NTF3 and major depressive disorder: As shown in Table 2, the serum levels of BDNF, NT-3, and 5-HT in the depression group were significantly higher than those in the non-depression group and control group (P < 0.05); the serum levels of BDNF, NT-3, and 5-HT in depression group were higher than those in non-depression group and control group, and the level of serum NT-3 in the non-depression group was significantly higher than that in the control group (Fig. 2).