Low level of dopaminergic D2 receptor binding in obsessive-compulsive disorder

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 forage, gender, and handedness. The binding potential was measured with single photon emission computerized tomography (SPECT) and infusion of the D-2 receptor radiotracer [I-123] 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 CCD 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.