The-pole of gastrointestinal vagal afferents in the control of food intake: Current prospects

Meals are the functional units of food intake in humans and mammals, and ph ysiologic approaches to understanding the controls of meal size have demons trated that the presence of food in the upper gastrointestinal tract plays a critical role in determining meal size. The vagus nerve is the primary ne uroanatomic substrate in the gut-brain axis, transmitting meal-related sign als elicited by nutrient contact with the gastrointestinal tract to sites i n the central nervous system that mediate ingestive behavior. This article describes progress in examining the role of the vagal gut-brain axis in the negative-feedback control of meal size from four perspectives neuroanatomi c, neurophysiologic, molecular, and behavioral. Vagal afferents are strateg ically localized to be sensitive to meal-related stimuli, and their central projections are organized viscerotopically in the caudal brainstem. Vagal afferents are sensitive to mechanical, chemical, and gut and peptide meal-r elated stimuli and can integrate multiple such modalities. Meal-elicited ga strointestinal stimuli activate distinct patterns of c-fos neural activatio n within caudal brainstem sites, where gut vagal afferents terminate. Resul ts of selective chemical and surgical vagal deafferentation studies have re fined our understanding of the sites and types of critical gastrointestinal feedback signals in the control of meal size. Recent behavioral, molecular , and neurophysiologic data have demonstrated brainstem sites where central ly acting neuropeptides may modulate the processing of gut vagal afferent m eal-related signals to alter feeding. Investigations of the structure and f unction of splanchnic visceral afferents and enterics and characterization of the integrative capacities of the hindbrain and forebrain components of the gut-brain axis are critical next steps in this analysis. Nutrition 2000 ;16:866-873. (C) Elsevier Science Inc. 2000.