Several recent studies demonstrated that peripheral (serum and/or plasma) BDNF levels are lower in patients suffering from mood disorders during manic/mixed and depressive episodes compared to matched healthy controls and that effective treatments are able to normalize them (Dell'Osso et al., 2010; Fernandes et al., 2011; Lin, 2009; Piccinni et al., 2008, 2009, 2015; Polyakova et al., 2015; Sen, Duman, & Sanacora, 2008). Here, BDNF is linked to mood disorder.