In addition to treatment with the investigational drug versus placebo, the study includes a translational neuroimaging component: magnetic resonance spectroscopy (1H-MRS) brain scans are performed at baseline, and then repeated following 1 week of treatment with uridine or placebo. The scans do not use radiation, and are performed on a 3 Tesla MRI system that is approved for clinical use. The scans allow researchers to measure the concentrations of several chemicals in the brain that are may be involved in suicidal ideation.