Hedonics of taste influence the gastric emptying in rats

It is known that taste sensation plays important roles in various functions including appetite, nutriental choices, food intake and digestion. To study the modulation of digestive functions by taste stimulation, we measured the gastric emptying of experimental foods with appetitive or aversive tastes in Wistar male rats. Rats were randomly divided into 3 groups: each group was trained to eat a mash mixture (8 g) made up with powdered food (4 g) and a solution (4 g) for 30 min per day. The solution was either distilled water, saccharin solution as a palatable taste, or quinine solution as an aversive taste. On the test day, the contents of the stomach of each rat were measured before and 30, 150, or 300 min after the start of eating the mash. The results showed that the food output from the stomach was increased by the palatable mash and was decreased by the aversive mash in comparison with non-adulterated mash 150 min after eating. There were no significant differences in gastric emptying among the 3 groups after deafferentation of the two peripheral taste nerve branches, the chorda tympani and glossopharyngeal nerves, or after intragastric infusions of each mash. After the establishment of conditioned taste aversions to saccharin, saccharin mash became ineffective in increasing gastric emptying. These results show that hedonically positive tastes increase, but hedonically negative tastes decrease gastric function in terms of gastric emptying.