The projection of different retinal ganglion cell classes to the dorsal lateral geniculate nucleus in the hooded rat.

The morphology of retinal ganglion cells which project to different parts of the dorsal lateral geniculate nucleus (DLG) in the hooded rat has been investigated. Small amounts of a retrograde tracer (horseradish peroxidase) were injected into the DLG, then labelled retinal ganglion cells were examined in retinal wholemounts. After injections into different parts of the DLG, differences were noted in the size, morphology and retinal distribution of labelled retinal ganglion cells. Specifically, after injections into the antero-ventral part of the DLG labelled retinal ganglion cells were spread sparsely across the retina, had large cell somas, and many were identified with Class I or Class III morphology. After injections into the postero-dorsal part of the DLG, labelled cells were more densely packed, had smaller somas, and more were identified with Class IIa and Class III morphology. The density of labelled cells was estimated to be no more than 37% of the total retinal ganglion cell density at any retinal position examined. These results show that in the rat, as in other species such as the cat or monkey, the terminals of different classes of retinal ganglion cells are segregated within different subdivisions of the DLG. However, unlike these other species, only a minority of the total retinal ganglion cell population projects to the DLG.