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Volume 7, Pages 203-212
Mini-Review Article

Drugs of Abuse Can Entrain Circadian Rhythms

1Department of Neurology, Indiana University School of Medicine, 975 W. Walnut St., IB 455, Indianapolis, IN 46202, USA
2Department of Psychological and Brain Sciences, Indiana University, 1101 E. 10th St., Bloomington, IN 47405, USA
3Department of Physiology, University of California, 13 Parnassus Ave., San Francisco, CA 94143-0444, USA

Received 5 July 2007; Revised 6 August 2007; Accepted 7 August 2007

Academic Editors: D. Shurtleff and S. Ferre

Copyright © 2007 Ann Kosobud et al.


Circadian rhythms prepare organisms for predictable events during the Earth's 24-h day. These rhythms are entrained by a variety of stimuli. Light is the most ubiquitous and best known zeitgeber, but a number of others have been identified, including food, social cues, locomotor activity, and, most recently drugs of abuse. Given the diversity of zeitgebers, it is probably not surprising that genes capable of clock functions are located throughout almost all organs and tissues. Recent evidence suggests that drugs of abuse can directly entrain some circadian rhythms. We have report here that entrainment by drugs of abuse is independent of the suprachiasmatic nucleus and the light/dark cycle, is not dependent on direct locomotor stimulation, and is shared by a variety of classes of drugs of abuse. We suggest that drug-entrained rhythms reflect variations in underlying neurophysiological states. This could be the basis for known daily variations in drug metabolism, tolerance, and sensitivity to drug reward. These rhythms could also take the form of daily periods of increased motivation to seek and take drugs, and thus contribute to abuse, addiction and relapse.