Number of neurons in the retinal ganglion cell layer of the quokka wallabydo not change throughout life

During adult life, the topography of the retinal pigment epithelium (RPE) o f the quokka wallaby changes gradually. Cells in peripheral retina enlarge in surface area while those in mid-temporal retina, adjacent to the area ce ntralis, a high density region in the ganglion cell layer, decrease in area , implying that the tissue in this area is drawing together. We speculated that high ganglion cell densities in temporal regions might be maintained, in the face of cell loss due to aging, by this apparent drawing together of the RPE sheet. Therefore, we examined the retinal ganglion cell layer of t he quokka in cresyl violet stained wholemounts from animals aged from 0.55 to 13.5 years. We found that total neuron number in the retinal ganglion ce ll layer of the quokka did not decrease significantly throughout life even though individuals in captivity live long lives (9-15 years). Ganglion and amacrine cells were counted separately and identified by strict morphologic al criteria. Nevertheless, the proportion of ganglion to amacrine cells app eared to decrease linearly throughout life, indicating that the morphology of a proportion of neurons became more amacrine-like during aging. Mean cel l size did not change throughout life. In the quokka, retinal area increase s slowly throughout life and may account for the small reduction in cell de nsity seen in most retinal regions. Anat Rec 256:78-83, 1999. (C) 1999 Wile y-Liss, Inc.