The intensity of a fetal taste aversion is modulated by the anesthesia used during conditioning.

Rat fetuses (E18) can learn a taste aversion in utero if experience with a sweet flavor (saccharin = Sac) is followed by a malaise-producing injection of lithium chloride (LiCl). Here we report that this phenomenon can be significantly modulated by the type of anesthesia administered to the pregnant dam before the conditioning procedure. Dams were anesthetized with one of the following drugs or drug combinations: (1) sodium pentobarbital; (2) ketamine hydrochloride and xylazine; or (3) sodium pentobarbital and ketamine hydrochloride. While under the influence of these anesthetics, rat fetuses received pairings of Sac + LiCl or one of the following sets of oral and systemic (i.p.) control injections: Sac + Saline, H2O + LiCl; H2O + Saline. At age 15 days neonatal rats were given a taste preference test by allowing them to select nipples painted with either saccharin or vehicle (H2O). After weaning, rats were given an additional taste preference test where they were allowed to drink from bottles filled with either 0.30% saccharin or water. Neonates that received Sac + LiCl injections avoided saccharin-painted nipples while neonates that received control injections in utero preferred saccharin-painted nipples. Rats that acquired the taste aversion under the influence of ketamine showed a significantly stronger conditioned taste aversion on the nipple preference test than did those from dams injected with sodium pentobarbital. The conditioned taste aversion was not detectable later during the bottle preference test. Since ketamine blocks N-methyl-D-aspartate (NMDA) glutamate receptors, and these receptors have been implicated in neural plasticity during development, our data suggest that NMDA antagonism can potentiate fetal learning. Ketamine has been used as an obstetrical and pediatric anesthetic.(ABSTRACT TRUNCATED AT 250 WORDS)