LOCALIZATION OF PUTATIVE DOPAMINE D-2-LIKE RECEPTORS IN THE CHICK RETINA, USING IN-SITU HYBRIDIZATION AND IMMUNOCYTOCHEMISTRY

The actions of dopamine are mediated by 5 or more receptor subtypes, a ny of which may be coupled by G-proteins to adenylate cyclase (D-1-fam ily: stimulatory, D-2-family: inhibitory or no action). Postnatal ocul ar growth in the chick is a vision-dependent mechanism which involves D-2-type receptors in either the retina or the retinal pigment epithel ium (RPE). Although the dopaminergic amacrine cells are well described in the chick retina, only D-2-receptors, but not D-3- and D-4-recepto rs have been clearly localized, and the cells that express them have n ot been identified. In this study we showed that immunoreactive D-2/3- receptor protein is localized to the photoreceptor inner segments, out er and inner plexiform layer and ganglion cell layer, as described pre viously (Wagner et al., J. Comp. Neurol., 330 (1993) 1-13). D-2-recept or mRNA was localized to cell bodies in all nuclear layers of the reti na, whereas D-4-receptor mRNA. was restricted to the inner half of the retina. Immunoreactive D-2-type receptors and their mRNA were observe d also in the basal region of the RPE. Because of the widespread distr ibution of both D-2- and D-4-receptor mRNA in the chick retina and RPE and the lack of D-3- and D-4-receptor-specific antibodies, we were un able to identify which of the D-2/3/4-receptor-bearing cells are invol ved in controlling ocular growth.