Disassociation between Preprandial Gut Peptide Release and Food-Anticipatory Activity

Animals learn to anticipate a meal as evidenced by increases in premeal activity. This learned response appears to be independent of the nutrient status of an animal because food-anticipatory activity (FAA) can be seen after entrainment by a highly palatable food when rats remain ad libitum on chow. Mealtime feeding not only induces an increase in activity but also appears to entrain the secretion of various peptides prior to a meal including insulin, ghrelin, and glucagon-like peptide-1 (GLP-1). It is not clear whether these meal-anticipatory changes in peptides are causally associated with FAA. To assess whether FAA and preprandial peptide changes co-occur with meal entrainment using different diets, rats were conditioned to receive a 6-h chow meal, 6-h high-fat meal, or 2 h access of chocolate while ad libitum on chow in the middle of the light cycle. FAA was measured for 4 h prior to mealtime. Rats were then killed at 90, 60, and 30 min prior to mealtime and plasma was collected. Although the chocolate-entrained rats showed comparable FAA with the nonchocolate-entrained animals, they did not show anticipatory increases in the ghrelin or GLP-1. All entrainment conditions induced a decrease in insulin and an increase in glucose prior to mealtime. These data suggest that separate mechanisms may underlie the preprandial increases in ghrelin and GLP-1 and changes in FAA, insulin, and glucose.