Animal Models of Alcohol's Motivational Effects

Alcohol's positive and negative motivational effects are believed to be important influences on alcohol-seeking behavior and, therefore, key factors among the many and varied causes of alcohol abuse and dependence. Alcohol's positive effects, such as enhanced mood, and negative effects, such as hangover, are considered important factors in motivating drinkers to increase or decrease their drinking. Scientists have developed a variety of animal behavioral models to study alcohol's motivational effects. These models include "self-administration models," in which the animal controls the exposure to alcohol, and "conditioning models," in which the researcher controls the animal's exposure to alcohol. Such models have been used to study the influence of genetic differences on sensitivity to alcohol's positive and negative motivational effects, the brain mechanisms underlying alcohol's motivational effects, as well as relapse and craving. The causes of excessive alcohol use and alcoholism are complex, reflecting the interaction of a wide range of genetic, environmental, sociocultural, and experiential factors. Among these factors, alcohol's positive and negative motivational effects often stand out in theoretical analyses of alcohol-seeking behavior. Researchers believe, for example, that alcohol's positive effects on mood may motivate a person to drink more, and that likewise, alcohol's negative effects, such as hangover, may motivate a person to drink less. These effects are considered important factors in determining whether people who drink will continue to consume alcohol and increase their intake of alcohol over time (Tabakoff and Hoffman 1988). KEY WORDS: animal model; AOD (alcohol or other drug) -seeking behavior; motiv ation; self administration of drugs; operant conditioning; learning; memory; place conditioning; taste conditioning Positive motivational effects produced by alcohol can include increases in pleasurable states (e.g., elation and euphoria) as well as the alleviation of unpleasant states such as those produced by stress, anxiety, or physical dependence and withdrawal. Negative motivational effects produced by alcohol may include increases in unpleasant states (e.g., dysphoria, illness, hangover) or reductions in pleasurable states (e.g., reduced elation). Presumably, individual differences in sensitivity to such motivational effects can either facilitate or inhibit the development of excessive drinking patterns characteristic of alcohol abuse and alcoholism. Given the theoretical significance placed on alcohol's motivational effects, scientists have developed a variety of animal behavioral models to assess those effects. Although many different animal species have been examined, most studies have used monkeys or rodents (e.g., rats and mice). Many of the initial efforts in this area were heavily criticized for failing to meet the formal criteria proposed for "animal models of alcoholism" (e.g., Lester and Freed 1973; Cicero 1979). For example, few animal models have shown sustained voluntary intake of alcohol at levels that produce a withdrawal syndrome when the alcohol is removed. Most investigators in the field, however, no longer view animal models as attempts to create "alcoholism." Rather, these models are now used primarily to characterize alcohol's motivational effects, with the hope that this knowledge will shed light on the roles these motivational effects play in developing and maintaining excessive drinking in humans. Researchers also use these models to study neurobiological and genetic mechanisms underlying alcohol's motivational effects and to develop pharmacological and behavioral interventions to alter those effects. The purpose of this article is to offer a brief overview of the animal behavioral models currently used to study alcohol's motivational effects. This overview will focus on models that directly measure seeking or avoidance of alcohol or alcohol-paired stimuli (e. …