Academic journal article Alcohol Research

Chronobiological Regulation of Alcohol Intake

Academic journal article Alcohol Research

Chronobiological Regulation of Alcohol Intake

Article excerpt

Like other physiological functions, food intake and metabolism (including alcohol consumption) in humans and animal models may be regulated by circadian rhythm. For example, many studies of rodents have found that alcohol consumption in these nocturnal animals peaks during their active dark period. This alcohol consumption pattern can be influenced, however, by experimental manipulation. One factor that has been proposed to play a role in regulating circadian alcohol consumption pattern is the hormone melatonin, which is produced by the pineal gland. Research also indicates that the effects of lighting conditions on the alcohol consumption of animal models may be influenced by the differences among the strains of the laboratory animals used, variations in the type and administration schedule of the animals' alcohol-containing diet, disruptions of the normal circadian rhythm, concurrent use of other drugs, and properties of the light. KEY WORDS: circadian rhythm; biological regulation; light; time of day; AOD (alcohol or other drug) use pattern; pineal gland; melatonin; cholecystokinin; animal model; laboratory rat

The activity patterns and body functions of humans (like those of other animals) are, at least in part, regulated by general environmental influences, such as temperature and lighting conditions. In particular, the daily light-dark cycle (also called the diurnal cycle) has shaped the activity patterns of most animals over millions of years of evolution. Thus, humans generally are active during the daylight and rest during darkness (although modern technology, such as the invention of electrical light, has vastly modified those natural activity patterns). Conversely, rodents are primarily nocturnal animals. These general activity patterns influence numerous other behaviors, including food consumption and metabolism. Accordingly, alcohol consumption patterns in humans and laboratory animals may be affected by the circadian) (i.e., lasting approximately 24 hours) rhythm and the daily light-dark cycle.

This article first describes briefly how researchers assess the alcohol consumption patterns of laboratory animals across the diurnal cycle. It then reviews the influence of daily lighting conditions on the alcohol consumption of rodents and explores the biological mechanisms that may underlie these influences. Finally, the article presents some of the factors that influence the relationship between lighting conditions and alcohol consumption. This discussion briefly describes the implications of these studies for alcohol consumption patterns in humans, particularly in people whose regular circadian rhythm is frequently disrupted (e.g., shift workers or people traveling across different time zones). Many of the topics discussed in this article generated considerable interest primarily in the 1970s and 1980s but, despite their potential relevance to human alcohol consumption patterns, have not yet been thoroughly pursued. As a result, at least part of the literature reviewed in this article is relatively old, although this does not negate its validity.

ASSESSING DIURNAL DRINKING PATTERNS

To determine the influence of lighting conditions and diurnal drinking patterns of laboratory animals, researchers must regularly monitor the animals' water (and/or alcohol) consumption. Some studies in this area have focused on the animals' overall fluid consumption per day under various lighting conditions (e.g., normal light-dark cycles, continuous darkness, or continuous light). For these experiments, the animals have constant access to drinking bottles filled with a specific amount of water and/or an alcohol solution, and their fluid consumption is measured one or more times per day.

When the goal of the experiment is to determine in detail the anima& consumption patterns throughout the day, however, such an approach is not adequate, particularly if such measurements are to be conducted over several days. …

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