BDNF and major depressive disorder: Zhang and others discovered that Polygonum sibiricum polysaccharides (PSP) were capable of elevating serum levels of 5-HT and NE, reducing pro-inflammatory cytokine levels in the hippocampus, as well as inhibiting the PI3K/AKT/TLR4/NF-κB and ERK/CREB/BDNF pathways in mice with depression induced by CUMS (Zhang et al., 2023).