The depression scores in both groups were positively correlated with NP level (r = 0.29, P=0.016) and negatively correlated with levels of E (r=0.228, P=0.012), NE (r=0.400, P=0.003), and BDNF (r=0.450, P=0.000, Fig. 3). Here, BDNF is linked to major depressive disorder.