the authors investigated the cerebral metabolism of tryptophan in patients suffering from malignant pain by means of csf dosage of tryptophan ( trp ) , 5-hydroxytryptophan ( 5-htp ) , serotonin ( 5-ht ) and 5-hydroxyindoleacetic acid ( 5-hiaa ) .
C0041249
tryptophan
C0000578
5-htp