EXPRESSION AND DOWN-REGULATION OF THE GABAERGIC PHENOTYPE IN EXPLANTSOF CULTURED RABBIT RETINA

Purpose. To study the morphologic and neurochemical development of the rabbit retina in explant culture. Methods. Explants of retina from ne wborn rabbits were cultured in defined medium in the absence of serum or soluble growth factors. The morphology of the explant and the neuro -chemical development of the GABAergic system were examined by light m icroscopy, autoradiography, and immunohistochemistry for 7 days and co mpared to those of the postnatal rabbit retina on vivo. Results. Cultu red explants from newborn rabbit retina develop and maintain well-defi ned plexiform and cellular layers up to 7 days. Exogenous H-3-gamma-am inobutyric acid (GABA) and antibodies against GABA labeled a populatio n of horizontal, amacrine, and displaced amacrine cells in the ganglio n cell layer during the first 3 days in culture. After 4 days in cultu re, the extent of uptake and immunolabeling was diminished among all t hree cell types, but labeled horizontal cells were markedly rare. At 7 days in culture, uptake and GABA-like immunoreactivity could not be d etected in horizontal cells, but antibodies to calbindin-D reacted wit h horizontal and amacrine cells in the appropriate retinal layers. Pea nut agglutinin lectin binding studies revealed a mosaic of cone photor eceptor inner segments indistinguishable from that of neonatal retina in vivo. Conclusions. The experiments show that the maturation of cell ular layers and the development expression of the GABAergic phenotype can be observed in retinal explants cultured under chemically defined conditions. Histochemical evidence is presented that indicates culture d explants of newborn rabbit retinas express markers of the GABAergic phenotype in a manner consistent with that observed in vivo. The autho rs show that horizontal cells continue to survive in culture after the diminution in GABA immunoreactivity.