Figure 1.

The gut microbiome influences the gut–brain axis through the production of SCFAs, amyloid proteins, LPS, bile acids, and neurotransmitters. SCFAs and bile acids can enter the circulation and have been demonstrated to have an important effect on maintaining BBB homeostasis. Amyloid proteins and LPS can increase local inflammation, promoting further local and systemic protein deposition (A). On the other hand, the CNS can control epithelial permeability, gut motility, and inflammation through the autonomic nervous system and the hypothalamus–pituitary axis (B). Created with Biorender.Com.