Academic journal article Alcohol Research

Alcohol, Antidepressants, and Circadian Rhythms

Academic journal article Alcohol Research

Alcohol, Antidepressants, and Circadian Rhythms

Article excerpt

Human and Animal Models

Alcohol consumption (both acute and chronic) and alcohol withdrawal have a variety of chronobiological effects in humans and other animals. These effects are widespread, altering the circadian rhythms of numerous physiological, endocrine, and behavioral functions. Thus, some of alcohol's negative health consequences may be related to a disruption of normal physiological timing. Most studies of alcohol's chronobiological effects have been conducted under natural conditions in which environmental stimuli, such as regular cycles of light and darkness, act to coordinate circadian rhythms with the environment and with each other. However, such studies cannot distinguish between effects occurring directly on the circadian pacemaker and those occurring "downstream" from the pacemaker on the physiological control systems. Studies using animals have enabled researchers to begin to examine the effects of alcohol on circadian rhythms under so-called free-running conditions in experimental isolation from potential environmental synchronizers. These studies have provided preliminary evidence that alcohol's chronobiological effects are indeed the result of direct influences on the circadian pacemaker itself. Furthermore, the effects of alcohol on animal circadian rhythms appear similar to the effects seen during administration of antidepressant drugs. Taken together with evidence that the chronobiological effects of alcohol withdrawal in human alcoholics are reminiscent of those described in depressed patients, these observations suggest that alcohol may produce antidepressantlike effects on the circadian pacemaker. One theory suggests that the effects of alcohol on the circadian pacemaker are mediated in part by alterations in serotonin, an important chemical involved in cellular communication within the circadian system. However, other neurochemical systems also are likely to be involved. KEY WORDS: circadian rhythm; antidepressants; AOD (alcohol or other drug) use pattern; physiological AODE (effects of AOD use, abuse, and dependence); hypothalamus; CNS (central nervous system) nuclei; brain pathway; serotonin; human study; animal study

As evidenced by the articles assembled for this issue of Alcohol Research & Health, at least three separate lines of evidence suggest a link between alcohol ingestion and the regulation of the body's daily biological, or circadian, rhythms regulating sleep and activity, body temperature, hormone secretions, and essentially all other important physiological and behavioral processes.

First, circadian rhythms modulate several behavioral and physiological responses to alcohol in both humans and experimental animals. Circadian modulation of a drug's effect is not specific to alcohol, however, because circadian variations in drug effectiveness also are seen for numerous other substances, including other psychoactive drugs.

Second, the propensity for voluntary alcohol intake is influenced by the circadian system in both humans and animals. People and other animals with access to alcohol in studies essentially tend to drink at specific times of the day or night. For example, rats and mice exhibit maximal levels of voluntary alcohol consumption during the night phase of their circadian cycle. Because the animals' daily pattern of alcohol intake closely resembles their normal daily patterns of food and water intake, the circadian modulation of alcohol intake may not reflect a specific influence on alcohol-seeking behavior, but may instead reflect an influence on active behavior in general.

Third, the normal circadian patterns of a variety of behavioral and physiological parameters (e.g., sleep and activity, body temperature, hormone secretions) are disrupted by alcohol administration, ingestion, and/or withdrawal. Such effects are the focus of this article, which examines alcohol's effects on circadian rhythmicity in people and animals and explores some possible underlying neuropharmacological mechanisms. …

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