Nonruminant Nutrition Symposium: Neurogastroenterology and food allergies.

Neurogastroenterology is a subspecialty encompassing relations of the nervous system to the gastrointestinal tract. The central concept is emergence of whole organ behavior from coordinated activity of the musculature, mucosal epithelium, and blood vasculature. Behavior of each effector is determined by the enteric nervous system (ENS). The ENS is a minibrain positioned close to the effectors it controls. The ENS neurophysiology is in the framework of neurogastroenterology. The digestive tract is recognized as the largest lymphoid organ in the body with a unique complement of mast cells. In its position at the "dirtiest" of interfaces between the body and outside world, the mucosal immune system encounters food antigens, bacteria, parasites, viruses, and toxins. Epithelial barriers are insufficient to exclude fully the antigenic load, thereby allowing chronic challenges to the immune system. Observations in antigen-sensitized animals document direct communication between the mucosal immune system and ENS. Communication is functional and results in adaptive responses to circumstances within the lumen that are threatening to the functional integrity of the whole animal. Communication is paracrine and incorporates specialized sensing functions of mast cells for specific antigens together with the capacity of the ENS for intelligent interpretation of the signals. Immuno-neural integration progresses sequentially, beginning with immune detection, followed by signal transfer to the ENS, followed by neural interpretation and then selection of a neural program with coordinated mucosal secretion and a propulsive motor event that quickly clears the threat from the intestinal lumen. Operation of the defense program evokes symptoms of cramping abdominal pain, fecal urgency, and acute watery diarrhea. Investigative approaches to immuno-ENS interactions merge the disciplines of mucosal immunology and ENS neurophysiology into the realm of neurogastroenterology.