Multiple trophic influences which act on developing retinal ganglion cells: Studies of retinal transplants

This chapter discusses and identifies molecules present in the pathway of growing retinal axons in the developing brain, which might serve as an adhesive substrate. The chapter focuses on the multiple trophic influences, which act on developing retinal ganglion cells. Transplants of retina placed over the superior colliculus of newborn rats form extensive axonal connections with the primary visual nuclei of the host brain. Significantly, different results are obtained, when retina is transplanted to the visual cortex of newborn rats. Collectively, the results make two important points: first, ganglion cells degenerate if unable to form connections in their proper terminal nuclei, and second, retinal axons whether in cortex or colliculus appear to select a very specific path to grow, based on local environmental cues. Transplantation studies offer evidence that laminin is a substrate for retinal axon growth, and fetal retina transplanted adjacent to the colliculus of adult host rats exhibits very limited axon growth into the host brain. Axons from cortical transplants run rostrally and caudally in rather tight tracts deep in the brainstem; however, it remains for future work to distinguish the substrate molecules followed by each axon population.