Increased cell number in the adult hamster retinal ganglion cell layer after early removal of one eye

In hamster, following removal of one eye on the day of birth the amount of normally occurring degeneration in the retinal ganglion cell layer of the remaining eye is reduced, particularly in the temporal retina. To examine the changes in the number and distribution of cells indicated by the alterations in early cell degeneration, adult retinas from hamsters who had one eye removed at birth were compared to those of normal adults. Normal adult retinal ganglion cell layers were found to contain an average of 157,223 cells (a population which includes retinal ganglion cells, "displaced" amacrine cells, and glia). At adulthood, the remaining retinas of early enucleates had an average of 169,863 cells in the ganglion cell layer, an increase of 8%. If only cells having Nissl substance and a soma diameter in excess of 10 micron (a group likely to consist entirely of retinal ganglion cells) are considered, the increase observed was 19%. Cells having Nissl substance and soma diameters between 5 and 10 micron, a group which includes both retinal ganglion cells and displaced amacrines, show a 13% change. Cells less than 10 micron with no Nissl substance visible, which include displaced amacrines and glial cells showed no net change (75,883 versus 75,409). The increase in cell number was found across the entire retina, but was largest in the temporal retina. These results show that alteration in early neuronal survival is a component of early plastic changes in the central nervous system, and that early cell degeneration rates are good predictors of later cell number and distribution.