Abstract Introduction Up to 75% of chronic pain patients report difficulty maintaining sleep, frequent nocturnal awakenings, and non-restorative sleep. In murine models of neuropathic pain, we similarly observe more brief arousals during NREM sleep than in pain-free controls. Despite the clinical relevance of pain-induced sleep disruption, nociceptive processing during sleep remains poorly understood. Here, we quantified pain-evoked arousability across sleep states (NREM and REM) and sleep conditions: spontaneous sleep, high sleep pressure (recovery sleep after acute sleep deprivation), and fragmented sleep induced by neuropathic pain. This design tested whether (i) increased sleep pressure and specific pre-stimulus EEG features modulate the probability of pain-evoked awakenings, and (ii) a pre-existing pain condition further increases vulnerability to nociceptive awakenings. Methods Adult mice expressing channelrhodopsin-2 selectively in Nav1.8+ neurons (C and Aδ fibers) were implanted with EEG/EMG electrodes and habituated to recording conditions. During continuous EEG/EMG monitoring, calibrated optogenetic stimuli were delivered to the plantar hindpaw during NREM or REM sleep under three conditions: spontaneous sleep, recovery sleep (after acute sleep deprivation), and fragmented sleep in a neuropathic pain model. Arousals were scored offline using EEG/EMG and time-locked video/observer logs to classify each stimulus as triggering an “awakening” or a “sleep-through” (maintained sleep). Pre-stimulus EEG power in conventional frequency bands was quantified. Results Pain-evoked awakenings were strongly state-dependent, with the highest probability during NREM sleep (~90 %) and the lowest during REM sleep ( 5%). High sleep pressure and deeper NREM sleep moderately increased the likelihood of maintaining sleep through nociceptive simulations. When nociceptive stimuli did not trigger an awakening, the preceding NREM sleep showed higher EEG power in the delta (0.5-4.5 Hz) and sigma (10-15 Hz; spindles) frequency ranges, suggesting that ongoing slow-waves and spindles can modulate the probability of pain-evoked arousability. Conclusion Optogenetic activation of peripheral nociceptors reveals that pain-evoked awakenings are gated by both global sleep state and cortical EEG dynamics. Identifying EEG signatures associated with resilience or vulnerability to pain-related awakenings may guide the development of sleep-based biomarkers and interventions to protect sleep in patients with chronic pain conditions. Support (if any) Blaustein Pain Research Fund (CA)
Alexandre et al. (Fri,) studied this question.