Sedative action of low doses of dopaminergic agents

The activity of rats receiving low doses of dopaminergic agonists and neuroleptics was tested in the "open-field" test. Apomorphine, piribedil, L-DOPA, and nomifensine given at low doses (1-500 mug/ig) depressed the activity of animals. Spiperone and chlorpromazine given at low doses increased the activity, particularly in respect of one of the parameters investigated: the time of walking. Low doses of pimozide, haloperidol, and fluphenazine did not affect measurably the animal behavior. Spiperone counteracted the sedation induced by low doses of apomorphine, piribedil, and nomifensine. Chlorpromazine prevented the sedation produced by apomorphine. In the rats with a lesion of the substantia nigra only nomifensine retained its sedative action, while apomorphine and piribedil ceased to produce it. The reported results further support the hypothesis about the existence and the role of dopaminergic autoreceptors.