Antiparkinsonian potential of interaction of LEK-8829 with bromocriptine

The ergoline derivative, LEK-8829 (9,10-didehydro-N-methyl-(2-propynyl)-6-methyl-8-aminomethylerg oline), has been proposed as a potential atypical antipsychotic drug with antagonistic actions at dopamine D2 and serotonin 5-HT2 and 5-HT1A receptors (Krisch et al., 1994, 1996). LEK-8829 also induces contralateral turning in rats with 6-hydroxydopamine-induced unilateral lesion of dopamine nigrostriatal neurons. Turning is blocked by SCH-23390 (R(+)-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzaze pine), a dopamine D1 receptor antagonist. It has been suggested that LEK-8829 could have beneficial effects in parkinsonian patients suffering from psychotic episodes induced as a side-effect of antiparkinsonian treatment with dopamine D2 receptor agonists. Therefore, we now investigated the interaction of LEK-8829 with the dopamine D2 receptor agonist bromocriptine (2-bromo-alpha-ergokryptine) in 6-hydroxydopamine-lesioned rats. Treatment with either LEK-8829 (3 mg kg(-1)) or bromocriptine (3 mg kg(-1)) induced a vigorous contralateral turning response. The cumulated number of turns induced by the treatment with both drugs combined was not significantly different from the cumulated number of turns induced by single-drug treatment. The pretreatment with SCH-23390 (1 mg kg(-1)) did not have a significant effect on the bromocriptine-induced turning but significantly decreased the turning observed after the combined LEK-8829/bromocriptine treatment. We conclude that in the 6-hydroxydopamine model, the turning behaviour mediated by the LEK-8829/bromocriptine combination may be the result of opposing activity of both drugs at dopamine D2 receptors with concomitant stimulation of dopamine D1 receptors by LEK-8829. Therefore, LEK-8829 may have a potential for the therapy of parkinsonism complicated by dopamine D2 receptor agonist drug-induced psychosis.