The central action of pizotifen.

The central action of the potential antidepressant drug pizotifen (Sandomigran) was studied in mice, rats and rabbits. Pizotifen in doses up to 10 mg/kg i.p. was ineffective in classic tests for antidepressant activity. It neither antagonized the effects of reserpine in rats (hypothermia, ptosis) nor potentiated the effects of amphetamine (in mice and rats), nialamide or L-dopa (in mice) on locomotor activity. However, its antidepressant activitiy was found in the 'despair test' in rats. On the other hand, pizotifen inhibited the head twitch reaction induced by L-5-hydroxytryptophan in mice (ED50 = 0.009 mg/kg, i.p.) and by 5-methoxytryptamine (+ tranylcypromine) in rats (ED50 = 0.45 mg/kg, i.p.). It also antagonized tryptamine-induced clonic convulsions of fore-paws in rats (ED50 = 0.35 mg/kg, i.p.), and in doses of 5--10 mg/kg s.c. inhibited hyperthermia produced by LSD in rabbits. Finally, pizotifen (0.1--0.3 mg/kg, i.v.) inhibited or abolished LSD- or quipazine-induced stimulation of the hind limb flexor reflex of spinal rats; the above effect was not due to noradrenolytic action of the drug. These results suggest that pizotifen strongly blocks the central postsynaptic serotonin receptors.