Proceedings of The Physiological Society

Sleep Sleep and Circadian Rhythms (London, UK) (2018) Proc Physiol Soc 42, C10

Poster Communications

Effects of selective silencing of layer 5 pyramidal neurons on sleep-wake regulation and cortical network dynamics

L. Krone1,2, T. Yamagata2, A. Hoerder-Suabedissen1, Z. Molnár1, V. Vyazovskiy1,2

1. Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, United Kingdom. 2. Sleep and Circadian Neuroscience Institute, University of Oxford, Oxford, United Kingdom.

Sleep and wakefulness are controlled by neuronal clusters in brainstem, hypothalamus, and basal forebrain in the mammalian brain (1). Although local cortical regulation of sleep depth and sleep slow waves has been shown (2,3), it remains unclear whether cortex contributes to global sleep-wake regulation. Cortical layer 5 pyramidal neurons are a key population in the generation and propagation of cortical slow oscillations (4,5). Slow waves are an electroencephalographic (EEG) hallmark of non-rapid eye movement (NREM) sleep and their spectral power (slow wave activity, SWA, 0.5 - 4 Hz) is a precise marker of sleep pressure. In this study, we probe the role of layer 5 pyramidal neurons in sleep-wake regulation and cortical network dynamics in mice. We performed EEG and 16-channel laminar cortical recordings in a transgenic mouse model, in which a subpopulation (~15-30 %) of pyramidal cells in layer 5 is functionally silenced by removal of the t-SNARE protein SNAP25 (Rbp4-Cre;Ai14;Snap25fl/fl). Male adult mice (10-17 weeks, 5 homozygous, 4 Cre-negative controls) were single-housed on a 12h/12 h light/dark cycle (light onset at 9 am). Sleep deprivation (SD) was performed on one day by exposure to novel objects for 6 hours starting at light onset. In undisturbed 24-hour recordings, layer 5 silenced animals presented anincreased total amount of wakefulness (13.28 hrs, SEM 0.55 hrs) compared to controls (10.52 hrs, SEM 0.36 hrs). In addition, the maximum duration of individual wake episodes was longer in layer 5 silenced animals (282.1 min, SEM 84.0 min) compared to controls (89.6 min, SEM 17.5 min). Following six hours of sleep deprivation, the increase of slow wave activity during NREM sleep relative to baseline was diminished in layer 5 silenced animals (134.9%, SEM: 5.7%) compared to controls (190.1%, SEM: 6.9%). The laminar profile of cortical activity revealed recurrent spike-wave patterns in transgenic animals, which did not occur in controls. Our preliminary results indicate altered sleep-wake regulation in transgenic mice with a silenced subpopulation of layer 5 pyramidal neurons. Layer 5 silenced mice exhibit extended wakefulness, a greater capacity to stay awake, and a diminished homeostatic response to sleep deprivation. Furthermore, the fine orchestration of cortical activity appears disturbed. We tentatively interpret this data as first evidence that layer 5 pyramidal neurons contribute to the global regulation of sleep and wakefulness. This specific cortical cell population might represent a core element in a homeostatic circuit, which tracks the cortical need for sleep and translates it into a sleep signal.

Where applicable, experiments conform with Society ethical requirements