Incentive Salience and High (HiS) or Low (LoS) Saccharin Preference: A Model for Drug Abuse Vulnerability

Abstract

Human drug addicts show a higher preference for sweetened dietary substances compared to non-addicts. This relationship between sweet preference and addiction vulnerability has been modeled with rats selectively bred for high (HiS) and low (LoS) saccharin intake. One question central to research on addiction pertains to the mechanism driving these phenotypic behavioral differences. Incentive salience is a phenomenon in which contextual stimuli associated with rewarding events begin to function as conditioned stimuli and elicit approach and contact behaviors, and drugs of abuse are thought to accelerate this process. Incentive salience has been modeled with animals with a procedure in which the extension of a lever acts as a cue that is immediately followed by the presentation of a noncontingent food pellet. A percentage of rats exhibit the development of incentive salience by displaying sign-tracking (ST) behavior in which they approach and bite the lever, while other rats show goal-tracking (GT) behavior in which they approach the food delivery receptacle during the lever extension. Importantly, the ST rats show greater drug-seeking compared to GT rats. Thus, in this experiment, we examined ST vs. GT behavior in HiS and LoS male and female rats to determine whether rats selectively bred to prefer sweet substances also show elevated incentive salience by demonstrating sign tracking. Results indicated no differences between ST or GT behaviors in HiS vs. LoS rats; however, females showed more ST than males, and they also show higher rates of drug-seeking than males, suggesting that sex may mediate the incentive salience process and may contribute to our understanding of sex differences in addiction vulnerability.