Dopamine D₂ receptor availability and amphetamine-induced dopamine release in unipolar depression

Background: Reduced dopaminergic transmission has been implicated in the pathophysiology of major depression. The aim of the present study was to measure striatal D₂ receptor availability and amphetamineinduced dopamine release in nonpsychotic, unmedicated, unipolar patients during an episode of major depression. Methods: The striatal equilibrium specific to nonspecific partition coefficient (V₃″) of the D₂ receptor antagonist [¹²³I]IBZM was measured with single photon emission computerized tomography before and after amphetamine administration in 9 depressed subjects and 10 matched healthy control subjects. Results: No significant differences were observed in preamphetamine D₂ receptor availability between depressed patients (0.73 ± 0.08) and control subjects (0.78 ± 0.10, p = .23). Amphetamine-induced reduction in [¹²³I]IBZM V₃″ (ΔV₃″) was similar in depressed patients (-9.8 ± 5.5%) and control subjects (-7.8 ± 2.5%, p = .32). Amphetamine induced a transient improvement in symptomatology in depressed patients, but this improvement did not correlate with [¹²³I]IBZM ΔV₃″. Conclusions: This study did not replicate previously reported alterations in striatal D₂ receptor density in depressed patients and suggests that stimulant-induced dopamine release is not altered in major depression.