title: Altered Electroencephalographic Activity Associated with Changes in the Sleep-Wakefulness Cycle of C57BL/6J Mice in Response to a Photoperiod Shortening.
abstract: OBJECTIVE
  Under natural conditions diurnal rhythms of biological processes of the organism are synchronized with each other and to the environmental changes by means of the circadian system. Disturbances of the latter affect hormonal levels, sleep-wakefulness cycle and cognitive performance. To study mechanisms of such perturbations animal models subjected to artificial photoperiods are often used. The goal of current study was to understand the effects of circadian rhythm disruption, caused by a short light-dark cycle regime, on activity of the cerebral cortex in rodents.
  
  
  METHODS
  We used electroencephalogram to assess the distribution of vigilance states, perform spectral analysis, and estimate the homeostatic sleep drive. In addition, we analyzed spontaneous locomotion of C57BL/6J mice under symmetric, 22-, 21-, and 20-h-long light-dark cycles using video recording and tracking methods.
  
  
  CONCLUSIONS
  We found that shortening of photoperiod caused a significant increase of slow wave activity during non-rapid eye movement sleep suggesting an elevation of sleep pressure under such conditions. While the rhythm of spontaneous locomotion was completely entrained by all light-dark cycles tested, periodic changes in the power of the θ- and γ-frequency ranges during wakefulness gradually disappeared under 22- and 21-h-long light-dark cycles. This was associated with a significant increase in the θ-γ phase-amplitude coupling during wakefulness. Our results thus provide deeper understanding of the mechanisms underlying the impairment of learning and memory retention, which is associated with disturbed circadian regulation.
authors.affiliation: Department of Anatomy, Faculty of Medicine, Neuroscience Center, University of Helsinki Helsinki, Finland.
authors.forename: Stanislav V
authors.initials: SV
authors.lastname: Rozov
authors.affiliation: Department of Physiology, Faculty of Medicine, University of Helsinki Helsinki, Finland.
authors.forename: Janneke C
authors.initials: JC
authors.lastname: Zant
authors.affiliation: A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland Kuopio, Finland.
authors.forename: Kestutis
authors.initials: K
authors.lastname: Gurevicius
authors.affiliation: Department of Physiology, Faculty of Medicine, University of Helsinki Helsinki, Finland.
authors.forename: Tarja
authors.initials: T
authors.lastname: Porkka-Heiskanen
authors.affiliation: Department of Anatomy, Faculty of Medicine, Neuroscience Center, University of Helsinki Helsinki, Finland.
authors.forename: Pertti
authors.initials: P
authors.lastname: Panula
keywords: circadian; desynchrony; entrainment; sleep; wakefulness