Modification by clonidine of harmine-induced tremors in mice: involvement of serotoninergic system.

Clonidine exhibited a dose-dependent protection against harmine-induced tremors in mice. This protective effect was not completely blocked by pretreatment with yohimbine. The serotoninergic (5-HT) agonist quipazine and the uptake inhibitor fluoxetine completely antagonized this effect. On the other hand, the 5-HT antagonist cyproheptadine potentiated the protective effect of sub-effective doses of clonidine. These observations suggest a serotonin-mediated action of clonidine in its antitremor action against harmine-induced tremors.