BDNF and major depressive disorder: The first module controls the downstream GRIA1, GRIN2A, GSK3A, CREB3, BDNF, FOS, ATF2, MAPK8, MAPK14, JUND, RHOA, and other genes to treat depression through ADCYAP1R1--GNAS--ADCY1—Camp--PRKACA/RAPGEF3 cascade reactions.