DIFFERENTIAL EFFECTS OF THREE DOPAMINE AGONISTS: APOMORPHINE, BROMOCRIPTINE AND LERGOTRILE

Abstract— The ergolines are a new class of proposed dopamine receptor agonists, whose efficacy in treatment of Parkinsonism is under investigation. In order to explore the mechanisms of their action. two ergolines (bromocriptine and lergotrile) were compared to apomorphine for in vivo effects on behavior and in vitro effects on uptake and release of [³H]dopamine by brain minces. Inhibition of dopamine synthesis in vivo significantly interfered with both bromocriptine‐ and lergotrile‐induced stereotypy, while apomorphine‐induced stereotypy was not affected. Significant differences among the compounds were also seen neurochemically: bromocriptine inhibited the release of [³H]dopamine. while lergotrile increased release. Apomorphine did not affect uptake or release of [³H]dopamine. The results, of both behavioral and neurochemical experiments, suggest that two ergolines enhance dopaminergic function by action on presynaptic dopaminergic sites in addition to receptor agonism.