Glutamatergic and GABAergic Mediators of Antidepressant Response in Major Depression

Inclusion Criteria:

1. Male or female age ≥ 18 and ≤ 65
2. Meets DSM-IV93 criteria for MDD
3. Current score of ≥ 18 on the 21-item Hamilton Depression Rating Scale (HAM-D).94

Exclusion Criteria:

1. Unwillingness or inability to provide written informed consent
2. Current suicidal ideation
3. Active psychotic symptoms
4. Lifetime history of bipolar disorder, schizophrenia, or OCD
5. Failed treatment with an adequate trial of ≥ 2 antidepressants during the current major depressive episode ("failure" will be defined as ≤ 50% subjective improvement, and an "adequate trial" will be defined as at least 4 weeks of treatment using at least the minimum dose of the antidepressant recommended by the manufacturer in product labeling)
6. DSM-IV diagnosis of alcohol or substance dependence, with the exception of nicotine dependence, within three months prior to screening
7. Any history of treatment with electroconvulsive therapy
8. Positive urine toxicology screen for any drug of abuse or excluded medication at screening
9. Clinically significant medical or neurologic disease, as judged by the principal investigator, which would increase the risk to the participant or interfere with interpretation of results
10. Female participants with a positive urine pregnancy test at screening
11. Pregnancy. Females of childbearing potential must be using an effective contraceptive method (e.g., abstinence, prescription oral contraceptives, contraceptive injections, double-barrier method, male partner sterilization).
12. Any screening laboratory abnormality deemed clinically significant by the investigator
13. Use of any excluded medications (see Section 6.7 below) that cannot be discontinued during the screening phase
14. Previous failure to respond to treatment with citalopram that would, in the judgment of the investigator, constitute an adequate trial in MDD
15. Treatment with any investigational medications within 30 days prior to screening
16. Any contraindications to having an MRI scan, including cardiac pacemakers, metal vascular clips or stents, artificial heart valves, certain kinds of prostheses, brain stimulator devices, implanted drug pumps, ear implants, eye implants or known metal fragments in eyes, exposure to shrapnel or metal filings (wounded in military combat, sheetmetal workers, welders, and others), transdermal drug delivery systems, and certain tattoos with metallic ink