Tryptophan Hydroxylase and Tyrosine Hydroxylase Activity in Rat Brain1

multiple doses ofmethamphetamine on tryptophan hydroxylase and tyrosine hydroxylase activity in rat brain. J. Pharmacol. Exp. Ther. 214: 257-262, 1980. Tryptophan hydroxylase (TPH) activity was measured in various rat brain regions after administering large doses of metham-phetamine (METH). After four sequential doses of METH (15 mg/kg), given every 6 hr, TPH activity was decreased (to approximately 1 0 % of control) in both the neostriatum and hippocampus. The depression of enzyme activity persisted for at least 30 days. When compared with the depression of neostriatal tyrosine hydroxylase activity, the depression of neostriatal and hippocampal TPH activity occurred sooner and was more pronounced. The depression of TPH activity was dependent on the number of doses and the amount of drug administered. Five days after one to two doses of METH,