BDNF and major depressive disorder: Preclinical behavioral investigations have shown that the deletion of 5-HT1A heteroreceptors in the dentate gyrus granule cells of the hippocampus abolished the positive effects of SSRIs in various tasks and attenuated the neuroplastic effects associated with their administration via a reduction in the expression of the brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) [122], which further demonstrates their importance for treatment of depression.