Gastrointestinal inflammation by gut microbiota disturbance induces memory impairment in mice

In this study, we tested our hypothesis regarding mechanistic cross-talk between gastrointestinal inflammation and memory loss in a mouse model. Intrarectal injection of the colitis inducer 2,4,6-trinitrobenzenesulfonic acid (TNBS) in mice caused colitis via activation of nuclear factor (NF)-κB and increase in membrane permeability. TNBS treatment increased fecal and blood levels of lipopolysaccharide (LPS) and the number of Enterobacteriaceae, particularly Escherichia coli (EC), in the gut microbiota composition, but significantly reduced the number of Lactobacillus johnsonii (LJ). Indeed, we observed that the mice treated with TNBS displayed impaired memory, as assessed using the Y-maze and passive avoidance tasks. Furthermore, treatment with EC, which was isolated from the feces of mice with TNBS-induced colitis, caused memory impairment and colitis, and increased the absorption of orally administered LPS into the blood. Treatment with TNBS or EC induced NF-κB activation and tumor necrosis factor-α expression in the hippocampus of mice, as well as suppressed brain-derived neurotrophic factor expression. However, treatment with LJ restored the disturbed gut microbiota composition, lowered gut microbiota, and blood LPS levels, and attenuated both TNBS- and EC-induced memory impairment and colitis. These results suggest that the gut microbiota disturbance by extrinsic stresses can cause gastrointestinal inflammation, resulting in memory impairment.