On the central antiserotonin activity of benzoctamine and opipramol

Benzoctamine inhibited the head twitch reaction induced by L-5-hydroxytryptophan (5-HTP) in mice and by 5-methoxytryptamine (5-MT) in rats pretreated with tranylcypromine. It also antagonized tryptamine (TRP)-induced clonic convulsions of forepaws in rats. Opipramol had no effect in the 5-MT test and appeared to be a weak antagonist in the 5-HTP and TRP tests. Both drugs, of which benzoctamine was a more potent antagonist, inhibited hyperthermia induced by LSD in rabbits. Benzoctamine abolished also LSD-or quipazine-induced stimulation of the flexor reflex in spinal rats; the above effect did not depend on noradrenolytic action of the drug. Opipramol was ineffective as an LSD or quipazine antagonist in this test. These results suggest that benzoctamine blocks the central postsynaptic serotonin receptors. This effect may contribute to the anxiolytic effect of the drug.