Safety and Pharmacodynamic Study of ABT-436 in Major Depressive Disorder

Inclusion Criteria 1\. Age between 18 to 55 years, inclusive. 2. Body Mass Index is 20 to 35 kg/m2, inclusive. 3. A primary Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition, Text Revision (DSM-IV-TR) diagnosis of major depressive disorder. 4\. Mild-to-moderate depressive symptoms at Screening. 5. A condition of general good physical health. Exclusion Criteria 1. Pregnant or breast-feeding female. 2. Use of any medication within 4 weeks prior to Day -2, unless the dose has been stable for 4 weeks, no dose change is anticipated during the study, and the medication is specifically allowed for this study, OR prior as needed (PRN) use of the medication is specifically allowed for this study. 3. Use of fluoxetine or aripiprazole within 8 weeks prior to Day -2. 4. Positive screen for drugs of abuse/alcohol, recent history of drug/alcohol abuse or smoking. 5. A current or past history of major depressive disorder with psychotic features, bipolar disorder, schizophrenia or other psychotic disorder, mental retardation, or mental disorder due to a general medical condition.