Duodenal preabsorptive origin of gustatory alliesthesia in rats

Facial consummatory responses reflecting ingestive and aversive perceptions were studied and quantified in rats chronically implanted with gastric, duodenal, and oral catheters. A gustatory stimulus of 50 microliters of 1.75 mol/l sucrose was injected into the mouth every 5 min for 65 min. At time 0, 0.5 ml containing 0.3 g glucose was injected into the stomach or into the duodenum. Typical ingestive facial consummatory responses were observed in response to sweet stimuli prior to the load. Aversive consummatory responses were observed in response to sweet stimuli after the glucose duodenal load (negative alliesthesia). The gastric load of glucose was not followed by negative alliesthesia in response to sweet oral stimuli. In the last part of the experiment the rats were vagotomized. When the rats were subjected again to the same gustatory sessions, the duodenal load was followed by weak and delayed negative alliesthesia in response to sweet stimuli. These results in rats parallel results obtained in human subjects and reinforce the hypothesis of the existence of a duodenal preabsorptive signal for alimentary alliesthesia. They also suggest that the vagus nerve plays a part in the perception of satiety.