Sleep-Wake Cycle in Young and Older Mice.

Sara Soltani,Julie Carrier,Igor Timofeev,Sylvain Chauvette,Josée Seigneur,Jonathan Dubé,Jean-Marc Lina,Olga Bukhtiyarova

doi:10.3389/fnsys.2019.00051

Abstract

Sleep plays a key role in multiple cognitive functions and sleep pattern changes with aging. Human studies revealed that aging decreases sleep efficiency and reduces the total sleep time, the time spent in slow-wave sleep (SWS), and the delta power (1–4 Hz) during sleep; however, some studies of sleep and aging in mice reported opposing results. The aim of our work is to estimate how features of sleep–wake state in mice during aging could correspond to age-dependent changes observed in human. In this study, we investigated the sleep/wake cycle in young (3 months old) and older (12 months old) C57BL/6 mice using local-field potentials (LFPs). We found that older adult mice sleep more than young ones but only during the dark phase of sleep-wake cycle. Sleep fragmentation and sleep during the active phase (dark phase of cycle), homologous to naps, were higher in older mice. Older mice show a higher delta power in frontal cortex, which was accompanied with similar trend for age differences in slow wave density. We also investigated regional specificity of sleep–wake electrographic activities and found that globally posterior regions of the cortex show more rapid eye movement (REM) sleep whereas somatosensory cortex displays more often SWS patterns. Our results indicate that the effects of aging on the sleep–wake activities in mice occur mainly during the dark phase and the electrode location strongly influence the state detection. Despite some differences in sleep–wake cycle during aging between human and mice, some features of mice sleep share similarity with human sleep during aging.

Highlights

Older mice showed larger local-field potentials (LFPs) delta power in the frontal cortex compared to young mice, which can be explained by a tendency for an increase in slow wave density
We found an increase with aging in the delta power and a trend for an increased slow wave density in frontal cortex, but stable delta power in the posterior part of somatosensory cortex
We found that electrodes implanted in frontal cortex would identify more of wake, in motor and somatosensory cortex more slow-wave sleep (SWS) and in visual and retrosplenial cortex more rapid eye movement (REM) sleep (Figure 6)

Summary

Introduction

Middle-age subjects show a reduced sleep efficiency, duration, slowwave density, and a reduced amplitude of slow waves compared to young adults (Carrier et al, 2011; Mander et al, 2017). A study compared EEG recordings above the somatosensory cortex of 6 months old to 18–24 months old C57BL/6JOlaHsd male mice and found an increase in the sleep amount in the older group as well as an increase in the delta range power (Panagiotou et al, 2017). Another group found that C57BL/6 mice show only a non-significant trend for an increase in their daily amount of non-REM sleep from 3 to

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