Mammalian sleep consists of two states: rapid-eye-movement (REM) sleep and non-REM (NREM) sleep. REM sleep is characterized by rapid eye movements, loss of muscle tone, and hippocampal theta waves. Recent studies have indicated that reduction of REM sleep is associated with an increased risk of dementia and all-cause mortality. While enhancing REM sleep may offer health benefits, the mechanisms and physiological roles of REM sleep remain incompletely understood. Previous studies have shown that the dorsal pons plays a crucial role in the regulation of REM sleep. However, little is known about the subtype of neurons that positively regulate REM sleep. To tackle this, we employed a genetic approach and found a novel genetically marked subtype of neurons that may regulate REM sleep in mice. Cell-type specific ablation of these neurons resulted in a decrease in both NREM sleep and REM sleep, and chemogenetic activation of medullary projecting neurons increased REM sleep. However, the activity of these neurons during a natural sleep/wake cycle is unknown. To address this, we performed single-unit recording using a glass pipette electrode combined with the Cre-loxP system and the opto-tagging method to accomplish cell-type-specific recording. Of the 60 neurons recorded, nearly half of them exhibited maximal firing rates during REM sleep. In addition, we performed cell type and projection-specific recording and found that, within this subpopulation, those that project to the medulla exhibited maximal firing rates during REM sleep. These results strongly support that these neurons contribute to regulating REM sleep.