The isolated retina of mammals: A useful preparation for enzymatic-(adenylyl cyclase) and/or binding studies of dopamine receptors.

Rabbit and bovine retinae were used for investigations in vitro related to dopamine receptors. Dose-dependent stimulations of cyclic AMP formation induced by dopamine (or dopamine-like drugs including ADTN and some ergot alkaloid derivatives), which can be blocked by dopamine antagonists (neuroleptics), lithium or d-LSD, were found either in intact retinae or in homogenates. The neuroleptic sulpiride was the only exception since it was devoid of inhibitory effects. Binding studies of retinal dopamine receptors were also achieved with homogenates. By using (3)H-spiroperidol as a ligand, saturability (in the amolar range), stereospecificity (by using butaclamol- or thioxanthene-isomers), tissue linearity, and pH- or temperature-dependence were all demonstrated. Furthermore, displacement curves of (3)H-spiroperidol stereospecifically bound generated by various dopamineand/or catecholamine-related drugs seem to indicate that dopamine receptors are the only monoamine receptors in this tissue and that a coupling possibly exists between binding- and catalytic-sites. These results suggest that by studying both dopamine-sensitive adenylyl cyclase and drug-induced displacement of (3)H-spiroperidol binding the mammalian retina is appropriate to selectively characterize the type of action of various drugs with CNS dopamine receptors.