BDNF and depressive disorder: Some studies have reported that depression caused by chronic stress disrupts the BDNF–tropomyosin related kinase B (TrkB) receptor signaling pathway in the PFC and hippocampus, and ultimately contributes to impaired synaptic maturation, synaptic protein synthesis, and glutamate receptor cycling (Collingridge et al., 2010; Duric et al., 2010; Hoeffer and Klann, 2010; Christoffel et al., 2011; Duman and Voleti, 2012).