BDNF and mood disorder: Further increased pro-inflammatory cytokines (Dahl et al., 2014) and reduction of neurotrophins (Biggs et al., 2010; Peltz et al., 2011) in the hippocampus are related to mood disorders as well as synaptic connections in the PFC and hippocampus are decreased by chronic stress exposure, which reduces the local expression of BDNF in animals (Duman and Monteggia, 2006).