EFFECTS OF RAPID TRYPTOPHAN DEPLETION IN PATIENTS WITH SEASONAL AFFECTIVE-DISORDER IN REMISSION AFTER LIGHT THERAPY

Background: Previous studies show that rapid tryptophan depletion reve rses the effects of therapy with serotonergic, but not noradrenergic, antidepressant drugs in patients with remitted nonseasonal depression. The objective of this study was to investigate the effects of rapid t ryptophan depletion in patients with seasonal affective disorder (SAD) that was in clinical remission after light therapy. Methods: Patients who met DSM-III-R criteria for recurrent major depressive episodes, s easonal (winter) pattern (equivalent to SAD), were treated with a stan dard course of light therapy. Ten patients with SAD in clinical remiss ion after light therapy underwent rapid tryptophan depletion in a plac ebo-controlled, double-blind crossover study. Behavioral ratings and p lasma tryptophan levels were obtained before and after rapid tryptopha n depletion. Results: Plasma total and free tryptophan levels were sig nificantly reduced to 20% of normal levels by the rapid tryptophan dep letion. The depletion session resulted in significant increases in dep ression scores compared with the sham control session. Six of 10 patie nts had a clinically significant relapse of their depression following the tryptophan depletion session. Conclusions: Rapid tryptophan deple tion appears to reverse the antidepressant effect of bright light ther apy in patients with SAD. This suggests that the therapeutic effects o f bright light in SAD may involve a serotonergic mechanism.