Effects of hypothermia on the acquisition of conditioned taste aversion in rats.

Abstract

The mechanism of conditioned taste aversion (CTA) was analyzed by subjecting rats to reduced body temperature during various phases of CTA acquisition. A 15 min access to .1% saccharin served as the conditioned stimulus (CS), and an i.p. injection of LiCl (.15 M, 4% of body wt) given 30 min later served as the unconditioned stimulus (US). Hypothermia (cooling to 20-22.degree. C colonic temperature) alone or combined with anesthesia (Nembutal 20 or 40 mg/kg) did not prevent CTA acquisition when applied during the CS-US interval. Hypothermia induced immediately after LiCl administration to anesthetized or unanesthetized rats failed to disrupt CTA or to increase neophobic rejection of saccharin. On the other hand, the hypothermic animals were not able to form the short-term gustatory trace when the CS (2% saccharin, 1% of body wt) was injected i.p., although this procedure yielded significant CTA in euthermic rats. The most vulnerable link of CTA acquisition is the formation of the short-term gustatory trace. Persistence of the short-term trace, its association with poisoning and consolidation of the permanent CTA engram are accomplished by mechanisms that are resistant to hypothermia and/or anesthesia.