 Study intended to determine if there are baseline differences in serum neurosteroid levels and neurotrophic factor BDNF levels in healthy controls vs unmedicated depressed subjects, and whether the levels of these change with antidepressant treatment. Study also intended to determine if baseline neurosteroid BDNF levels, and the change in these levels with treatment, are correlated with clinical antidepressant response to escitalopram Lexapro. 