Monoamine metabolism in human prefrontal cortex and basal ganglia. Pet studies using [β‐11C] l–5‐hydroxytryptophan and [β‐11C] L‐dopa in healthy volunteers and patients with unipolar major depression

The 11C-labelled precursors for serotonin and dopamine synthesis, [β-11C] L-5-hydroxytryptophan (5-HTP) and [β-11C] L-DOPA, were employed as tracer ligands using positron emission tomography (PET) for the evaluation of their regional brain utilization. Study objects were fifteen healthy volunteers and eight patients suffering from, primary RDC unipolar major depression. Specific utilizations of [11C] 5-HTP and [11C] L-DOPA were detected in medial aspects of the prefrontal cortex (PFC) and in the basal ganglia. Utilization of[11C], but not [11C] L-DOPA, was significantly further increased in lower areas of the medial PFC in depressive illness. There were no differences between volunteers and patients with respect to specific utilization within basal ganglia. Alterations in utilization of [11C]5-HTP and [11C] L-DOPA in the medial PFC may reflect the degree of activation of serotonergic and dopaminergic cell bodies in the mesencephalic nuclei, suggesting mesencephalocortical regulation. Earlier, we have reported a decrease in the uptake of [11C] 5-HTP over the blood-brain barrier in depressed patients compared with healthy volunteers. A hypothetic activation of serotonin synthetic capacity, topographically limited to the medial PFC and relevant to depressive illness, might represent a pathophysiological compensation related to serotonin precursor deficiency. However, the sum of events may still result in a state that does not exclude a serotonergic hypofitnction in major depression. Depression 1:71–81 (1993). © 1993 Wiley-Liss, Inc.