BDNF and Parkinson disease: Probiotics are live microorganisms that are beneficial to the health of the host when given in appropriate amounts, and preclinical and clinical studies have shown that probiotics regulate gut microbiota (improving intestinal barrier integrity, reducing overgrowth of potentially pathogenic bacteria in the gut, and inhibiting bacterial translocation), maintain immune homeostasis (regulating the immune system of the gastrointestinal mucosa), protect DN (inhibiting glial cell activation, increasing BDNF and SCFAs, and reducing LPS), and improve the overall PD behavioral phenotype (146).