Background. Single photon emission tomography (SPET) with the dopamine
D-2/3 ligand I-123-IBZM gives a semi-quantitative estimate of dopamin
e binding. In depressed patients, we predicted evidence of reduced fun
ction, 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 clini
cal 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 probab
ly reflects reduced dopamine function, whether due to reduced release
of dopamine, or secondary up-regulation of receptors. The observed abn
ormalities may be trait or state related, an issue that needs to be ad
dressed with longitudinal study designs. The possible role of medicati
on as a confounding variable requires further exploration.