Novel Biomarkers for Suicidality and Treatment Outcome

Eligibility Details: Inclusion Criteria: 1. Age 18-65 2. Physically healthy and capable of undergoing ketamine infusion 3. Willing and able to provide informed consent 4. Diagnosis of MDE as determined by the MINI (MDD participants) 5. HAM-D 21 score ≥ 16 (MDD participants) 6. Suicide attempt occurred within past 2 weeks (MDD Participants with Suicide Attempt) 7. For the time frame of the past 7 days, C-SSRS score ≥ 3 (MDD Participants without Suicide Attempt, with Suicidal Ideation) 8. For the time frame of the past 7 days, C-SSRS score < 3 (MDD Participants without Suicide Attempt, without SUicidal Ideation) Exclusion Criteria: 1. Pregnancy or lactation 2. Post-partum state (being within 2 months of delivery or miscarriage) 3. Homicide risk as determined by clinical interview 4. A lifetime history of psychotic disorder 5. Any history of dissociation or dissociative disorder 6. Bipolar disorder 7. Pervasive developmental disorder 8. Cognitive disorder 9. Cluster A personality disorder 10. Anorexia nervosa 11. Treatment with one of the following medications, known to affect the glutamate-NMDA receptor system (specifically: lamotrigine, acamprosate, memantine, riluzole, or lithium) 12. Alcohol or drug dependence (except nicotine and caffeine) within the last month or the use of any hallucinogen (except cannabis), including phencyclidine in the last month 13. Any known hypersensitivity or serious adverse effect associated with ketamine treatment 14. Any clinically-significant medication condition or therapy that would preclude treatment with ketamine, to include: Recent myocardial infarction 15. Unstable angina 16. Active neoplasm in the past 6 months 17. Immunosuppressive or corticosteroid therapy within the last month, with the following exceptions: any inhaled, intranasal, topical or vaginal corticosteroids are allowed. 18. Chemotherapy 19. Head injury of loss of consciousness in the past 6 months 20. If the subject reports any of the following disorders: - Rheumatoid arthritis - Lupus erythematosus - Autoimmune hepatitis - Autoimmune peripheral neuropathy - Autoimmune pancreatitis - Behcet's disease - Chrohn's disease - Autoimmune glomerulonephritis - Grave's disease - Guillain-Barre syndrome (if active) - Hashimoto's thyroiditis - Autoimmune polymyositis or polymyalgia (fibromyalgia is OK) - Myasthenia gravis - Narcolepsy - Polyarteritis nodosa - Scleroderma - Sjogren's syndrome - Transverse myelitis - Wegener's granulomatosis - HIstory of seizures (only childhood febrile seizures allowed) - (HIV and Hepatitis are OK if stable) 21. Systolic blood pressure > 150 and/or diastolic blood pressure >90 at screening 22. A QTc > 480 msec as determined by an ECG