RETINOID EFFECTS IN PURIFIED CULTURES OF CHICK-EMBRYO RETINA NEURONS AND PHOTORECEPTORS

Purpose. To investigate the effects of retinoic acid, retinol, and 11- cis retinaldehyde on proliferation, differentiation, and survival of c ultured embryonic chick neural retina cells; to describe the metabolic transformations of these retinoids by the cultured cells. Methods. Re tinoids were added to glia-free, low-density cultures of neural retina cells, which underwent subsequent examination to determine the number s of neurons and photoreceptors that differentiated and survived under differing conditions. Cells and conditioned medium were extracted to identify and quantify retinoid metabolic products by high pressure liq uid chromatography. Results. Retinoid treatment resulted in dose-depen dent increases in the number of differentiated photoreceptors present in the cultures after 6 days; smaller increases in nonphotoreceptor ne urons were also observed. Retinoids were more effective when added at culture onset than at later times, but they did not stimulate cell pro liferation. The order of potency was retinol > 11-cis retinaldehyde > retinoic acid. Exogenous retinoic acid was recovered unmodified after a 24-hr incubation period; retinol was also stable and unmetabolized, except for the formation of a small quantity of retinyl acetate. 11-ci s retinaldehyde was less stable, and was metabolized into both retinoi c acid and retinol. Conclusions. Retinol, 11-cis retinaldehyde, and re tinoic acid can promote the survival (and possibly differentiation) of cultured embryonic retina neurons and photoreceptors in the absence o f glia and retinal pigment epithelium. Although retinoic acid is likel y to function by interacting with one of the known nuclear receptors f or this retinoid, the effectiveness of retinol in the absence of metab olic transformation into retinoic acid suggests the possible existence of a distinct, yet undiscovered receptor.