Functional Suppression of CLOCK Activity in Ventromedial Hypothalamic Prodynorphin Neurons Alters Locomotor Activity and Rapid Eye Movement Sleep

<b>Background/Objectives</b>: The circadian regulator, circadian locomotor output cycles kaput (CLOCK), is well-established in maintaining sleep-wake rhythms, yet its cell-type-specific functions in sleep regulation remain largely unexplored. While ventromedial hypothalamic (VMH) prodynorphin (PDYN)-expressing (VMH^PDYN+) neurons are known to modulate homeostatic and motivational processes, their potential role in circadian sleep regulation has not been investigated. <b>Methods</b>: To address this, we developed mice with PDYN neuron-specific functional suppression of CLOCK activity (mClkΔ19) by interfering with their internal clock through Adeno-Associated Virus (AAV)-mediated overexpression of dominant-negative CLOCKΔ19 in PDYN-Cre mice. <b>Results</b>: We found that mClkΔ19 mice exhibited reduced locomotor activity during the dark phase, earlier activity peaks, and impaired rhythmicity of rapid eye movement (REM) and non-REM (NREM) sleep. Sleep analysis in mClkΔ19 mice showed selective reductions and fragmentation of light-phase REM sleep, more frequent sleep-wake transitions, and shorter REM cycles during the dark phase, indicating disrupted REM sleep timing. EEG spectral analysis in mClkΔ19 mice revealed decreased gamma activity during REM sleep in the light phase and an increase in delta activity coupled with decreased gamma during wakefulness in the dark phase. <b>Conclusions</b>: These findings suggest that the CLOCK activity in VMH^PDYN+ neurons is vital for circadian accuracy, REM sleep stability, and brain oscillations during sleep-wake cycles.