It has been proposed that an impairment of synaptic plasticity (neurogenesis, axon branching, dendritogenesis and synaptogenesis) in brain areas such as the hippocampus, may be a central element in the pathophysiology of depression and that these neural plasticity alterations may be related to abnormal levels of neurotrophic factors, specifically BDNF [33]. This evidence concerns the gene BDNF and major depressive disorder.