Figure 2.

Illustrative diagram depicting the interconnection between gut and brain. The proposed bidirectional communication is firmly affected by various pathways, including the autonomic nervous system (ANS), hypothalamic–pituitary–adrenal (HPA), immune pathways, enteric nervous system (ENS), endocrine pathways, and neural pathways. Gut microbiota can produce microbial metabolites that activate the neuroenteric plexus, stimulate neuropeptide production in the brain, and increase gut–blood barrier and blood–brain barrier (BBB) permeability. The brain releases molecules that stimulate the function of the gut and neuroendocrine plexus.