A quantitative comparison between the ganglion cell populations and axonal outflows of the visual streak and periphery of the rabbit retina

Abstract

A vertical density profile of the ganglion cells 2 mm temporal of the optic nerve head in the rabbit retina has been produced by counting somata in the cresyl-violet-stained, ganglion cell layer of a flat-mounted retina. Somata classified as ganglion cells were characterized by obvious Nissl staining in an extensive cytoplasm and typically had diameters greater than 9 micrometer. The accuracy of the profile, and thus of the classification criteria, has been substantiated by electron micrographic determination of the numbers of ganglion cell axons arising within local regions of known area on the same retina. This study indicates that Vaney and Hughes' estimate ('76) of 547,100 presumed ganglion cells in the rabbit retina should be changed to 373,500 ganglion cells. The latter value is within the statistical error of their optic nerve count of 394,000 fibers. The mean diameter of ganglion cells 6 mm from the visual streak in the inferior periphery (density: 550 cells/mm2) was 28% greater than that of cells on the peak of the streak (density: 5,400 cells/mm2), although the form of the ganglion cell diameter distribution did not change markedly with eccentricity. The increase in the mean size of ganglion cells in the periphery appeared to be approximately matched by an increase in the size of their axons. Larger axons became myelinated farther from the edge of the myelinated band than did smaller axons. Within the ganglion cell layer there was another population of cells which were quite distinct from the obvious neuroglia: Their nuclei were similar to those of the larger ganglion cells and many appeared to have Nissl granules within their limited cytoplasm. About half of this heterogeneous population was classified as "coronate cells," which were characterized by the partial nuclear encapsulation of their eccentric cytoplasm.