LOW BRAIN UPTAKE OF L-[C-11]5-HYDROXYTRYPTOPHAN IN MAJOR DEPRESSION - A POSITRON EMISSION TOMOGRAPHY STUDY ON PATIENTS AND HEALTHY-VOLUNTEERS

The precursor of serotonin, L-5-hydroxytryptophan (L-5-HTP), was radio-labelled with C-11 in the beta-position, yielding [beta-C-11]serotonin after decarboxylation, allowing positron emission tomography studies of L-5-HTP uptake across the blood-brain barrier. We studied 8 healthy volunteers and 6 patients with histories of DSM-III major depression, 2 with repeated examinations after clinically successful treatment. We report a significantly lower uptake of [C-11]5-HTP across the blood-brain barrier in depressed patients, irrespective of phase of illness. The findings emphasize that serotonin is involved in depressive pathophysiology and support earlier suggestions that the transport of 5-HTP across the blood-brain barrier is compromised in major depression.