Tryptophan depletion in lithium-stabilized patients with affective disorder

Central serotonergic function abnormalities are thought to be associated with the pathogenesis of affective disorder. Reduced serotonergic function, induced by tryptophan depletion, has in several studies transiently reversed the antidepressant effect of SSRIs in depressed patients in remission. Serotonergic pathways are suggested to be of importance in the mechanisms of the action of lithium. The purpose of this study was to investigate whether the stabilizing effect of lithium is dependent on short-term availability of serotonin. Tryptophan depletion was induced in thirty patients with affective disorder (20 bipolar and 10 unipolar), all stabilized on lithium treatment for at least one year. The study was performed using a randomized, double-blind, controlled design. Plasma tryptophan was reduced by 80% in the experimental group and 16% in the control group. However, no clinically relevant mood changes were observed. Transient reduction in serotonergic function does not seem to affect mood in affective-disorder patients stabilized on lithium treatment.