The alteration of BDNF levels, as well as the imbalance between pro-BDNF and m-BDNF, and deficits in BDNF signaling are associated with the pathogenesis of various neurologic and psychiatric disorders, including depressive disorder, schizophrenia, and bipolar disorder [8,11,23,38,39,40,41]. Here, BDNF is linked to bipolar disorder.