BDNF and major depressive disorder: In the CUMS model, matrine regulates the microbiota-gut-brain axis, improves the disorder of intestinal flora and metabolites, restores intestinal permeability, reduces intestinal inflammation, reduces the level of pro-inflammatory cytokines, and increases the level of BDNF in the brain, thereby alleviating depression-like behavior in mice, which is manifested by increasing SPT sugar water consumption, reducing FST and OFT immobility time, and shortening the latency period of NSFT (Zhang et al., 2023).