A serotonergic component in the central action of 1-(o-methoxyphenyl)-piperazine.

1-(o-methoxyphenyl)-piperazine (o-MPP) is regarded as an antagonist of the dopamine receptor. Its effects were studied for the hind limb flexor reflex in the spinal rat, the body temperature in rats maintained at ambient temperature of 28 degrees C and stereotypy induced in rats by a low dose of apomorphine (0.5 mg/kg). o-MPP (2-12.5 mg/kg) stimulated the flexor reflex and, in higher doses (10-40 mg/kg), elevated the body temperature of heat-adapted rats. Both effects were inhibited by central serotonin receptor blocking agents--cyproheptadine or metergoline. Low doses of o-MPP (below 5 mg/kg) did not affect stereotypy induced by apomorphine; higher doses (5-25 mg/kg) attenuated the stereotypy in a dose-dependent manner. The results obtained suggest that o-MPP may facilitate the central serotonergic transmission similarly as several other phenylpiperazines. The role of this effect in the "antidopamine" action of o-MPP is discussed.