title: Drugs of abuse can entrain circadian rhythms.
abstract: Circadian rhythms prepare organisms for predictable events in the 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.
authors.affiliation: Department of Neurology, Indiana University School of Medicine, 975 W. Walnut St., IB 455, Indianapolis, IN 46202, USA. akosobud@iupui.edu
authors.forename: Ann E K
authors.initials: AE
authors.lastname: Kosobud
authors.forename: Andrea G
authors.initials: AG
authors.lastname: Gillman
authors.forename: Joseph K
authors.initials: JK
authors.lastname: Leffel
authors.forename: Norman C
authors.initials: NC
authors.lastname: Pecoraro
authors.forename: G V
authors.initials: GV
authors.lastname: Rebec
authors.forename: William
authors.initials: W
authors.lastname: Timberlake
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D002940:Circadian Rhythm / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects; D006801:Humans; D010805:Physical Conditioning, Animal / Q000502:physiology; D019966:Substance-Related Disorders / Q000503:physiopathology*