It has been shown that direct injection of BDNF into the dentate gyrus or CA3 subfield of the hippocampus exerts an antidepressant effect and the antidepressant-like effect mediated by paroxetine is enhanced in rodent models of depression [138,139]; enhanced BDNF signaling enhances mood [140,141]. The gene discussed is BDNF; the disease is depressive disorder.