UNEXPRESSED MORPHINE CONDITIONED SALT AVERSION - PROCEDURAL VARIANTS AND HYPERTONICITY OF SALT

Previous work has demonstrated that rats that received a sodium chlori de (salt) solution paired with a high dose of morphine do not directly express a conditioned salt aversion (decreased intake) in a one-bottl e test. Importantly, lithium conditioned salt aversions and morphine c onditioned saccharin aversions are readily expressed. The present stud y examined two possible accounts of the failure for morphine condition ed sail aversion to be directly expressed. Experiment 1 eliminated an account based on procedural variations that were uncontrolled in the o riginal salt and saccharin conditioning protocols (Bevins et al., 1996 ). Experiment 2 eliminated a hypertonic account that argues that the h igh concentrations of salt in the previous work (1% and greater) inter fered with direct expression of salt aversion by inducing continual dr inking. Rats given a non-hypertonic salt solution (0.3%) paired with m orphine still did not express a salt aversion in a one-bottle test. A two-bottle testing procedure, however, revealed a robust salt aversion with the non-hypertonic solution. (C) 1997 Elsevier Science B.V.