Dextromethorphan-Bupropion on Striatal Activity in Adults With Major Depressive Disorder

Dextromethorphan-bupropion (DXM/BUP) is a novel, rapid-acting, glutamatergic antidepressant approved by the US FDA in the treatment of adults with MDD, with clinical evidence of antidepressant effect within two weeks of administration. This pilot, two-week, open-label neuroimaging study will examine the effect of DXM/BUP on striatal activity in adults with major depressive disorder (MDD). The region of interest is the striatum, a core structure in the human reward circuit. Adults with a primary diagnosis of MDD currently experiencing a moderate-severe major depressive episode will receive open-label DXM/BUP (150 mg orally, twice daily) for 14 days. Task-based functional MRI scans will be conducted at baseline (Day 1, prior to treatment) and at primary endpoint (Day 14, following treatment) to evaluate changes in striatal activation. During each scan, participants will perform the Effort Expenditure for Rewards Task (EEfRT), a validated measure of reward motivation and effort-based decision-making that is particularly sensitive to anhedonia. Changes in striatal activation associated with open-label DXM/BUP treatment in adults with MDD will be evaluated by comparing pre-treatment and post-treatment fMRI blood-oxygenation level-dependent (BOLD) measures.