Effects of heat stress on intestinal tract and cognitive function

Heat stress refers to a series of stress reactions such as heat balance disturbance and physiological dysfunction when the body is exposed to the thermal environment for a long time. Studies have found that heat stress can damage intestinal morphology, such as length of intestinal villi, number of goblet cells, and depth of the crypt, affecting the digestion and absorption functions. It also can increase the permeability of the intestinal barrier by damaging the tight junction of the intestinal epithelium, which in turn allows endotoxin and bacteria to enter the blood circulation from the intestinal cavity to cause a systemic inflammatory response. At the same time, heat stress can disrupt the homeostasis of intestinal microbiota, increase pathogenic bacteria, and change downstream metabolites such as short-chain fatty acids. In addition, heat stress can inhibit the occurrence of hippocampal neurons and reduce the number of neurons; decrease the density of synapses; damage important organelles of neurons; induce inflammation of the central nervous system, and then lead to cognitive dysfunction. The brain-gut axis is a two-way signal axis between the intestine and the brain. Intestinal microorganisms and the intestinal barrier can participate in central nervous system regulation, and the brain can change the intestinal homeostatic function and affect the quality of the intestinal barrier through the hypothalamic-pituitary-adrenal axis (HPA axis). The interaction plays an essential role in the body's homeostasis. Therefore, this article reviewed current understandings on the impacts of heat stress on the gut and cognitive function, aiming to provide a reference for subsequent research.