NTF3 and major depressive disorder: Recently, it has been proposed that decreased neurotrophic factor production, increased glutamate-induced intracellular calcium concentration, and abnormal intracellular signal transduction mechanisms related to neuroplasticity by cortisol via the hypothalamic-pituitary-adrenocortical (HPA) axis are also thought to be the cause of depression (Jacobson and Sapolsky, 1991; Nibuya et al., 1995; Manji et al., 2001; Sanacora et al., 2008).