Chronobiological Regulation of Alcohol Intake
Hiller-Sturmhofel, Susanne, Kulkosky, Paul, Alcohol Research & Health
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 animals' consumption patterns throughout the day, however, such an approach is not adequate, particularly if such measurements are to be conducted over several days. Moreover, several bottle changes per day would require waking up the animals periodically, which by itself could influence their drinking behavior and thereby confound the results. Therefore, scientists have developed various types of apparatus that continuously measure fluid consumption and record that information either on a paper printout or, more recently, on a computer. For example, Eriksson (1972) designed a device that measures the fluid level in a laboratory drinking bottle using an electrical probe that is immersed in the bottle and which records specific changes in signal voltage as the fluid level in the bottle decreases. Other investigators have used specially designed cages and drinking bottles that are connected to an electrical circuit and which generate a signal each ti me the animal licks at the spout of the bottle to receive fluid (e.g., Freund 1970; Dole et al. 1983). Especially with the use of computers to automatically collect, store, and analyze the data, the most current devices can provide investigators with an accurate picture of the times and amounts of fluid consumed by each animal under various environmental conditions. As a result, techniques exist today that allow simultaneous microstructural analysis of the animals' alcohol, fluid, and food intake (Boyle et al. 1997; Reidelberger et al. 1996). These newer techniques are much more precise and accurate than the earlier procedures previously described and often reveal differences as well as similarities in how and why rats consume alcohol in comparison with humans (Dole et al. 1985; Sinclair 1980).
Some researchers have noticed that the general pattern of food and fluid consumption in rodents resembles a 24-hour sinusoidal curve, with peak levels of consumption around the middle of the dark phase and the lowest (i.e., trough) levels around the middle of the light phase. Based on this observation, investigators can generate a curve that reasonably reflects the animals' food and fluid (including alcohol) intake based on just a few measurements conducted at evenly spaced intervals …
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Publication information: Article title: Chronobiological Regulation of Alcohol Intake. Contributors: Hiller-Sturmhofel, Susanne - Author, Kulkosky, Paul - Author. Journal title: Alcohol Research & Health. Volume: 25. Issue: 2 Publication date: Spring 2001. Page number: 141. © 2008 U.S. Government Printing Office. COPYRIGHT 2001 Gale Group.
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