1-6 weeks of age). Results. At each of the ages examined there are regularly spaced patches of dark NMDAR1ir neurons in the visual cortex. Initially, these patches are in the developing cortical plate, and later in upper layers 2/3 extending into layer 1. Conclusions. During development, neurons expressing the NMDAR1 receptor subunit are distributed in a patchy fashion in the upper layers of the kitten visual cortex. This suggests that NMDA-mediated activity-dependent plasticity does not occur uniformly across the tangential extent of the visual cortex, and raises the possibility that the NMDAR1 patches may be presumptive ocular dominance columns.