Density, soma size, and regional distribution of rabbit retinal ganglion cells

Cell soma area or diameter distributions are generally very skewed and present some unusual problems in characterization and description. In this study of ganglion cell soma size in rabbit retina, our conclusions are based on a statistical method which not only characterizes this particular neuronal population but which also may be of considerable value in other species and other parts of the nervous system. To facilitate comparisons between retinas, we used ganglion cell density as the measure of retinal location. The rabbit retina has a horizontally extended area centralis, the visual streak, which we show to have a uniformly high peak cell density along most of its length. Cell density maps were used to estimate the total number of ganglion cells in the retina; the mean for three retinas was about 406,000 cells, which corresponds well to an earlier count of optic nerve axons (394,000 +/- 20,000; Vaney, D.I., and A. Hughes (1976) J. Comp. Neurol. 170: 241-252). Contrary to other reports, we could not find any large differences in ganglion cell size distributions between the inferior peripheral retina and the visual streak nor could we confirm the report of a large cell area temporalis (Provis, J. M. (1979) J. Comp. Neurol. 185: 121-138). Cell size distributions in the superior and inferior retina were very different, however, and, within the inferior retina, there was a small but systematic change in cell size between the periphery and the visual streak. In general, small and medium size cells were present in nearly constant proportions throughout the inferior retina, while the large ganglion cells showed a small decrease in proportion from the periphery to the visual streak; the decline in large cells was a linear function of cell density. In terms of ganglion cell soma size, there was no sharp distinction between the visual streak and the peripheral retina.