Retinal ganglion cell projections to individual layers of the lateral geniculate body in Galago crassicaudatus

Abstract

The genus Galago provides an unique opportunity to study the relation between layers of the lateral geniculate body and classes of retinal ganglion cells. In the present experiments HRP was restricted to individual layers of the lateral geniculate body with the following results: After injections of the magnocellular layers, layers 1 and 2, labeled retinal ganglion cells ranged in size from 8 to 20 micrometers. After injections of the parvocellular layers, layers 3 and 6, labeled retinal ganglion cells ranged in size from 6 to 12 micrometers. After injections involving layers 4 and 5, which layers contain only very small, pale cells, labeled retinal ganglion cells ranged in size from 5 to 14 micrometers. Thus, the very largest ganglion cells were labeled only after injections of magnocellular layers 1 and 2, while small and medium retinal ganglion cells were labeled after HRP injections in every layers of the lateral geniculate body. Because the magnocellular layers actually contain a mixture of large, medium, and small-sized cells, we suggest that retinal ganglion cells of different size-classes project to geniculate relay cells of the corresponding size-class.