Effects of rapid tryptophan depletion on brain 5-HT(2) 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-HT(2) receptors using positron emission tomography (PET) and (18)F-labelled setoperone. METHOD Ten healthy women under went 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-HT(2) 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-HT(2) receptors, these findings suggest that a decrease in 5-HT(2) binding following RTD might be an adaptive response that provides protection against depressive symptoms.


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