BDNF and depressive disorder: The prefrontal cortex is involved in the regulation of mood and stress (Jia et al., 2015), and changes in the expression of BDNF and 5-HT in the prefrontal cortex have been implicated in the pathophysiology of depression (Gibney et al., 2013; Yu et al., 2015) and the therapeutic effect of antidepressants (Engel et al., 2013).