Conditioned taste aversion to injected flavor: differential effect of anesthesia on the formation of the gustatory trace and on its association with poisoning in rats.

Anesthesia disrupts formation of conditioned taste aversion (CTA) when induced before presentation of the gustatory stimulus but does not prevent association of the already formed gustatory trace with delayed poisoning. The transition between the disruption-prone and disruption-resistant phases of CTA acquisition was examined under conditions eliminating the confounding effect of anesthesia on ingestive behavior. Intraperitoneal injection of 2% saccharin (1% b.wt.) was used as an intravascular gustatory conditioned stimulus (CS) followed 2 h later by the visceral unconditioned stimulus (US) (LiCl 0.15 mol/l, 2% b.wt.). Pentobarbital anesthesia (50 mg/kg) prevented CTA formation when applied 4 h before to 30 min after saccharin injection, but was ineffective in the second half of the CS-US interval (1-2 h after saccharin administration). CTA acquisition was also impaired by subanesthetic dosages of pentobarbital (10 and 20 mg/kg) preceding i.p. injection of saccharin. It is concluded that the abrupt disappearance of the disruptive effect of pentobarbital in the middle of the CS-US interval marks the formation of the gustatory trace which mediates CTA learning even when both CS and US are applied by i.p. injection.