Effect of 1-(m-trifluoromethylphenyl)-piperazine on 3H-serotonin binding to membranes from rat brain in vitro and on serotonin turnover in rat brain in vivo.

1-(m-Trifluoromethylphenyl)-piperazine inhibited the specific binding of tritiated serotonin to membranes from rat brain in vitro at lower concentrations than did quipazine or MK-212 (6-chloro-2-[1-piperazinyl]-pyrazine). In rats 1-(m-trifluoromethylphenyl)-piperazine decreased the concentration of 5-hydroxyindoleacetic acid (5-HIAA) without altering the concentration of serotonin in whole brain. The decrease in 5-HIAA was apparently due to a decrease in serotonin turnover, since 1-(m-trifluoromethylphenyl)-piperazine caused a slower decline in serotonin concentration after synthesis inhibition by alpha-propyldopacetamide and a slower accumulation of 5-HIAA after probenecid injection to block its efflux from brain. The decrease in serotonin turnover is an expected result of stimulating serotonin receptors in brain and has earlier been reported to occur with quipazine. Thus all of the results are compatible with the idea that 1-(m-trifluoromethylphenyl)-piperazine acts as a serotonin receptor agonist in rat brain.