BDNF and major depressive disorder: These studies validate the suggestion that reduction in the intricate dendritic arbor of neurons results in the reduced volume of hippocampus and PFC found in patients with depression. BDNF’s contribution to the dendritic complexity and spine formation has been studied in mutant mice. A gene knockin of BDNF Met polymorphism was created, and studies revealed that having even one copy of this human variant reduces the CA3 apical dendrites in the hippocampus [44].