RT Journal Article SR Electronic T1 Effect of flunarizine and nimodipine on the decrease in tryptophan hydroxylase activity induced by methamphetamine and 3,4-methylenedioxymethamphetamine. JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 586 OP 591 VO 261 IS 2 A1 M Johnson A1 K Mitros A1 D M Stone A1 R Zobrist A1 G R Hanson A1 J W Gibb YR 1992 UL http://jpet.aspetjournals.org/content/261/2/586.abstract AB The effect of calcium channel blockers on the decrease in central tryptophan hydroxylase (TPH) activity and serotonin (5-HT) concentration induced by repeated large doses of methamphetamine (METH) or 3,4-methylenedioxymethamphetamine (MDMA) was evaluated. Rats received four or five injections of METH (10 or 15 mg/kg) or MDMA (10 mg/kg) at 6-h intervals, and were sacrificed 18 to 20 h or 1 week after the last administration. Flunarizine (30 mg/kg) prevented the decline in cortical and neostriatal TPH activity induced by MDMA, but failed to alter the effect of METH. The effect of flunarizine on the METH- and MDMA-induced changes in cortical 5-HT and 5-hydroxyindoleacetic acid concentrations paralleled the changes in enzyme activity. Nimodipine, diltiazem or TA-3090 failed to prevent the MDMA- and the METH-induced decline in TPH activity or in 5-HT and 5-hydroxyindoleacetic acid content. Because haloperidol failed to mimic the protective action of flunarizine, it is unlikely that flunarizine exerts its action by blocking the dopamine D-2 receptors. This study suggests that calcium influx may participate in the MDMA-induced decline in central TPH activity, and that the mechanism by which MDMA and METH decreases TPH activity differs.