EFFECTS OF TRYPTOPHAN DEPLETION IN FULLY REMITTED PATIENTS WITH SEASONAL AFFECTIVE-DISORDER DURING SUMMER

Background. Deficiencies in brain serotonin function are believed to p lay an important role in the pathophysiology of seasonal affective dis order/winter type (SAD). However, no direct evidence has been reported so far that lowered brain serotonin activity causes the symptoms of S AD. Methods. We studied 11 SAD patients who had suffered recurrent win ter depressive episodes of SAD and were fully recovered and off treatm ent during the summer. In a randomized, balanced, double-blind crossov er design patients received two amino acid beverages, one containing t ryptophan and the other containing no tryptophan but otherwise identic al. Behavioural ratings and plasma total and free tryptophan concentra tions were assessed at baseline before administration of the amino aci d beverages and at several time points afterwards. Results. The trypto phan-free amino acid beverage induced significant decreases of plasma total and free tryptophan levels and both levels increased during sham depletion (condition x time interaction: P < 0.001). Tryptophan deple tion, but not sham depletion caused a transient return of depressive s ymptoms (condition x time interaction: P < 0.001). Conclusions. The pr esent study demonstrates that SAD patients in remission during the sum mer are vulnerable to a return of depression when depleted of tryptoph an. This finding supports the importance of serotonergic mechanisms in the pathophysiology of SAD.