Elevated putamen D2 receptor binding potential in major depression with motor retardation:: An [11C] raclopride positron emission tomography study

Objective: Several antidepressants raise striatal dopamine, but the role of striatal dopamine during major depressive episodes is unclear. Striatal [C-11] raclopride binding potential measured with positron emission tomography is an index of D-2 type receptors and is sensitive to extracellular dopamine levels (higher D-2 binding potential occurs when dopamine is lower). It was hypothesized that putamen D-2 binding potential would be higher during major depressive episodes featuring motor retardation. Method: Drug-free, nonsmoking subjects experiencing a major depressive episode (N=21) underwent [C-11] raclopride PET imaging as did 21 healthy age-matched comparison subjects. Motor retardation was measured with the finger tapping test. Results: The depressed subjects exhibiting motor retardation had significantly higher D-2 binding potential in both the left and right putamen than did healthy subjects, and putamen D-2 binding potential correlated significantly with motor speed in the depressed subjects. Conclusions: The results argue that extracellular dopamine is lower in subjects experiencing a major depressive episode that features motor retardation. This depression subtype should preferentially benefit from dopamine-increasing medications and should be targeted in future clinical trials of dopamine reuptake inhibitors.