Modulation of ethanol reinforcement by conditioned hyperthermia

The present study was designed to determine whether a signal for availability of self-administered ethanol would acquire the ability to elicit a conditioned thermal response and to alter ethanol self-administration. Non-deprived male albino rats (n=8) were exposed to a differential conditioning procedure in which brief (30-min) periods of access to sweetened ethanol on a fixed-ratio operant schedule were either signalled (CS+ trials) or unsignalled (Blank + trials). A different stimulus signalled trials on which barpressing was not reinforced (CS- trials). Body temperature was recorded continuously from implanted telemetry devices. As in previous studies involving experimenter-administered ethanol injections, the stimulus paired with self-administered ethanol (CS+) acquired the ability to elicit a conditioned increase in body temperature. Moreover, barpressing for ethanol was greater on signalled trials (CS+) than on unsignalled trials (Blank +), indicating that ethanol's reinforcing efficacy was altered by CS+. Ethanol self-administration was significantly correlated with the anticipatory increase in body temperature on CS+ trials (Pearson r=+0.77). When ethanol was removed, leaving sucrose alone as the reinforcer, the signal's effect on barpressing was eliminated. This finding suggests the signal's effect depended on ethanol's pharmacological properties. In general, these data are consistent with theories that attribute the signal's effect to conditioned changes in motivation to obtain ethanol or to an interaction between the conditioned response and ethanol's unconditioned effects. The specific pattern of results appears to support hypotheses linking ethanol's thermal and motivational effects. According to this view, conditioned hyperthermia produced tolerance to an aversive ethanol effect (hypothermia) that normally contributes to termination of an ethanol drinking bout, thereby allowing a longer period of self-administration on signalled trials.