Lack of behavioral effects of monoamine depletion in healthy subjects

This study was designed to determine the behavioral effects of a reduction in catecholamine and indoleamine function in healthy subjects. Eight healthy subjects received the tyrosine hydroxylase inhibitor, alpha-methyl-para-tyrosine (AMPT) in combination with a full-strength tryptophan-depleting amino acid drink during one 4-day test session, and AMPT and tryptophan-supplemented amino acid drink (n = 2), or a 25% strength tryptophan-depleting amino acid drink (n = 6) during a second 4-day test session. The combined administration of AMPT and the tryptophan-free amino acid drink did not produce statistically significant or even clinically noticeable changes in mood among the healthy subjects. The implications of these observations for the monoamine hypotheses of depression are discussed.