Neuroleptic drugs block both the hyperactivity and the increase in caudate nucleus cyclic AMP concentration produced by the administration of tranylcypromine and L-dopa to rats.

Injection of rats with tranylcypromine and L-dopa increased brain dopamine concentrations and produced a behavioural syndrome that includes hyperactivity. It also elevated caudate nucleus cyclic AMP concentrations by approximately 50% in vivo, probably by stimulating dopamine receptors. Pretreatment with chlorpromazine inhibited both the tranylcypromine/L-dopa-induced behaviour and elevated cyclic AMP concentrations in a dose-dependent manner. Haloperidol and alpha-flupenthixol also inhibited both effects, while beta-flupenthixol and pimozide were without effect. Since none of these drugs altered the tranylcypromine/L-dopa-induced rise of brain dopamine, it is likely that they produced their effect by inhibiting dopamine-sensitive adenylate cyclase. A good correlation was found to exist between the neuroleptic inhibition of both the increased behavioural activity and the increased caudate nucleus cyclic AMP concentrations produced by tranylcypromine and L-dopa.