BDNF and major depressive disorder: Recent studies suggest that chronic treatment with the SSRIs fluoxetine or sertraline increased hippocampal neurogenesis, ameliorated cognitive deficits, and depression-like behavioral symptoms in R6/1 mice (Grote et al., 2005; Renoir et al., 2012) and increased BDNF levels and neurogenesis in R6/2 mice (Peng et al., 2008).