BDNF and major depressive disorder: The proposition that cognitive impairment in MDD may be the result of progressive neurotoxic and neuroinflammatory processes, as well as volumetric reductions in neuroanatomical areas such as the hippocampus, striatum, and fronto-cingulate cortices [126, 156–161], suggests the modulation of neurosteroid, neurotrophin and pro-inflammatory cytokine activity might be useful targets for treatment development [126, 162–165].