<i>Lacticaseibacillus rhamnosus</i> KY16 Improves Depression by Promoting Intestinal Secretion of 5-HTP and Altering the Gut Microbiota

Increasing research suggests a connection between gut microbiota and depressive disorders. Targeted changes to the intestinal flora may contribute to alleviating anxiety and depression. This study aimed to identify probiotics that could attenuate stress-induced abnormal behavior and explore potential mechanisms. The administration of LR.KY16 significantly reduced stress-induced abnormal behaviors and physiological dysfunction. The mechanism may be via regulating the structure of the intestinal microbiota in mice, increasing the abundance of <i>Akkermansia muciniphila</i>, prompting enterochromaffin cells to secrete 5-HTP in the gut, which enters the brain through the bloodstream and promotes the synthesis of 5-HT in the brain, and then activates brain-derived neurotrophic factor (BDNF)/tyrosine kinase receptor B (TrkB) through the 5-HT1A receptor. In addition, LR.KY16 also increased the expression of claudin-7, occludin, and zonula occludens-1 (ZO-1) in the colon, inhibited microglial M1 polarization, and inhibited systemic inflammation.