Altered Electroencephalographic Activity Associated with Changes in the Sleep-Wakefulness Cycle of C57BL/6J Mice in Response to a Photoperiod Shortening.

Stanislav V. Rozov,Kestutis Gurevicius,Janneke C. Zant,Pertti Panula,Tarja Porkka-Heiskanen

doi:10.3389/fnbeh.2016.00168

Abstract

Aim: 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.Results and 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.

Highlights

The ability to adjust to periodic environmental changes is one of the key properties of the circadian system
The shortening of the circadian period was accompanied by a gradual linear increase in the average distance moved during the daytime (p = 0.004, Linear mixed effect model (LMM) followed by likelihood ratio test (LRT), Figure 1C, left panel) and a slight increase (p < 0.001, LMM followed by LRT) followed by a linear decrease at night (p = 0.008, LMM followed by LRT, Figure 1C, right panel)
The changes were highly dependent on the interaction between the phase of the light–dark cycle and the period length (p < 0.001, LMM followed by LRT)

Summary

Introduction

The ability to adjust to periodic environmental changes is one of the key properties of the circadian system. To characterize changes of the circadian regulation under such conditions studies on animals, subjected to light-dark cycles beyond the entrainment range of the circadian clock, have been performed These experimental protocols non-invasively disrupt normal functioning of the circadian system, which appears as an altered electrophysiological activity of the neurons in the SCN (Houben et al, 2014), expression of core clock genes Per and Bmal in this brain region (de la Iglesia et al, 2004) and production of melatonin, which serves as a hormonal arm of the oscillator (Schwartz et al, 2009). Several studies on humans (Wyatt et al, 1999) and rodents (Laakso et al, 1995; Cambras et al, 2007; Lee et al, 2009) utilizing symmetric 10/10 or 11/11 light-dark (LD) schedules, reported desynchronization between the locomotor activity and NREMsleep that primarily followed LD cycle and REM-sleep and body temperature that were adhered to the internal circadian rhythm

Objectives

Methods

Results

Conclusion