Naloxone-precipitated conditioned taste aversions in morphine-dependent Fischer (F344) and Lewis rat strains

The Fischer 344 (F344) and Lewis (LEW) rat strains are genetically divergent populations that are used to study the effects of and responses to drugs of abuse. These strains have been reported to differ in their somatic responses to morphine withdrawal. To address possible strain differences in the affective response to withdrawal, the present study assessed the ability of naloxone-precipitated withdrawal from morphine to induce conditioned taste aversions in male F344 and LEW rats. Subjects were given morphine to induce dependence and then given access to a novel saccharin solution followed by naloxone. Pairings were given for two conditioning trials after which subjects were given access to saccharin without naloxone administration to assess extinction of the aversion. Both strains acquired aversions to the naloxone-associated taste with no significant differences in the rate of acquisition. Differences appeared during extinction with LEW animals extinguishing the taste aversion significantly faster than F344 animals.