A quantitative analysis of cells in the ganglion cell layer of the chick retina

This study investigated the organization of cells in the ganglion cell laye r (GCL) using Nissl staining, retrograde cell degeneration with axotomy of the optic nerve, and retrograde cell labeling by injections of horseradish peroxidase (HRP) into the optic nerve of chicks (posthatching day 1 and 8, P-1 and P-8). The total number of cells in the GCL was 6.1 x 10(6) (P-l) an d 4.9 x 10(6) (P-8), and the cell density was 14,300 cells/mm(2) (P-l) and 10,400 cells/mm(2) (P-8) on average. Two high-density areas, the central ar ea (CA) and the dorsal area (DA), were observed in the central and dorsal r etinas in both P-l (22,000 cells/mm(2) in CA, 19,000 cells/mm(2) in DA) and P-8 chicks (19,000 cells/mm(2) in CA, 12,800 cells/mm(2) in DA). The cell densities in the temporal periphery (TP) and the nasal (NP) peripheral reti nas were 7,800 cells/mm(2) and 12,500 cells/mm(2), respectively, in P-l and 5,000 cells/mm(2) and 8,000 cells/mm(2), respectively, in P-8 chicks. The cell density in the temporal periphery was 35% (P-8) lower than in the nasa l periphery in both P-l and P-8 chicks. Thirty percent (1.9 x 106 cells in P-l) of the total cells in the GCL were resistant to axotomy of the optic n erve. The distribution of the axotomy-resistant cells showed two high-densi ty areas in the central and dorsal retinas, corresponding to the CA (5,800 cells/mm(2)) and the DA (3,200 cells/mm(2)). These cells also exhibited a c enter-peripheral increase (2,200 cells/mm(2) in the TP) in P-l chicks, but the high-density area was not found in the dorsal retina of P-8 chicks. Fro m these data and the HRP study, the number of presumptive ganglion cells in P-8 chicks was estimated to be 4x10(6) (8,600 cells/mm(2) on average), and the density in each area was 13,500 (CA), 10,200 (DA), and 4,300 (TP) cell s/mm(2), The peripheral/center ratios of the density of ganglion cells were significantly different along the nasotemporal and dorsoventral axes. The density of ganglion cells decreased more rapidly toward the temporal periph ery (TP/CA ratio: 0.47 in P-l and 0.32 in P-8) than toward the nasal periph ery (NP/CA ratio: 0.67 in P-l and 0.52 in P-8). In contrast, there was no s ignificant difference in the peripheral/center ratios between the dorsal re tina (DP/CA ratio: 0.6 in P-l and 0.56 in P-8) and ventral retina (VP/CA ra tio: 0.58 in P-l and 0.51 in P-8). A small peak in the density of the presu mptive ganglion cells was detected in the dorsal retina of both P-l chicks (10,800 cells/mm(2)) and P-8 chicks (10,200 cells/mm(2)). The HRP-labeled c ells were small in the CA (M +/- SD: 35.7 +/- 9.1 mu m(2)) and DA (40.0 +/- 11.3 mu m(2)), and their sizes increased toward the periphery (63.4 +/- 29 .7 mu m(2) in the TP) accompanied by a decrease in the cell density. Howeve r, the axotomy-resistant cells did not significantly increase in size towar d the peripheral retina (12.2 +/- 2.2 mu m(2) in the CA, 15.2 +/- 3.2 mu m( 2) in the DA, 15.1 +/- 3.8 mu m(2) in the TP). The characteristic distribut ion of ganglion cells could be related to visual behavior based upon the sp ecialization of avian visual fields.