Regulation of REM Sleep by Inhibitory Neurons in the Dorsomedial Medulla

Mammalian sleep can be subdivided into two distinct brain states, rapid eye movement sleep (REMs) and non-REM sleep (NREMs). Each state is characterized by distinct brain rhythms ranging from millisecond to minute-long (infraslow) oscillations. The mechanisms controlling transitions between sleep states and how they are synchronized with infraslow brain rhythms remain poorly understood. Here, 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. Calcium imaging using fiber photometry demonstrated that dmM GABAergic neurons are strongly activated during REMs. During NREMs, their activity fluctuated in close synchrony with infraslow oscillations in the sigma power of the electroencephalogram (EEG). Together, these findings functionally and anatomically delineate a specific population of medullary neurons that powerfully control REMs. The slow oscillations in the activity of the dmM neurons may serve as a physiological link coordinating transitions from NREMs to REMs with infraslow brain rhythms.