BDNF and depressive disorder: The brain derived neurotrophic factor-extracellular regulated protein kinase (BDNF-ERK/AKT-CREB) signaling cascade plays an important role in the pathophysiology of depression, and is critical for hippocampal neurogenesis (Gourley et al., 2008; Lee and Son, 2009; Castren and Rantamaki, 2010).