Glutamate and Opioid Mechanisms of Antidepressant Response to Ketamine

The study is a randomised, double-blind, crossover design with two treatment conditions: oral placebo or oral naltrexone preceding ketamine infusion during neuroimaging in subjects with treatment-resistant depression. Each subject will participate in two imaging sessions on two separate days. Each subject will receive a dose of ketamine (IV infusion, 0.5 mg/kg over 40 minutes) during each scan. Subjects will receive either oral placebo or naltrexone 50 mg, 45 minutes before the initiation of each of the ketamine infusions.