Behavioral animal models in alcohol abuse research

Alcohol Health & Research World,  Fall, 1990  by Kathleen A. Grant

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Alcohol affects behavior in myriad ways. Even in the same individual, alcohol can have vastly different effects depending on an individual's current setting and past experiences with alcohol. Alcohol can increase or decrease aggression; it can stimulate or suppress eating; or it can accelerate physical and verbal activity or depress behavior. The effects of alcohol can be so desirable that an individual repeatedly acts to obtain it or so unpleasant that an individual habitually avoids it. Given this spectrum of effects, the answers to the basic questions, "Why do humans drink alcohol?" and "When is occasional use likely to develop into abuse?" are extremely complicated.

To answer these questions, scientists have developed experimental animal models in which the animals' behavior appears analogous to human behavior with respect to alcohol. Researchers design animal models to study the actions of alcohol on particular behaviors in isolation, free from interference from other sources. Researchers do not use these models to cause laboratory animals to become alcoholic; rather, they design them to focus on the variables affecting only a single behavior that may contribute significantly to excessive drinking or alcoholism.

In other words, animal models do not duplicate human conditions because researchers eliminate many of the factors that otherwise would interacts to influence behavior. Researchers isolate and study the effects of alcohol on only a few factors at a time. Although researchers find it difficult to control for many important variables, including genetic background, nutritional status, and history of exposure to alcohol when the subject is human, animal models allow almost total control over these variables, enabling researchers to determine the contribution of separate variables to the outcome of an experiment. This information then allows researchers to predict the ways in which a particular factor under study might affect human alcohol consumption.

The determinants of alcohol abuse are many, and this article describes only a few of the major factors. Discussion of the physiological and neurochemical correlates of alcohol abuse and of the toxic damage that results from heavy alcohol intake will be limited. However, comprehensive reviews on these topics are available (for example, see Eriksson et al. 1980).

THE REINFORCING EFFECTS OF

ALCOHOL

"Why do people drink alcohol?" In behavioral terms, alcohol is reinforcing if, when an individual consumes it, it is likely that drinking or the behaviors used to obtain alcohol will occur again. Thus, the positive effects of alcohol (it can feel good) can reinforce drinking alcohol, or the effects of alcohol that alleviate negative states (it can relieve anxiety) can reinforce its consumption.

With this in mind, the question can be rephrased: "Under what circumstances is alcohol reinforcing?" This question emphasizes observable behavioral events such as drinking, and it removes the emphasis from subjective factors such as an individual's self-report of why he or she consumes alcohol. Researchers then can observe the circumstances that are likely to lead to repetition of behavior that results in the presentation of alcohol.

Determining the Positive Reinforcing

Effects of Alcohol in Animal Models

The best procedure for studying the positive reinforcing effects of alcohol in animals is to allow the animals to consume alcohol voluntarily--to self-administer alcohol. However, many of the common species of laboratory animals (and, in fact, most humans) do not readily consume alcohol voluntarily following their initial sampling of an alcoholic beverage (Samson 1987). To overcome initial aversion to the effects of alcohol, researchers use various procedures to induce drinking in laboratory animals, for example, by masking the taste of the alcohol with a sweet solution (Samson 1987).

To introduce animals to the effects of alcohol without having to overcome the initial aversion to its taste, researchers use intravenous administration, in which alcohol is injected directly into the bloodstream, or intragastric administration, in which alcohol is fed through a tube directly into the animal's stomach. However, even these routes of administration can require an initial period during which the animal becomes accustomed to the effects of alcohol and gradually accepts them (Winger and Woods 1973). After several sessions, the animals begin to ingest (self-administer) alcohol solutions readily. When an animal drinks alcohol solely for its effects, alcohol has become reinforcing for the animal.

Researchers are interested in measuring the behavior an animal must perform to acquire alcohol, such as licking a tube, pressing a lever, or moving to a specific location within a chamber. After an animal performs or repeats the behavior, the researcher can administer alcohol either by direct infusion, as described above, or by presenting a dipper containing alcohol. The actions of alcohol, once it enters an animal's bloodstream and brain, maintain the behaviors the animal must perform to obtain and consume alcohol.