LOAD-SENSITIVE RAT GASTRIC VAGAL AFFERENTS ENCODE VOLUME BUT NOT GASTRIC NUTRIENTS

To assess nutrient sensitivity in a population of gastric load-sensiti ve vagal afferents, their neurophysiological activity was examined in anesthetized rats with inflated pyloric cuffs after gastric infusion o f a range of volumes of nutrient and equiosmotic saline solutions. Res ponses to physiological saline loads (1, 2, 4, and 8 ml) were compared with responses elicited by the same volume range of carbohydrate (12. 5% glucose), protein (12.5% peptone), and equiosmotic hypertonic (750 mosM) saline. The threshold load volume of physiological saline requir ed to increase gastric vagal afferent activity was 1 ml. Thereafter, t here was a dose-dependent relationship between increasing gastric volu me and firing rate and between gastric volume and pressure. The dose-r esponse relationships elicited by glucose, peptone, and equiosmotic hy pertonic saline loads did not differ from those elicited by physiologi cal saline loads. These data identify a population of gastric load-sen sitive vagal afferents unresponsive to the chemical composition of gas tric contents and are consistent with a role for vagal gastric volume signals but nut gastric nutrient content in the negative feedback cont rol of ingestion.