title: Plasticity of circadian behavior and the suprachiasmatic nucleus following exposure to non-24-hour light cycles.
abstract: Period aftereffects are a form of behavioral plasticity in which the free-running period of circadian behavior undergoes experience-dependent changes. It is unclear whether this plasticity is age dependent and whether the changes in behavioral period relate to changes in the SCN or the retina, 2 known circadian pacemakers in mammals. To determine whether these changes vary with age, Per1-luc transgenic mice (in which the luciferase gene is driven by the Period1 promoter) of different ages were exposed to short (10 h light: 10 h dark, T20) or long (14 h light: 14 h dark, T28) light cycles (T cycles). Recordings of running-wheel activity in constant darkness (DD) revealed that the intrinsic periods of T20 mice were significantly shorter than of T28 mice at all ages. Aftereffects following the shorter light cycle were significantly smaller in mice older than 3 months, corresponding with a decreased ability to entrain to T20. Age did not diminish entrainment or aftereffects in the 28-h light schedule. The behavioral period of pups born in DD depended on the T cycle experienced in utero, showing maternal transference of aftereffects. Recordings of Per1-luc activity from the isolated SCN in vitro revealed that the SCN of young mice expressed aftereffects, but the periods of behavior and SCN were negatively correlated. Enucleation in DD had no effect on behavioral aftereffects, indicating the eyes are not required for aftereffects expression. These data show that circadian aftereffects are an age-dependent form of plasticity mediated by stable changes in the SCN and, importantly, extra-SCN tissues.
authors.affiliation: Department of Biology, Washington University, St. Louis, MO 63130-4899, USA. sjaton@artsci.wustl.edu
authors.forename: Sara J
authors.initials: SJ
authors.lastname: Aton
authors.forename: Gene D
authors.initials: GD
authors.lastname: Block
authors.forename: Hajime
authors.initials: H
authors.lastname: Tei
authors.forename: Shin
authors.initials: S
authors.lastname: Yamazaki
authors.forename: Erik D
authors.initials: ED
authors.lastname: Herzog
mesh_terms: D000367:Age Factors; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000502:physiology*; D015353:Eye Enucleation; D008027:Light; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056950:Period Circadian Proteins; D017440:Photoperiod; D011897:Random Allocation; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013493:Suprachiasmatic Nucleus / Q000502:physiology*
chemical_list: D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; C539023:Per1 protein, mouse; D056950:Period Circadian Proteins; D011993:Recombinant Fusion Proteins