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 wi th a sweet flavor (saccharin = Sac) is followed by a malaise-producing injection of lithium chloride (LiCl). Here we report that this phenom enon can be significantly modulated by the type of anesthesia administ ered 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 infl uence of these anesthetics, rat fetuses received pairings of Sac + LiC l or one of the following sets of oral and systemic (i.p.) control inj ections: Sac + Saline, H2O + LiCl; H2O + Saline. At age 15 days neonat al 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 a llowed to drink from bottles filled with either 0.30% saccharin or wat er. Neonates that received Sac + LiCl injections avoided saccharin-pai nted nipples while neonates that received control injections in utero preferred saccharin-painted nipples. Rats that acquired the taste aver sion under the influence of ketamine showed a significantly stronger c onditioned taste aversion on the nipple preference test than did those from dams injected with sodium pentobarbital. The conditioned taste a version was not detectable later during the bottle preference test. Si nce ketamine blocks N-methyl-D-aspartate (NMDA) glutamate receptors, a nd these receptors have been implicated in neural plasticity during de velopment, our data suggest that NMDA antagonism can potentiate fetal learning. Ketamine has been used as an obstetrical and pediatric anest hetic. Thus, the data presented here may have clinical implications as well.