Expression and downregulation of the GABAergic phenotype in explants of cultured rabbit retina.

PURPOSE To study the morphologic and neurochemical development of the rabbit retina in explant culture. METHODS Explants of retina from newborn rabbits were cultured in defined medium in the absence of serum or soluble growth factors. The morphology of the explant and the neurochemical development of the GABAergic system were examined by light microscopy, autoradiography, and immunohistochemistry for 7 days and compared to those of the postnatal rabbit retina in vivo. RESULTS Cultured explants from newborn rabbit retina develop and maintain well-defined plexiform and cellular layers up to 7 days. Exogenous 3H-gamma-aminobutyric acid (GABA) and antibodies against GABA labeled a population of horizontal, amacrine and displaced amacrine cells in the ganglion cell layer during the first 3 days in culture. After 4 days in culture, the extent of uptake and immunolabeling was diminished among all three cell types, but labeled horizontal cells were markedly rare. At 7 days in culture, uptake and GABA-like immunoreactivity could not be detected in horizontal cells, but antibodies to calbindin-D reacted with horizontal and amacrine cells in the appropriate retinal layers. Peanut agglutinin lectin binding studies revealed a mosaic of cone photoreceptor inner segments indistinguishable from that of neonatal retina in vivo. CONCLUSIONS The experiments show that the maturation of cellular layers and the developmental expression of the GABAergic phenotype can be observed in retinal explants cultured under chemically defined conditions. Histochemical evidence is presented that indicates cultured explants of newborn rabbit retinas express markers of the GABAergic phenotype in a manner consistent with that observed in vivo. The authors show that horizontal cells continue to survive in culture after the diminution in GABA immunoreactivity.