The Circadian Timing System in Ethanol Consumption and Dependence

The use of alcohol is an important part of the daily lives of many individuals that may be experienced as a single nightly drink with a meal or a debilitating pattern of intoxication. The circadian timing system imposes a daily temporal order throughout the brain and body. Ethanol, with its complex and broad pharmacology, can thereby alter circadian physiology at multiple levels of organization. Here, we review data from animal models demonstrating that (a) perturbations of the circadian timing system are often, but not necessarily, reflected in altered drinking behaviors or ethanol response; (b) alcohol can act to alter the circadian entrainment and pacemaking functions of the suprachiasmatic nuclei; and (c) the temporal patterning of alcohol exposure and withdrawal in a circadian context can influence processes related to addiction development, particularly increased voluntary alcohol consumption and development of physical dependence as reflected in the physiological withdrawal reaction. New data are presented to show that the withdrawal reaction elicited after long-duration alcohol vapor sessions is significantly modulated according to the time of day that it is initiated. Further application of chronobiological principles to alcohol research should enhance mechanistic understanding and suggest potential therapeutic approaches.