State dependence of pontine astrocyte calcium dynamics across sleep-wake cycles

Astrocyte calcium signals are region-specific and state-dependent across the sleep-wake cycle. However, their role in sleep regulation remains poorly understood. Since the pons is critical for sleep, especially rapid eye movement (REM) sleep regulation, we investigate the dynamics of pontine astrocyte calcium signals and their role in REM sleep induction in mice. We monitored pontine astrocyte calcium signals by expressing GCaMP6f under the control of gfaABC1D promoter and implanted optic fiber into the sublaterodorsal tegmental nucleus (SLD). Also, we simultaneously acquired cortical electroencephalograms (EEG) and electromyograms (EMG) in freely behaving conditions. As previously reported, we confirmed that pontine astrocytes exhibit state-dependent calcium dynamics: spectrally rich signals during wakefulness and non-REM (NREM) sleep with a consistent reduction during REM sleep. To explore the temporal relationship between pontine astrocyte population activity and cortical states, we examined how the activity state (up- and down-states at an infra-slow (<0.1 Hz) frequency) of pontine astrocyte populations correlate with cortical EEG signals in the delta (1-4 Hz) and theta (6-8 Hz) bands.Our preliminary results suggest a state-dependent functional coupling between cortical states and pontine astrocyte ensembles. Since we also found that chemogenetic activation of pontine astrocytes can reduce NREM-to-REM transitions, we explore a potential mechanism. This presentation will also discuss how pontine astrocyte calcium signals are modulated by mesopontine neuronal activity across the sleep-wake cycle.