It was found that early life stress lowers BDNF and alters stress sensitivity later in life (Cirulli et al., 2009), whereas increases in BDNF, either via social enrichment or direct infusion into the brain, was found to reduce susceptibility to depression-like behavior (Siuciak et al., 1997; Cirulli et al., 2010). Here, BDNF is linked to depressive disorder.