BDNF and major depressive disorder: The results of the present study show that (1) TRD patients had lower plasma BDNF concentrations than healthy controls, but their BDNF concentration was similarly decreased in other drug-free MDD patients; (2) TRD patients continued to have low plasma BDNF concentrations after BLT; however, (3) while BLT did not affect BDNF concentration in the entire TRD group, responders and remitters with TRD had significantly higher post-treatment plasma BDNF concentrations than nonresponders and nonremitters, respectively.