CHOROID COAT EXTRACT AND CILIARY NEUROTROPHIC FACTOR STRONGLY PROMOTENEURITE 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 retinotrop hic activity. We thus studied the effects of recombinant rat ciliary n eurotrophic factor (CNTF) on primary cultures of dissociated chick cil iary ganglion neurons and retinal explants for a comparison with choro id 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 re sponses occurred in a dose-dependent manner both to CNTF and choroid e xtract. Immunofluorescence examination of cells and developing process es showed 200 kdal neurofilament positivity demonstrating that the cel ls studied were neurons with neurites. It is concluded that a trophic activity of the choroid as well as the recombinant CNTF stimulate reti nal neuron survival and neurite extension. The results suggest that CN TF may have developmental functions in the establishment of the visual pathways.