BDNF and major depressive disorder: The innate inflammatory cascade has been shown to increase glutamate neurotransmission, central sensitization, and excitotoxicity, reduce BDNF and neurogenesis, and activate neurodegenerative cascades, events observed in both depression and pain conditions (for review, see Dantzer et al., 2011; Maes et al., 2011; Song and Wang, 2011; Zunszain et al., 2013; Walker et al., 2014).