Alterations in extracellular tryptophan and dopamine concentrations in rat striatum following peripheral administration of d- and l-tryptophan: An in vivo microdialysis study

Incorporation profiles of d-Trp and l-Trp into the striatum following intraperitoneal (i.p.) administration of d-Trp or l-Trp in male Sprague-Dawley rats (100 mg/kg) were investigated by using a brain microdialysis technique. Alterations in the extracellular dopamine (DA) concentration in the rat striatum were also examined. Incorporation profiles of d-Trp and l-Trp were almost identical; however, transient DA release was only observed 0–30 min following d-Trp administration. Pretreatment with 3-methylpyrazole-5-carboxylic acid, an inhibitor of d-amino acid oxidase (DAAO), significantly suppressed the DA release induced by d-Trp. These findings suggest that d-Trp-induced DA release may be mediated by certain d-Trp metabolites produced by DAAO.