D1 receptor binding in rat striatum: modification by various D1 and D2 antagonists, but not by sibutramine hydrochloride, antidepressants or treatments which enhance central dopaminergic function.

[3H]SCH 23390 is a selective high affinity ligand for D1 receptors in vitro. Using this ligand persistent blockade of D1 receptors by SCH 23390 and cis-flupenthixol was shown to significantly increase the number of D1 receptor binding sites in rat striatum. In contrast, repeated administration of the D2-selective antagonist, clebopride, resulted in a small, but significant, reduction in number. No differences in binding affinity were observed and a single dose of these compounds was without effect. The D2-selective antagonist, haloperidol, the non-selective D1/D2 receptor antagonist, chlorpromazine, the dopamine reuptake inhibitors, bupropion, GBR 12909 and nomifensine, and the dopamine releasing agent, d-amphetamine, had no effect on D1 receptors. The antidepressant treatments, desipramine, zimeldine, amitriptyline, tranylcypromine, mianserin and ECS and the monoamine reuptake inhibitor, sibutramine, similarly did not alter striatal D1 sites. Thus, of the treatments investigated only chronic receptor blockade by high affinity antagonists altered D1 receptor binding in rat striatum.