Low brain uptake of L‐[11C]5‐hydroxytryptophan in major depression: a positron emission tomography study on patients and healthy volunteers

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Abstract
The precursor of serotonin, L‐5‐hydroxytryptophan (L‐5‐HTP), was radiolabelled with 11C in the β‐position, yielding [β‐11C]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 [11C]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.