Inhibition of SKF 38393- and pergolide-induced circling in rats with unilateral 6-OHDA lesion is correlated to dopamine D-1 and D-2 receptor affinitiesin vitro

Abstract

The effects of 30 dopamine (DA) antagonists, including 4 as stereoisomeric pairs, on circling behaviour induced by the D-1 agonist SKF 38393 and the D-2 agonist pergolide in rats with unilateral 6-hydroxy-DA lesions have been studied. SKF 38393-induced circling was selectively blocked by the specific D-1 antagonists SCH 23390 and SKF 83566, and was furthermore blocked by other DA antagonists with potencies correlating to their affinities to D-1 receptors labelled by³H-SCH 23390in vitro. Pergolide-antagonistic potencies in contrast correlated to affinities to D-2 receptors labelled by³H-spiperonein vitro. Pergolide-induced circling was selectively blocked by the specific D-2 antagonists in the benzamide series. No interaction between D-1 and D-2 antagonists was observed in combination experiments with SCH 23390 and YM 09151-2 in both circling models. Among other reference neurotransmitter antagonists acting onα- andβ-adrenoceptors, histamine, serotonin and muscarinic receptors, only theα ₁-adrenoceptor antagonist prazosin was effective in high doses. In contrast, theα ₂- andβ-adrenoceptor agonists clonidine and clenbuterol as well as the muscarinic agonist RS 86 inhibited circling induced by SKF 38393 as well as pergolide. The 5-HT_1A agonist 8-OHDPAT inhibited pergolide-induced circling only. It is concluded that these two behavioural models are selectivein vivo measures of relative D-1 and D-2 receptor activity of DA antagonists.