[ 3 H]Spiperone Labels Non‐Cyclase‐Linked Dopamine Receptors in the Ventral Tegmental Area of Rat Brain

The binding of [ 3 H]spiperone, a neuroleptic/dopamine receptor ligand, to membranes of the ventral tegmental area of the rat was studied in vitro and found to be rapid, saturable, reversible, and of high affinity. Specific binding was displaced by the dopaminergic agonists dopamine, apomorphine, and 2‐amino‐6,7‐dihydroxytetralin, and stereospecifically by the neuroleptic drugs butaclamol and flupenthixol. Bromocryptine and other ergots displaced the binding, as did the D‐2 antagonists domperidone, molindone, metoclopramide, and sulpiride. Noradrenergic, histaminergic, and serotonergic components of the binding were not detected in displacement studies with various agonists and antagonists. These data are consistent with the hypothesis that [ 3 H]spiperone labels dopamine receptors in the ventral tegmental area that are not linked to adenylate cyclase and are therefore likely to be of the D‐2 type.