Rapid eye movement (REM) sleep disturbances are prevalent in various psychiatric disorders. However, the neural circuits that regulate REM sleep remain poorly understood. Here, we found that in male mice, optogenetic activation of rostromedial tegmental nucleus (RMTg) GABAergic neurons immediately converted REM sleep to arousal and then initiated non-REM (NREM) sleep. Conversely, laser-mediated inactivation completely converted NREM to REM sleep and prolonged REM sleep duration. The activity of RMTg GABAergic neurons increased to a high discharge level at the termination of REM sleep. RMTg GABAergic neurons directly converted REM sleep to wakefulness and NREM sleep via inhibitory projections to the laterodorsal tegmentum (LDT) and lateral hypothalamus (LH), respectively. Furthermore, LDT glutamatergic neurons were responsible for the REM sleep-wake transitions following photostimulation of the RMTgGABA-LDT circuit. Thus, RMTg GABAergic neurons are essential for suppressing the induction and maintenance of REM sleep.

The parasubthalamic nucleus (PSTN) is considered to be involved in motivation, feeding and hunting, all of which are highly depending on wakefulness. However, the roles and underlying neural circuits of the PSTN in wakefulness remain unclear. Neurons expressing calretinin (CR) account for the majority of PSTN neurons. In this study in male mice, fiber photometry recordings showed that the activity of PSTNCR neurons increased at the transitions from non-rapid eye movement (non-REM, NREM) sleep to either wakefulness or REM sleep, as well as exploratory behavior. Chemogenetic and optogenetic experiments demonstrated that PSTNCR neurons were necessary for initiating and/or maintaining arousal associated with exploration. Photoactivation of projections of PSTNCR neurons revealed that they regulated exploration-related wakefulness by innervating the ventral tegmental area. Collectively, our findings indicate that PSTNCR circuitry is essential for the induction and maintenance of the awake state associated with exploration.

The lateral periaqueductal gray (LPAG) is essential for coordinating active and passive defensive behaviors which rely on heightened arousal, but its impact on sleep–wake regulation remains unknown. Here, by using targeted recombination in active populations transgenic mouse tool along with neuroanatomical approaches, we first show that two different populations of glutamatergic neurons are activated during wakefulness and rapid eye movement (REM) sleep in the LPAG. Fiber photometry showed that most LPAG vesicular glutamate transporter 2 (Vglut2) neurons are preferentially active during wakefulness. Chemogenetic and optogenetic activation of LPAGVglut2 neurons strongly enhanced arousal associated with immobility. The wakefulness- and immobility-promoting effects of LPAGVglut2 neurons are mediated by their projections to the locus coeruleus and ventral gigantocellular reticular nucleus, as supported by optogenetic manipulations. In contrast, chemogenetic inhibition of LPAGVglut2 neurons reduced REM sleep and increased non-REM sleep. Most LPAG neurons activated during REM sleep hypersomnia and showed descending projections to the sublaterodorsal tegmental nucleus. These findings revealed that two different LPAGVglut2 populations of neurons and circuits induce wakefulness associated with immobility and REM sleep.