Do retinal ganglion cells project bilaterally in ground squirrels?

Bilaterally projecting retinal ganglion cells have recently been reported in the Japanese monkey Macaca fuscata and albino rat. In the present experiments, we sought to determine whether ganglion cells project bilaterally in the 13-lined ground squirrel Spermophilus tridecemlineatus. We injected rhodamine-conjugated latex microspheres (red beads) into 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 all subjects, we found cells filled with red beads throughout the left retina and cells with green beads throughout the right retina. Ipsilaterally projecting ganglion cells were confined to the temporal retina where 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 bilaterally.