Background: We examined striatal dopamine transporter (DAT) distribution volume ratio (DVR) values in subjects with unipolar or bipolar major depressive episode (versus non-depressed healthy volunteers) using the selective DAT radioligand [(99m)Tc]TRODAT-1 and single photon emission computed tomography (SPECT). We hypothesized that striatal DVR values would be greater in depressed versus non-depressed subjects, and that greater DVR values may represent a possible clinical biomarker of depression.
Methods: [(99m)Tc]TRODAT-1 spect images were acquired from 39 depressed and 103 non-depressed drug-free subjects. The primary outcome measure was the DVR value of [(99m)Tc]TRODAT-1 binding for the putamen region and the combined putamen plus caudate region.
Results: DVR values were significantly correlated across all striatal regions within both subject groups (p<0.005). Depressed subjects had significantly greater DVR values (versus non-depressed subjects) in the putamen (p<0.0005) and the combined putamen plus caudate (p<0.0005) regions. There was no difference in DVR values between unipolar (n=24) and bipolar (n=15) depressed subjects, and no difference in DVR values for depressed subjects with or without prior antidepressant exposure. The predictive probability of the putamen or combined putamen plus caudate DVR value to distinguish depressed from non-depressed subjects was significant (p<0.0005).
Limitations: DAT values could potentially be influenced by age, gender, diagnosis, prior psychotropic dug exposure, illness length, or symptom severity.
Conclusion: Results confirm prior observations of greater striatal DAT density in depressed versus non-depressed subjects, and suggest that greater DVR values may possibly represent a potential diagnostic biomarker for distinguish depressed from non-depressed individuals.
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