Behavioral animal models in alcohol abuse research

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

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These studies demonstrate clearly that tolerance is not merely a matter of an animal having been exposed to alcohol. When the administration of alcohol is associated with environmental events, the environment and the effects of the alcohol interact to influence the speed with which and the extent to which the animal develops tolerance (Goudie and Demellweek 1986). How tolerance to the effects of alcohol influences alcohol intake is not clear, and this is a matter of debate and ongoing research.

CONDITIONED EFFECTS OF

ALCOHOL

The animal studies described above illustrate that animals can associate the effects of alcohol with environmental stimuli, such as a place or a distinctive light. Some interesting studies have demonstrated that if researchers expose an animal to environmental stimuli that it associates with alcohol or other drug ingestion, the animal may increase the behaviors is performs to obtain more of the alcohol or other drug (Stewart et al. 1984). It is as if the environmental stimuli can trigger the animal's cravings for alcohol. Researchers have concluded that if an animal has many associations between drinking alcohol and events or items in its surroundings, the chances that the animal will crave alcohol increase (reviewed in Stewart et al. 1984).

EXPERIMENTAL MODELS OF

ALCOHOL DEPENDENCE

After prolonged exposure to large amounts of alcohol, animals can develop not only tolerance to the effects of alcohol and conditioned responses to stimuli associated with its consumption, but also dependence on the alcohol itself. An alcohol-dependent animal can exhibit both physiological and behavioral symptoms. The physiological symptoms of alcohol dependence--tremors and increased excitability of the central nervous system--appear after alcohol has been metabolized and eliminated from the animal's body and is not replaced. Increased central nervous system excitability is manifested as tremors and sometimes convulsions, and it usually follows a long period of heavy alcohol consumption. Symptoms such as heightened central nervous system excitability contrast with the common signs of intoxication that follow an episode of drinking (for example, slowed reaction times and impaired motor coordination), and they follow a characteristic time course (Majchrowicz 1975).

When an animal undergoes withdrawal from alcohol, its central nervous system reacts more intensely to--is more sensitive to--the normal signals it receives, both environmental and internal. Heightened sensitivity develops as the animal's nervous system attempts to adapt to the sudden lack of alcohol. During the period when the animal is consuming large quantities of alcohol, its nervous system adapts to, or becomes tolerant of, the sedating effects of the alcohol. When alcohol and its sedating effects suddenly are not available to the animal, the responses of its central nervous system to normal stimuli are exaggerated. At times, these responses include convulsions. Thus, the animal's nervous system adapts to the presence of alcohol and then malfunctions in its absence.