State-dependent brainstem ensemble dynamics and their interactions with hippocampus across sleep states

Abstract

The brainstem plays a crucial role in sleep-wake regulation. However, the ensemble dynamics underlying sleep regulation remain poorly understood. Here, we show slow, state-predictive brainstem ensemble dynamics and state-dependent interactions between the brainstem and the hippocampus in mice. On a timescale of seconds to minutes, brainstem populations can predict pupil dilation and vigilance states and exhibit longer prediction power than hippocampal CA1 neurons. On a timescale of sub-seconds, pontine waves (P-waves) are accompanied by synchronous firing of brainstem neurons during both rapid eye movement (REM) and non-REM (NREM) sleep. Crucially, P-waves functionally interact with CA1 activity in a state-dependent manner: during NREM sleep, hippocampal sharp wave-ripples (SWRs) precede P-waves. On the other hand, P-waves during REM sleep are phase-locked with ongoing theta oscillations and are followed by burst firing of CA1 neurons. This state-dependent global coordination between the brainstem and hippocampus implicates distinct functional roles of sleep.

Simultaneous Electrophysiology and Fiber Photometry in Freely Behaving Mice

“…We observed frequent calcium transients during REM sleep as well as phasic, large fluctuations of pEEGs. These signals were qualitatively similar to those which were separately observed in our previous study (Tsunematsu et al, 2020).…”

“…We recently reported P-waves in mice (Tsunematsu et al, 2020). Because mesopontine cholinergic neurons have been implicated in P-wave genesis (Callaway et al, 1987;Datta, 1997), we examined whether P-waves co-appear with calcium transients in mesopontine cholinergic neurons during REM sleep.…”

“…The surgical procedures have been described previously (Tsunematsu et al, 2020). Briefly, mice were anesthetized with isoflurane (5% for induction, 1-2% for maintenance) and placed in a stereotaxic apparatus (SR-5M-HT, Narishige).…”

“…Vigilance states were visually scored offline as described elsewhere (Tsunematsu et al, 2020). Wakefulness, NREM sleep, or REM sleep was determined over a 4-s resolution, based on cortical EEG and EMG signals using a custom-made MATLAB Graphical User Interface.…”

“…In the present study, we develop a versatile custom-made fiber photometry system with the capability to integrate in vivo electrophysiological recording in freely behaving mice. To validate our system, we focus on pontine waves (P-waves), which were reported in mice recently (Tsunematsu et al, 2020). Because mesopontine cholinergic neurons have been implicated in the induction of P-waves (Callaway et al, 1987;Datta, 1997), we monitor calcium transients from GCaMP6s-expressing mesopontine cholinergic neurons along with detecting P-waves electrophysiologically.…”