Both molecules participate in cellular signaling systems that regulate the development and plasticity of neural circuits involved in depression and anxiety (Martinowich and Lu 2008; Castrén and Rantamäki 2010); in addition a variety of cellular and molecular reciprocal interactions between BDNF with the serotonin (5HT) neural system exists (Martinowich and Lu 2008). This evidence concerns the gene BDNF and major depressive disorder.