BDNF and major depressive disorder: Evidence for a role of growth factors in the pathophysiology of depression has come from clinical studies mainly investigating brain derived neurotrophic factor (BDNF), a neurotrophin involved in processes of neuronal maturation, synapse formation and synaptic plasticity (3), and vascular endothelial growth factor (VEGF or VEGFA), an angiogenic factor also possessing neurotrophic and neuroprotective properties (6, 7).