Changes in inner plexiform layer thickness following neonatal visual cortical ablation in cats.

Abstract

The effect of visual cortex removal at 5-7 days of age on the development of the inner nuclear and inner plexiform layers of the cat's retina was examined in animals which had survived 9-36 months after the cortical removal. The lesions were unilateral so that only the nasal or the temporal region of each retina was affected, and the affected regions were positively identified by HRP injection into the optic tract either ipsilateral or contralateral to the ablated hemisphere. Small sections of retina straddling the naso-temporal boundary were then embedded in plastic and sectioned radially for analysis. In this way, comparisons could be made between areas of retina which were closely matched in terms of location as well as histological history. Cells in the inner nuclear layer in affected regions of retina appeared normal both in number and size, even though ganglion cell density in these areas was clearly reduced. This indicates that, at least at this age, the survival of inner nuclear layer cells does not depend on the availability of ganglion cells as synaptic targets. Paradoxically, in the affected regions of retina there was an increase in the width of the inner plexiform layer which was not associated with any change in the thickness of other, more distal retinal layers. This could be due either to an increased growth of surviving ganglion cells and/or inner nuclear layer cells, or to an increase in the survival of cells in the ganglion cell layer, perhaps displaced amacrine cells, which have a greater dendritic volume than the lost ganglion cells.