It has been suggested that dopamine as well as serotonin are associated with the pathophysiology of obsessive-compulsive disorder (OCD). Using iodine-123 labelled N-(3-iodopropen-2-yl)-2β-carbomethoxy-3β-(4-chlorophenyl) tropane ([123I]IPT) single-photon emission tomography (SPECT), we investigated the dopamine transporter (DAT) density of the basal ganglia in patients with OCD before and after treatment with serotonin reuptake inhibitors (SRI). Ten patients with OCD before and after treatment with SRI were included. We performed brain SPECT 2 hours after intravenous administration of [123I]IPT and carried out analyses of the obtained SPECT data, which were reconstructed for the assessment of the specific/non-specific DAT binding ratio in the basal ganglia. We then examined the correlation between the scores of OCD symptoms changes, assessed with Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), and DAT binding ratio.

Patients with OCD after treatment with SRI showed a significantly decreased DAT binding ratio in right basal ganglia compared with pre-treatment. The significant correlation was found between the rates of total scores and compulsion scores changes of the Y-BOCS and the changes of DAT binding ratio of the right basal ganglia. These findings suggest that the dopaminergic neurotransmitter system of the basal ganglia could play an important role in the symptoms improvement of OCD patients.