Behavioral animal models in alcohol abuse research

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

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The amounts of alcohol that maintain alcohol-seeking behavior apparently occur within a narrow dose range in most laboratory animals (Meisch 1977). Usually the doses required to maintain alcohol-seeking behavior result in blood concentrations of approximately 0.05 percent to 0.1 percent of the animal's total blood volume (0.1 percent is the level that legally determines intoxication in humans in most of the United States). Animals consistently will drink this amount of alcohol under many different conditions.

For example, studies reviewed in Meisch 1977 have shown that if the volume of alcohol available is altered, the animal will adjust the number of drinks it takes to maintain an even alcohol intake. Similarly, if the concentration of alcohol is altered, then the animal will adjust the volume of alcohol it consumes to maintain an even intake. Finally, if before the start of a drinking session, researchers give an animal one-half the dose of alcohol it normally consumes, it will decrease its alcohol intake during the session by one-half. These results illustrate that, in an animal used to drinking alcohol, total doses of alcohol that result in blood concentration levels between 0.5 percent and 0.1 percent are reinforcing and that the animal will adjust its behavior to attain them.

Alcohol and Negative States

As already mentioned, alcohol may be reinforcing because it is perceived as decreasing pain or other negative states, such as anxiety. The reduction of negative states as an inducement to continue alcohol consumption is known as negative reinforcement. The end result of reinforcement, whether positive or negative, is the same--continued drinking of alcohol. Animal models are used to study negative as well as positive reinforces for alcohol consumption and alcohol-seeking behavior.

Researchers studying animal models of anxiety equate a particular behavioral response with an underlying state of anxiety. A description of a conflict procedure illustrates this approach: A thirsty animal receives an electric shock when it drinks water (not alcohol) from a particular spout. Following a few pairings of drinking and shock, the animal will avoid drinking water from that spout. Researchers presume that the animal is anxious about the possibility of receiving another shock, even though it still is thirsty. If, however, the animal first is administered alcohol before returning to the place where it received a shock and given another opportunity to drink from that spout, it no longer is reluctant to do so (Cappell 1975; Cappell and Greeley 1987).

In other studies (reviewed in Cappell and Greeley 1987), researchers place an animal in an environment in which it previously had experienced a stressful event, such as a shock. The animal then is given an opportunity to drink alcohol, and researchers compare the amount of alcohol it consumes in the stress-associated environment with the amount of alcohol it consumes in an environment with which stress has never been associated. If the animal increases its drinking in an environment associated with stress, the increase may be attributed to the animal's perception that alcohol reduces anxiety. This perception can be negatively reinforcing, that is, it may further the probability that the animal will drink in the future.