Simultaneous determination of 5-hydroxytryptamine, its amino acid precursors and acid metabolite in discrete brain regions by high-performance liquid chromatography with fluorescence detection.

L-Tryptophan, 5-hydroxytryptophan (5-HTP), 5-hydroxytryptamine, and 5-hydroxyindoleacetic acid (5-HIAA) from discrete regions of brain can be resolved by isocratic elution on a C-18 reversed-phase column and quantitated by native fluorescence measurement. This method is rapid and simple and can reproduceably detect 5-hydroxytryptamine, tryptophan and 5-HIAA with picogram sensitivity. The detection of 5-HTP in brain extracts from untreated animals is difficult because of the extremely low endogenous levels of 5-HTP. Quantitation of 5-HTP presents no problem in animals injected with 5-HTP or with an inhibitor of L-aromatic amino acid decarboxylase. Brain tissue requires minimal treatment for assay and the hydroxyindoles are stable enough to allow automated processing.