title: L-tyrosine contributes to (+)-3,4-methylenedioxymethamphetamine-induced serotonin depletions.
abstract: The specific mechanisms underlying (+)-3,4-methylenedioxymethamphetamine (MDMA)-induced damage to 5-HT terminals are unknown. Despite the hypothesized role for dopamine (DA) and DA-derived free radicals in mediating this damage, it remains unclear why MDMA produces long-term depletions of 5-HT in brain regions that are sparsely innervated by DA neurons. We hypothesized that the precursor to DA biosynthesis, tyrosine, mediates MDMA-induced 5-HT depletions. Extracellular tyrosine concentrations increased fivefold in striatum and 2.5-fold in hippocampus during the administration of neurotoxic doses of MDMA. In vitro results show that L-tyrosine can be hydroxylated nonenzymatically to the DA precursor l-3,4-dihydroxyphenylalanine (DOPA) under pro-oxidant conditions. The local infusion of L-tyrosine into the striatum or hippocampus during MDMA administration potentiated the acute increase in extracellular DA and the long-term depletion of 5-HT after MDMA. Coinfusion of the aromatic amino acid decarboxylase (AADC) inhibitor m-hydroxybenzylhydrazine attenuated these effects in hippocampus and decreased basal extracellular DA in the striatum. In contrast, the reverse dialysis of the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine into the hippocampus did not affect MDMA-induced increases in extracellular DA or the long-term depletion in 5-HT. These results show that MDMA increases the concentration of tyrosine in the brain to cause a long-term depletion of 5-HT via the nonenzymatic, tyrosine hydroxylase-independent, hydroxylation of tyrosine to DOPA and subsequently to DA via AADC. Overall, the findings suggest that MDMA depletes 5-HT by increasing tyrosine and its eventual conversion to DA within 5-HT terminals.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Breier
authors.forename: Michael G
authors.initials: MG
authors.lastname: Bankson
authors.forename: Bryan K
authors.initials: BK
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D004357:Drug Synergism; D007276:Injections, Intraventricular; D008297:Male; D018817:N-Methyl-3,4-methylenedioxyamphetamine / Q000008:administration & dosage*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000008:administration & dosage*; D014443:Tyrosine / Q000008:administration & dosage* / Q000502:physiology*
chemical_list: D012702:Serotonin Antagonists; D012701:Serotonin; D014443:Tyrosine; D018817:N-Methyl-3,4-methylenedioxyamphetamine