Ontogenetic differences in CS palatability following conditioned taste aversion training

Abstract

Five- and 15-day-old rats learned to reject a 15% sucrose solution when it was paired with LiCl, footshock, or citric acid solution. Aversions were matched across conditioning with the various reinforcers in terms of amount consumed during test (Experiment 1). Subsequent comparisons of conditioned changes in orofacial and other behavioral responses to the sucrose CS (Experiment 2) were performed to assess ontogenetic, qualitative, and functional differences in the aversions established. The 15-day-olds reacted to LiCl-conditioned sucrose as if it were distasteful by displaying paw treading and wall climbing during test, whereas they did not exhibit such responses to footschock- or citric acid-conditioned sucrose. Five-day-olds did not show this pattern of differentiation. They appeared to react similarly to sucrose infusion independent of the US used during conditioning. The present results indicate age-related differences in the acquisition and/or expression of conditioned taste aversions when different USs are employed. However, quality of the US was not the only factor that varied when conditioning with the different reinforcers. It is possible that changes in other parameters such as CS duration, US duration, or number of conditioning trials experienced rather than differences in US consequence could have contributed to the observed results. Generally, the 15-day-olds behaved similarly to adults whereas the 5-day-olds did not. Although conclusions are still tenative, a developmental shift in the mechanism for learning flavor aversions is suggested.