Expert's view: Vassilia Theodorou about the brain-gut axis
Vassilia THEODOROU is the Director of Research of the Neuro-Gastroenterology and Nutrition Unit at INRAE Toxalim, France.
The brain-gut axis is quite a new concept that we are starting to get familiar with in human medicine. Could you please briefly introduce the concept?
I agree with you that we are speaking a lot recently about the brain-gut axis, but the concept is not so recent. The brain-gut axis is an integrated bidirectional communication between the gut and the brain through the connection of the enteric nervous system located in the gut wall, and the autonomous nervous system. In this way, messages are conveyed from the gut to the brain and back to the gut. What is more recent in this bidirectional communication is the involvement of gut microbiota as a new player in this dialogue, modulating signals in the intestinal barrier received by the enteric nervous system.
What is the role of the intestinal microbiota on the occurrence of human diseases? Do you think we can find similarities in production animals?
The symbiotic relationship between the gut microbiota and the host is present not only in humans but also in production animals. This symbiotic relationship can be disturbed, leading to what we used to call dysbiosis.1 Dysbiosis is linked to pathogenicity. For instance, infection by pathogens or intestinal inflammation leads to dysbiosis and disease. However, even if dysbiosis is closely linked to disease in several human pathologies, we do not know yet what comes first, the egg or the hen.
How does stress (under different types) influence the physiology of the gut?
There is a large body of literature underlying the effects of stress on gut functions. For instance, it is well known that stress accelerates intestinal transit, modifying intestinal motility. It is also well known that stress disrupts the integrity of the intestinal barrier function resulting in increased gut permeability, alterations of mucus secretion, and modifications of the microbiota profile. The activation of the hypothalamic-pituitary-adrenal axis activates the adrenergic system and secretes catecholamines by the adrenals, which, in a cascade of events, can influence the different actors of the intestinal barrier function.
Could we expect modifications of animal behavior under stressful conditions? Is this response different from chronic and acute stress?
Modifications of animal behavior under chronic or acute stress are obvious. In rodent experimental models, it has been shown that even in early life, stress can be translated into behavioral changes later in life and disturbed gut functions. In a pig model, it has been shown that piglets reared in an enriched environment (reared in houses with free outdoor access) before weaning exhibit less aggressive behavior when they become older and show a delayed occurrence of puberty versus piglets reared in indoor standard conditions. These studies show the long-lasting effects on behavior and physiology.
What is the role of probiotics on this topic, can they modulate barrier function and prevent intestinal dysbiosis?
Absolutely! Here again, based on a large body of literature, probiotics have been shown to be able to reduce gut hyperpermeability that is induced by stress or inflammation. This reinforcement of the gut barrier results in less upload of luminal agents, less mucosal immune activation, and, consequently, less nerve activation.
1Dysbiosis is defined as an “imbalance” in the gut microbial community that is associated with disease. This imbalance could be due to the gain or loss of community members or changes in relative abundance of microbes. (from Messer et al., Physiology of the Gastrointestinal Tract (Sixth Edition), 2018)