RETINAL GANGLION-CELLS IN NORMAL HAMSTERS AND HAMSTERS WITH NOVEL RETINAL PROJECTIONS .1. NUMBER, DISTRIBUTION, AND SIZE

We examined the number, spatial distribution, and size of ganglion cel ls in the retinae of normal Syrian hamsters and hamsters with retinal projections to the auditory and somatosensory nuclei of the thalamus, induced by neonatal surgery. As revealed by retrograde filling with ho rseradish peroxidase, there are about 64,600 contralaterally projectin g retinal ganglion cells (RGCs) and 1,700 ipsilaterally projecting RGC s in the retinae of normal adult hamsters. Contralaterally projecting RGCs are distributed throughout the retina and have two local density peaks located within a central streak of high RGC density that is orie nted approximately along the nasal-temporal axis. RGC density falls ab ove and below the central streak, with a steeper gradient towards the upper retina. Ipsilaterally projecting RGCs are diffusely distributed within a crescent at the inferotemporal retinal periphery and are most dense at the internal border of the crescent. The soma diameter of co ntralaterally projecting RGCs ranges from 6 to 25 mu m; the diameter d istribution is unimodal, with a peak in the 10-13 mu m range and is sk ewed toward smaller values, with an elongated tail towards higher valu es. Contralaterally projecting RGCs tend to be smaller in regions of h igher density. Ipsilaterally projecting RGCs tend to be larger than co ntralaterally projecting RGCs both globally and within the temporal cr escent, and their size distributions tend to be less regular and less well related to local density. The retinae of neonatally operated hams ters with novel retinal projections to the auditory and somatosensory systems contain about one-fourth the normal number of contralaterally projecting RGCs, whose relative density distribution is approximately normal despite the drastic reduction of absolute RGC density. The rang e and distribution of RGC soma diameters are similar in normal and neo natally operated hamsters, and, in operated as in normal hamsters, con tralaterally projecting RGC somata tend to be smaller in regions of hi gher density. Our results in normal hamsters suggest a role for intrar etinal mechanisms in the determination of RGC size. Our findings in ne onatally operated hamsters suggest that, despite the reduced number of RGCs in these animals, the same types of RGCs are found in the retina e of normal and neonatally operated hamsters. (C) 1995 Wiley-Liss, Inc .