Role of Preoptic Area γ-Aminobutyric Acid–mediated Neurons in Distinctly Regulating Sleep and Rousability during Dexmedetomidine Sedation in Mice

Background: γ-Aminobutyric acid–mediated (GABAergic) neurons in the preoptic area (POA) play a crucial role in sleep regulation, with distinct subpopulations promoting wakefulness and sleep. Dexmedetomidine has the unique property of inducing arousable sedation, but the underlying mechanisms remain incompletely understood. In this study, the authors propose that POA-derived GABAergic neurons regulate natural sleep and wakefulness states through different projections and act similarly for dexmedetomidine-induced sedation and arousability. Methods: In this study, 99 male and 56 female Gad2-IRES-Cre mice and 10 male C57BL/6J mice (n = 165) were used. The power density in the electroencephalography/electromyography bands was used to assess the depth of dexmedetomidine-induced sedation and to determine the sleep–wakefulness states. A fiber photometry/patch clamp was used to detect changes in the excitability of GABAergic neurons projecting from the POA to the ventral tegmental area (VTA; GABA POA-VTA neurons) and to the lateral hypothalamus (LH; GABA POA-LH neurons). Chemogenetics was used to modulate the excitability of the GABA POA-VTA and GABA POA-LH neurons. Viral tracing was used to map the functional connectivity between POA-derived GABAergic neurons and their targets in the VTA and LH. Results: According to the electroencephalography, electromyography, and fiber photometry recordings, GABA POA-VTA neurons showed elevated activity during natural wakefulness or 40 μg/kg dexmedetomidine–induced sedation. Chemogenetic activation of GABA POA-VTA neurons increased natural wakefulness and reduced dexmedetomidine-induced sedation. The GABA POA-VTA and GABA POA-LH neurons played opposing roles in natural sleep and dexmedetomidine-induced sedation. Retrograde tracing revealed a minimal overlap between these two neuronal subpopulations. Orthodromic tracing demonstrated that GABA POA-VTA neurons preferentially innervated VTA-derived GABAergic neurons, whereas GABA POA-LH neurons mainly projected to LH orexin neurons. Conclusions: In addition to mediating the sedative versus arousal effects of dexmedetomidine, two distinct subpopulations of GABAergic neurons in the POA are also responsible for promoting natural sleep and wakefulness, respectively.