Food aversion induced by area postrema ablation

Rats with lesions of the area postrema (APX rats) avoid foods ingested on a regular basis during the period of severe hypophagia immediately following surgery (Tomoyasu & Kenney, 1989). The present work determined whether APX rats would also avoid foods to which they are exposed only after they have recovered from the lesion-induced hypophagia. APX and SHAM-lesion rats were fed a novel food for 8 days beginning at least 1 month after surgery when food intakes (adjusted for body weight) and weight gains of the APX rats had returned to control levels. During 24 h, two-food choice tests, APX rats avoided the food ingested a month after the ablation while avidly ingesting an alternative food, but SHAM rats showed no preference between the foods. There was no indication that this aversion developed by APX rats to foods ingested after recovery from hypophagia is weaker than that developed to foods ingested immediately after the lesion. We conclude that area postrema ablation results in the development of an unconditioned stimulus capable of supporting food-aversion conditioning which remains effective more than 1 month after the ablation. Hence, the relationship between APX-induced food aversion and hypophagia must be indirect and complex. Also, conditioning of food aversions induced by area postrema ablation alone may confound studies of the role of this structure in mediating the development of food aversions after other physiological and/or pharmacological manipulations.