A Quantitative Analysis of Cells in the Ganglion Cell Layer of the Chick Retina

Abstract

This study investigated the organization of cells in the ganglion cell layer (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 × 10⁶ (P-1) and 4.9 × 10⁶ (P-8), and the cell density was 14,300 cells/mm² (P-1) and 10,400 cells/ mm² (P-8) on average. Two high-density areas, the central area (CA) and the dorsal area (DA), were observed in the central and dorsal retinas in both P-1 (22,000 cells/mm² in CA, 19,000 cells/mm² in DA) and P-8 chicks (19,000 cells/mm² in CA, 12,800 cells/mm² in DA). The cell densities in the temporal periphery (TP) and the nasal (NP) peripheral retinas were 7,800 cells/mm² and 12,500 cells/mm², respectively, in P-1 and 5,000 cells/ mm² and 8,000 cells/mm², respectively, in P-8 chicks. The cell density in the temporal periphery was 35% (P-8) lower than in the nasal periphery in both P-1 and P-8 chicks. Thirty percent (1.9 × 10⁶ cells in P-1) of the total cells in the GCL were resistant to axotomy of the optic nerve. The distribution of the axotomy-resistant cells showed two high-density areas in the central and dorsal retinas, corresponding to the CA (5,800 cells/mm²) and the DA (3,200 cells/mm²). These cells also exhibited a center-peripheral increase (2,200 cells/mm² in the TP) in P-1 chicks, but the high-density area was not found in the dorsal retina of P-8 chicks. From these data and the HRP study, the number of presumptive ganglion cells in P-8 chicks was estimated to be 4 × 10⁶ (8,600 cells/mm² on average), and the density in each area was 13,500 (CA), 10,200 (DA), and 4,300 (TP) cells/mm². 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 periphery (TP/CA ratio: 0.47 in P-1 and 0.32 in P-8) than toward the nasal periphery (NP/CA ratio: 0.67 in P-1 and 0.52 in P-8). In contrast, there was no significant difference in the peripheral/center ratios between the dorsal retina (DP/CA ratio: 0.6 in P-1 and 0.56 in P-8) and ventral retina (VP/CA ratio: 0.58 in P-1 and 0.51 in P-8). A small peak in the density of the presumptive ganglion cells was detected in the dorsal retina of both P-1 chicks (10,800 cells/mm²) and P-8 chicks (10,200 cells/mm²). The HRP-labeled cells were small in the CA (M ± SD: 35.7 ± 9.1 μm²) and DA (40.0 ± 11.3 μm²), and their sizes increased toward the periphery (63.4 ± 29.7 μm² in the TP) accompanied by a decrease in the cell density. However, the axotomy-resistant cells did not significantly increase in size toward the peripheral retina (12.2 ± 2.2 μm² in the CA, 15.2 ± 3.2 μm² in the DA, 15.1 ± 3.8 μm² in the TP). The characteristic distribution of ganglion cells could be related to visual behavior based upon the specialization of avian visual fields.