Localization of bulk stimuli underlying satiation in Aplysia

The present study was concerned with quantifying and localizing the bulk stimulus that causes satiation in Aplysia. Food deprived animals were found to gain a meal of 15.4 ± 6.6 (S.D.) percent of body weight immediately following a meal of dried seaweed. The weight gain is largely accounted for by water ingested along with the dried seaweed. Animals that were chronically food deprived required a larger amount of food to satiate, compared to animals that had been fed daily; nevertheless after satiation, the mean anterior gut contents were similar in all animals, regardless of the quantity of bulk consumed during the meal. The greater quantity of food eaten by the previously food deprived animals can be quantitatively accounted for by the smaller amount of bulk present in their anterior gut before the meal. Injection of high viscosity non nutritive bulk which preferentially fills the anterior gut was capable of causing satiation whereas injection of low viscosity bulk which preferentially fills the intestine did not cause satiation. Satiation also was not produced by injections of bulk into the hemocoel. The results suggest that satiation in Aplysia is due to activation of mechanoreceptors associated solely with the anterior gut.