Chronic administration of desipramine and imipramine but not zimelidine attenuates clonidine-induced depression of avoidance behavior in rats.

Clonidine (CLO) given intraperitoneally in a dose of 0.05 mg/kg decreased the open-field behavior in rats and completely abolished avoidance acquisition. Short term (4 days) administration of desipramine (DMI) and imipramine (IMI) practically failed to change the depressive effects of CLO whilst chronic (21 days) treatment significantly reduced the CLO action on both avoidance and open-field behavior. Contrary to tricyclic antidepressants, zimelidine (ZIM) given either acutely or chronically did not affect the avoidance deficit but given chronically attenuated the CLO-induced sedation in the open field. The results suggest that "classic" tricyclic antidepressants acting strongly upon noradrenaline uptake are more potent in preventing avoidance deficit induced by the alpha 2-adrenoceptor agonist, CLO than drugs acting more selectively upon serotonin uptake.