Meal-related stimuli differentially induce c-Fos activation in the nucleusof the solitary tract

Feedback signals arising from the oral cavity and upper gastrointestinal tr act contribute to the control of meal size. To assess how these signals are integrated at central sites involved in ingestive control, we compared lev els of c-Fos activation in the nucleus of the solitary tract (NTS) and area postrema (AP) in response to meal ingestion or gastric and duodenal infusi ons in the rat. Ingestion of a liquid diet to satiety induced significant f os-like immunoreactivity (FLI) at multiple levels of the NTS and within the AP. The restriction of intake to one-half the normal ingestion of a rat di d not result in significant FLI, although gastric infusion of this liquid d iet volume did. Fast bolus infusion resulted in greater FLI than did the sa me volume infused at a rate to mimic that of normal ingestion. Prior experi ence with gastric infusions did not affect the amounts of FLI within the NT S or AP. In rats with pyloric cuffs blocking flow from the stomach to the i ntestine, combined gastric load and duodenal nutrient elicited significantl y greater FLI than either gastric or duodenal infusions alone. These data d emonstrate that neural activation arising from meal-related stimuli are int egrated at the level of the NTS.