What Are Recent Insights Into Pontomedullary Circuits Controlling in REM Sleep?

Recent studies have identified neurochemically defined neuronal groups in the pons and medulla that have a critical role in initiation, maintenance, and manifestations of REM sleep (REM-on neurons). The sublaterodorsal tegmental nucleus (SLD) in rodents (subcoeruleus nucleus in humans) contains a group of glutamatergic neurons that express corticotrophin-releasing hormone‑binding protein (Crhbp + neurons) that initiate REM sleep and elicit REM sleep atonia by projections to inhibitory neurons of the ventromedial medulla projecting to spinal motor neurons. A reciprocal glutamatergic excitatory loop between these SLD Crhbp + neurons and neurons in the dorsomedial medulla expressing nitric oxide synthase 1 (Nos1+ neurons) form a core circuit that initiates and maintains REM sleep. Other neurochemically defined neuronal groups in the dorsomedial medulla trigger rapid eye movements and other phasic phenomena during REM sleep. Both the ventromedial medulla and the dorsomedial medulla contain GABAergic neurons that promote REM sleep by inhibiting REM-off neurons.