Regional specialization of ganglion cell layer of the chick retina

Specialization of the ganglion cell layer (GCL) was studied by Nissl-strain ing and axonal tract-tracing methods in chicks and chick embryos. The chang es in the retinal area and the cell number in the GCL produced a disparity in the cell density that occurred through the two different processes, cell generation (before embryonic days 10-14, E10-14) and cell loss (after E10- 14). One high-density area was found in the retinal fundus on E8 (presumpti ve central area, pCA) and its density decreased toward the peripheral retin a. Another high-density area was found in the dorsal retina on E11 (presump tive dorsal area, pDA). Cell densities of the pCA and the pDA on E11 decrea sed gradually to 25-30% by P1, and after that they further decreased to 40- 60% by P30. The pCA was still identified on P30, but the pDA became very ob scure by this age. In contrast, ganglion cell sizes increased 5-7 times in the pCA and pDA from E8 to P30, and increased 12 times in the temporal peri phery. The present study suggests that the center-peripheral gradient of ce ll density results from lager scale of cell genesis in the pCA, but not fro m lager scale of cell loss in the peripheral retina. However, obscuration o f the pDA results from equalization of cell density in cellular degeneratio n processes.