DO RETINAL GANGLION-CELLS PROJECT BILATERALLY IN-GROUND SQUIRRELS

Bilaterally projecting retinal ganglion cells have recently been repor ted in the Japanese monkey Macaca fuscata and albino rat. In the prese nt experiments, we sought to determine whether ganglion cells project bilaterally in the 13-lined ground squirrel Spermophilus tridecemlinea tus. We injected rhodamine-conjugated latex microspheres (red beads) i nto the right optic tract, superior colliculus and the dorsal lateral geniculate nucleus and FITC-conjugated latex microspheres (green beads ) into these structures on the left side. In retinal wholemounts of al l subjects, we found cells filled with red beads throughout the left r etina and cells with green beads throughout the right retina. Ipsilate rally projecting ganglion cells were confined to the temporal retina w here they were mixed with cells projecting contralaterally. In no case did we observe a doubly labeled cell. We interpret these observations as indicating that ganglion cells in this species do not project bila terally.