On the mode of action of six putative dopamine receptor agonists on suppression of exploratory behaviour in rats.

The effects of six putative dopamine receptor agonists on exploratory behaviour in rats were assessed: pergolide, (+)- and (-)-3-PPP, bromocriptine, mesulergine and CQ 32-084. Behaviour was automatically recorded in a holeboard apparatus and the data were analysed by the novel multivariate statistical method of partial least squares. All six substances suppressed exploratory behaviour at low doses. Pergolide and (+)-3-PPP-induced stereo-typed behaviour at higher doses. The suppression of exploration induced by pergolide was completely antagonised by sulpiride, partly antagonised by metoclopramide and weakly affected by haloperidol pretreatment. The effects of a low dose of (+)-3-PPP, bromocriptine or CQ 32-084, but not (-)-3-PPP or mesulergine, were antagonised by sulpiride. These findings support the hypotheses that pergolide, (+)-3-PPP, bromocriptine and CQ 32-084 inhibit exploration via stimulation of dopamine receptors. The present data do not substantiate the hypothesis that the suppression of exploration induced by (-)-3-PPP is mediated by stimulation of dopamine autoreceptors. A detailed analysis of the dose curves for pergolide and (+)-3-PPP indicates that the latter compound may have effects in addition to those of a dopamine receptor agonist.