Facial consummatory responses in rats support the ponderostat hypothesis

Facial consummatory responses reflecting ingestive and aversive perceptions were studied and quantified in rats chronically implanted with gastric and oral catheters. A gustatory stimulus of 50 microliters of 1.75 mol.1-1 sucrose was injected into the mouth every 5 min during 60 min. At time zero, 1.7 ml of 3.3 mol.1-1 glucose was injected into the stomach. Typical ingestive facial consummatory responses were observed in response to sweet stimuli prior to the gastric load. Aversive consummatory responses were observed in response to sweet stimuli after the glucose gastric load (negative alliesthesia). The rats were then fasted until they had lost about 14% of their body weight (from 411 +/- 34 g to 353 +/- 28 g). When lean, the rats were subjected to the same gustatory session as in the control period described above. In lean rats 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 fed ad lib and they recovered their initial body weight. When the rats were subjected again to the same gustatory sessions, the gastric load was followed by negative alliesthesia in response to sweet stimuli. Thus, after recovering their initial body weight, the rats displayed the same response as in the control sessions prior to losing weight. These results in rats parallel results obtained in human subjects, and reinforce the hypothesis of the existence of a ponderostat regulating body mass.