Background: Despite growing evidence for involvement of the dopaminergic system in obsessive-compulsive disorder (OCD), the functional anatomy of the dopaminergic system in the basal ganglia has been investigated sparsely.
Methods: Dopamine D(2) receptor binding was assessed in 10 medication-free OCD patients and 10 healthy control subjects, matched for age, gender, and handedness. The binding potential was measured with single photon emission computerized tomography (SPECT) and infusion of the D(2) receptor radiotracer [(123)I] iodobenzamide. With magnetic resonance imaging as reference, regions of interest (caudate and putamen) were delineated for each hemisphere and coregistered with the corresponding SPECT scans.
Results: Dopamine D(2) receptor binding in the left caudate nucleus was significantly lower in the patients with OCD than in healthy control subjects [F(1,18) = 7.0, p =.016]. In addition, an interhemispheric difference was observed in the patient sample. Both the D(2) receptor binding potential (df = 9, p =.012), and the volume (df = 9, p =.029) of the left caudate nucleus were statistically significantly reduced relative to the right caudate nucleus.
Conclusions: This study provides in vivo evidence for abnormalities in the binding potential of the dopamine D(2) receptor, which suggest the direct involvement of the dopaminergic system in the pathophysiology of OCD.