Abstract
The gastrointestinal tract is colonized with more than 1014 microorganisms that weigh more than 1 kg. Such microbes are in close contact with the largest mass of lymphoid tissue in the body, the gut-associated lymphoid tissue, and thereby provide the principal driving force in postnatal maturation of the mammalian immune system. In addition to such effects, some previous studies have shown that psychological stress might disrupt the integrity of the intestinal microflora and thereafter contribute to the pathological process of gastrointestinal disorders. Recently, we demonstrated that postnatal microbial colonization programs the hypothalamic-pituitary-adrenal system for stress response in mice. These results indicate a novel link between intestinal flora and the nervous system and show a new aspect of the brain-gut axis.
