This is a multiple-dose study to assess the safety and pharmacology of ABT-436 in physically healthy subjects with mild to moderate depressive symptoms who are not taking any antidepressant medication. Efficacy for treatment of depressive symptoms is not a goal of this study. Fifty subjects will receive study drug for seven days. Thirty subjects will receive ABT-436 and twenty subjects will receive placebo. Blood, urine and saliva samples will be obtained, both before and during study drug administration, to measure ABT-436 pharmacology. Safety will be assessed throughout the study, including at two follow-up visits after completion of study drug administration.