FIGURE 1 | The bidirectional microbiota–gut–brain axis.

From the following article:

The interplay between the intestinal microbiota and the brain

Stephen M. Collins, Michael Surette & Premysl Bercik

Nature Reviews Microbiology 10, 735-742 (November 2012)

doi:10.1038/nrmicro2876

The interplay between the intestinal microbiota and the brain

The neural, immunological, endocrine and metabolic pathways by which the microbiota influences the brain, and the proposed brain-to-microbiota component of this axis. Putative mechanisms by which bacteria access the brain and influence behaviour include bacterial products that gain access to the brain via the bloodstream and the area postrema, via cytokine release from mucosal immune cells, via the release of gut hormones such as 5-hydroxytryptamine (5-HT) from enteroendocrine cells, or via afferent neural pathways, including the vagus nerve. Stress and emotions can influence the microbial composition of the gut through the release of stress hormones or sympathetic neurotransmitters that influence gut physiology and alter the habitat of the microbiota. Alternatively, host stress hormones such as noradrenaline might influence bacterial gene expression or signalling between bacteria, and this might change the microbial composition and activity of the microbiota. DC, dendritic cell; GABA, γ-aminobutyric acid.

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