Clinical and psychometric correlates of dopamine D-2 binding in depression

Background. Single photon emission tomography (SPET) with the dopamine D-2/3 ligand I-123-IBZM gives a semi-quantitative estimate of dopamine binding. In depressed patients, we predicted evidence of reduced function, i.e. increased binding, particularly in more retarded patients. Methods. Fifteen depressed patients with major depressive illness and 15 healthy, age-and sex-matched volunteers were examined with a clinical and neuropsychological test battery and high resolution IBZM-SPET. Estimates for specific binding were computed by averaging striatum to whole slice or frontal uptake ratios over 8-10 scans acquired from 70 min after tracer injection. Results. Using whole slice as reference, left striatal uptake ratios did not significantly differ for patients from controls. Right ratios were significantly higher in patients than controls (P = 0.03). There were significant correlations between IBZM binding in left and right striatum and measures of reaction time and verbal fluency. Conclusions. Increased IBZM binding in striatum probably reflects reduced dopamine function, whether due to reduced release of dopamine, or secondary up-regulation of receptors. The observed abnormalities may be trait or state related, an issue that needs to be addressed with longitudinal study designs. The possible role of medication as a confounding variable requires further exploration.