Figure 1.

Key components of brain gut microbiota axis. A network of specialized target/transducer cells in the gut wall functions as an interface between the organism and the gut lumen. In response to external and bodily demands, the brain modulates individual cells (ECC, enterochromaffin cells; SMC, smooth muscle cells; ICC, interstitial cells of Cajal) within this network via the branches of the autonomic nervous system (ANS) (sympathetic and parasympathetic/vagal efferents) and the hypothalamic pituitary adrenal (HPA) axis. Such modulation can be transient (e.g., in response to transient perturbations) or longlasting (in response to chronically altered brain output). The microbiota is in constant bidirectional communication with this interface via multiple signaling pathways, and this communication is modulated in response to perturbations of the microbiota, or the brain. The integrated output of the brain gut microbial interface is transmitted to the brain via multiple afferent signaling pathways, including endocrine and neurocrine (vagal, spinal afferents) pathways. While acute alterations in this interoceptive feedback result in transient functional brain changes, chronic alterations are associated with neuroplastic brain changes.” (8).