Considering that the currently available human and animal results have proposed that the enhanced BDNF-TrkB signaling in lymphocytes parallels BDNF-TrkB cortical activity (Wang et al., 2011), our findings suggested that a marked increase in BDNF within plasma by METH exposure contributes to long-lasting behavioral abnormalities (depression and anxiety). The gene discussed is NTRK2; the disease is major depressive disorder.