Effects on mood of acute phenylalanine/tyrosine depletion in healthy women.

Catecholamines have been implicated in the etiology and pathophysiology of mood and anxiety disorders. In the present study, we investigated the effects of experimentally reducing catecholamine neurotransmission by means of acute phenylalanine/tyrosine depletion (APTD). Healthy female volunteers ingested: (1) a nutritionally balanced amino acid (AA) mixture (n = 14); (2) a mixture deficient in the serotonin precursor, tryptophan (n = 15); or (3) one deficient in the catecholamine precursors, phenylalanine and tyrosine (n = 12). Mood was measured at three times: at baseline and both immediately before and after an aversive psychological challenge (public speaking and mental arithmetic) conducted 5 hours after AA mixture ingestion. Acute tryptophan depletion (ATD) lowered mood and energy and increased irritability scores. These effects were statistically significant only after the psychological challenge. The effect of APTD on mood was similar to that of ATD. APTD did not attenuate the anxiety caused by the psychological challenge. These findings suggest that, in healthy women, reduced serotonin and/or catecholamine neurotransmission increases vulnerability to lowered mood, especially following exposure to aversive psychological events.

A comparison of the effects of acute tryptophan depletion and acute phenylalanine/tyrosine depletion in healthy women.

Acute tryptophan depletion (ATD), which is thought to lower serotonin levels, can result in a lowering of mood. In the present study we compared the effect of ATD with acute phenylalanine/tyrosine depletion (APTD) in healthy women. Although considerable evidence relates catecholamines to the regulation of anxiety, there was no difference in anxiety responses in the ATD and APTD groups when the women underwent a mildly stressful psychological challenge. Both ATD and APTD caused a similar lowering of mood. Both depletions also increased heart rate. These results suggest that APTD is a useful method for studying the effect of low catecholamine levels in humans, and that catecholamines are involved in the regulation of mood.