For example, the flavonoid leucovorin has been shown to reduce pro-inflammatory cytokine levels (118) and has recently been shown to enhance the TrkB/BDNF pathway, and stimulate FGF/FGFR1 signaling, which helps up-regulate the expression of BDNF, promote the differentiation of NCSs and neuronal growth, and also provide a new therapeutic strategy for MDD (119). This evidence concerns the gene NTRK2 and major depressive disorder.