Choroid coat extract and ciliary neurotrophic factor strongly promote neurite outgrowth in the embryonic chick retina.

Previous studies have shown that extracts from the target optic tectum stimulate neurite outgrowth from retinal explants. The present study indicates that the choroid coat is an even richer source of retinotrophic activity. We thus studied the effects of recombinant rat ciliary neurotrophic factor (CNTF) on primary cultures of dissociated chick ciliary ganglion neurons and retinal explants for a comparison with choroid coat extract from the E18 chick. For our assays, E9 ciliary neurons were incubated in collagen gels and retinal explants were cultured on collagen gels with the addition of the trophic factors and maintained for two or four days. Survival of ciliary neurons per area as well as maximal neurite length in retinal cultures were determined. Growth responses occurred in a dose-dependent manner both to CNTF and choroid extract. Immunofluorescence examination of cells and developing processes showed 200 kdal neurofilament positivity demonstrating that the cells studied were neurons with neurites. It is concluded that a trophic activity of the choroid as well as the recombinant CNTF stimulate retinal neuron survival and neurite extension. The results suggest that CNTF may have developmental functions in the establishment of the visual pathways.