[Brain-gut interactions]

Our digestive tract has an autonomous functioning but also has a bidirectional relation with our brain known as brain-gut interactions. This communication is mediated by the autonomous nervous system, i.e., the sympathetic and parasympathetic nervous systems, with a mixed afferent and efferent component, and the circumventricular organs located outside the blood-brain barrier. The vagus nerve, known as the principal component of the parasympathetic nervous system, is a mixed nerve composed of 90% afferent fibers, which has physiological roles due to its putative vegetative functions. The vagus nerve has also anti-inflammatory properties both through the hypothalamic pituitary adrenal axis (through its afferents) and the cholinergic anti-inflammatory pathway (through its efferents). The sympathetic nervous system has a classical antagonist effect on the parasympathetic nervous system at the origin of an equilibrated sympathovagal balance in normal conditions. The brain is able to integrate inputs coming from the digestive tract inside a central autonomic network organized around the hypothalamus, limbic system and cerebral cortex (insula, prefrontal, cingulate) and in return to modify the autonomic nervous system and the hypothalamic pituitary adrenal axis in the frame of physiological loops. A dysfunction of these brain-gut interactions, favoured by stress, is most likely involved in the pathophysiology of digestive diseases such as irritable bowel syndrome or even inflammatory bowel diseases. A better knowledge of these brain-gut interactions has therapeutic implications in the domain of pharmacology, neurophysiology, behavioural and cognitive management.