Aversive behavior during intraoral intake in male rats.

We investigated if the taste of a sucrose solution becomes progressively more aversive during intraoral infusion and if this contributes to the termination of the intake in male rats. The display of aversive behavior, such as gapes and chin rubs, but not headshakes, forelimb flails or orofacial grooming, varied with the concentration of an intraorally infused solution of quinine hydrochloride (QHCl) and increased by the time the rat rejected an intraorally infused 2 M solution of sucrose. Activation of gapes and chin rubs by brief intraoral infusion of QHCl advanced the rejection of the sucrose solution if given late during intraoral infusion, but blockade of gaping by anaesthesization of the oral cavity with Xylocain did not prolong the intake of the sucrose solution. Headshakes and forelimb flails could be elicited by stimulating the head and limbs with sucrose, and gapes and chin rubs were activated by infusion of a 2 M solution of sucrose into the stomach or duodenum but not by infusion of glucose into the jugular or hepatic portal vein. Preventing filling of the gastrointestinal tract during intraoral infusion of sucrose (sham feeding) eliminated the display of gapes and chin rubs. It is suggested that an increase in the aversiveness of the taste of a sucrose solution contributes to the rejection of that solution during intraoral infusion. However, rats can reject a sucrose solution in the absence of any behavioral sign of aversion and none of the so-called "taste-related" aversive behaviors is exclusively dependent upon stimulation of the taste receptors in the oral cavity.