Meanwhile, insufficient signaling by neurotrophic factors, an important role in neural plasticity, has been considered as a latent factor for depression and antidepressant responses have been observed while neurotrophin signaling promoted (Martinowich et al., 2007; Castrén and Rantamäki, 2010a,b; Autry and Monteggia, 2012; Castrén and Kojima, 2017). Here, BDNF is linked to major depressive disorder.