Displaced amacrine cells in the ganglion cell layer of the ground squirrel retina

In some mammals a large portion of the retinal neurons of the ganglion cell layer are not ganglion cells. These neurons, lacking axons which pass to the brain via the optic nerve, are termed displaced amacrine cells. The present study assessed the number of displaced amacrine cells in the thirteen-lined ground squirrel (Spermophilus tridecemlineatus). We compared the number of labeled cells in the ganglion cell layer after HRP injection of optic tracts and target nuclei with the total number of neurons in the ganglion cell layer. We conclude that approximately one half of the neurons in the ganglion cell layer are displaced amacrine cells, the other one half are ganglion cells. The displaced amacrine cells are on the average smaller than the ganglion cells. Our results provide a rationale for renewed study of relation of ganglion cell morphology and physiological functional type in this species.