Regulation of REM sleep by inhibitory neurons in the dorsomedial medulla

The two major stages of mammalian sleep—rapid eye movement sleep (REMs) and non-REM sleep (NREMs)—are characterized by distinct brain rhythms ranging from millisecond to minute-long (infraslow) oscillations. The mechanisms controlling transitions between sleep stages and how they are synchronized with infraslow rhythms remain poorly understood. Using opto- and chemogenetic manipulation in mice, we show that GABAergic neurons in the dorsomedial medulla (dmM) promote the initiation and maintenance of REMs, in part through their projections to the dorsal and median raphe nuclei. Fiber photometry revealed that their activity is strongly increased during REMs and fluctuates during NREMs in close synchrony with infraslow oscillations in the sleep spindle band of the electroencephalogram. The phase of this rhythm influenced the latency and probability with which dmM activation induced REMs. Thus, dmM inhibitory neurons strongly promote REMs, and their slow activity fluctuations may coordinate the timing of REMs episodes with infraslow brain rhythms. •GABAergic neurons in the dorsomedial medulla (dmM) strongly promote REM sleep•Activating dmM neurons projecting to the dorsal/median raphe induces REM sleep•The activity of dmM neurons fluctuates during NREM sleep in sync with EEG sigma power•The sigma power oscillation influences the timing of REM sleep induction by the dmM Stucynski et al. show that GABAergic neurons in the dorsomedial medulla (dmM) promote REM sleep, in part through projections to the dorsal/median raphe. During NREM sleep, these neurons fluctuate in close synchrony with an infraslow oscillation in the EEG sigma power. This infraslow rhythm influences the timing of REM sleep induction by the dmM.