Elevated Putamen D ₂ Receptor Binding Potential in Major Depression With Motor Retardation: An [ ¹¹ C]Raclopride Positron Emission Tomography Study

Objective: Several antidepressants raise striatal dopamine, but the role of striatal dopamine during major depressive episodes is unclear. Striatal [ ¹¹ C]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 [ ¹¹ C]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.