Effects of rapid tryptophan depletion on brain 5-HT2 receptors:: a PET study

Background The mechanism by which rapid tryptophan depletion (RTD) paradigm induces depressive relapse in recently remitted patients with depression is unknown. Aims To determine the effects of RTD on brain 5-HT2 receptors using positron emission tomography (PET) and F-18-labelled setoperone. Method Ten healthy women underwent two PET scans. Each scan was done 5 h after the ingestion of either a balanced or a tryptophan-deficient amino acid mixture, and the two test sessions were separated by at least 5 days. Results The RTD decreased plasma free tryptophan levels significantly but it had no significant effects on mood. Subjects showed a significant decrease in brain 5-HT2 receptor binding in various cortical regions following the RTD session. Conclusions When taken with the evidence that antidepressant treatment is associated with a decrease in brain 5-HT2 receptors. these findings suggest that a decrease in 5-HT2 binding following RTD might be an adaptive response that provides protection against depressive symptoms. Declaration of interest None.