Extinction of a newly acquired conditioned taste aversion: Effect of gustatory CS administered under anaesthesia

Gustatory stimuli administered by intraperitoneal injection of concentrated flavour to anaesthetized rats cannot be associated with subsequent poisoning, but can extinguish an earlier established conditioned taste aversion (CTA). The differential sensitivity of CTA acquisition and extinction processes to anaesthesia was used to examine their interaction in the early stages of CTA learning. Male, hooded rats maintained on a 24-h water deprivation schedule were offered 15-min access to 0.1% saccharin (CS), were immediately afterwards anaesthetized with sodium pentobarbital and poisoned 30 min later by intraperitoneal injection of LiCl (US, 0.15 M, 2% body weight). Saccharin intake during a second presentation of the CS on the following day served as a measure of retention. Intraperitoneal injection of 2% saccharin (1% body weight) applied in the middle of the CS-US interval or 1 h after US administration did not decrease the CTA strength. Saccharin administered 2, 3, 4, and 5 h after US caused a gradually increasing CTA extinction which was almost complete with the 5-h interval and slightly decreased with the 24-h delay. The failure of the saccharin injection applied 1 h after US to extinguish the newly acquired CTA is not due to coincidence of the gustatory stimulus with the continuing symptoms of poisoning, since LiCl administration preceding saccharin injection does not prevent CTA extinction in rats with well established CTA. It is concluded that the post-acquisition gradient of extinction reflects the decay of the short-term gustatory trace established during the initial saccharin drinking.