Massive retinotectal projection in rats.

Retinal ganglion cells were labeled with horseradish peroxidase injected into the superior colliculus of normal pigmented rats. It is shown that virtually all ganglion cells with crossed axons project to the tectum, thus including all cell types described so far in the rat. The results contrast with the conclusion that only one-third of the ganglion cell population project to the tectum in normal hamsters.