Brain–Gut–Microbiota Axis

Patients frequently report that stress causes or exacerbates gastrointestinal (GI) symptoms, indicating a functional relationship between the brain and the GI tract. The brain and GI tract are closely related embryologically and functionally, interacting in various ways. The concept of the brain-gut axis was originally established in the 19th and early 20th centuries based on physiological observations and experiments conducted in animals and humans. In recent years, with the growing recognition that gut microbiota plays a vital role in human health and disease, this concept has been expanded to the brain-gut-microbiota axis. The brain influences the motility, secretion, and immunity of the GI tract, with consequent effects on the composition and function of the gut microbiota. On the other hand, gut microbiota plays an essential role in the development and function of the brain and enteric nervous system. Although knowledge of the mechanisms through which the gut microbiota influences distant brain function is incomplete, studies have demonstrated communication between these organs through the neuronal, immune, and endocrine systems. The brain-gut-microbiota axis is an essential aspect of the pathophysiology of functional GI disorders such as irritable bowel syndrome, and is also involved in other GI diseases, including inflammatory bowel disease. This review summarizes the evolving concept of the brain-gut-microbiota axis and its implications for GI diseases, providing clinicians with new knowledge to apply in clinical practice.