Fig. 2

Influences of the gut microbiota on different components in the CNS. a The byproducts of bacterial metabolism in gut, SCFAs, are able to induce proliferation of Foxp3⁺ Tregs through histone-modification. Administration of specific strains of microbiota or metabolite promotes the development of Th1, Th17 cells, and other cytokines. b Gut microbiota contribute to the maturation progress of naïve microglia and the number of mature microglia decreases in the absence of microbiota while the total count of microglia remains the same. Amp-sensitive microbiota catalyze dietary tryptophan to AHR agonists which could bind to the AHR on astrocyte and induce anti-inflammatory effects. c Deletion of gut microbiota leads to neurogenesis in hippocampus in animals raised in GF conditions or treated with antibiotics. d BBB in GF mice are more permeable with decreased expression of tight junction proteins while the integrity of BBB could be restored by colonization of microbiota or supplementation of SCFAs. Vagus nerve is a critical component linking biological functions in gut and brain. Signals from gut could either directly interact with vagus nerve or indirectly through the mediation of EECs and hormonal factors