Enkephalinergic Neurons in Barrington's Nucleus Gate Sex-Specific Control of Micturition.

Lower urinary tract (LUT) control is a vital physiological function governed by a complex interplay between neural circuits and muscle activity. This regulation depends on brainstem circuits, with Barrington's nucleus (Bar) acting as a central hub. Here, we construct a transcriptional atlas of Bar, uncovering its neuronal diversity and extensively characterize a distinct excitatory population expressing proenkephalin (Bar-Penk). Using in vivo calcium imaging and optogenetics, we demonstrate that Bar-Penk neurons selectively activate during voiding and specifically facilitate external urethral sphincter (EUS) relaxation. Chemogenetic activation of these neurons elicits an aberrant micturition phenotype in male but not female mice, whereas conditional ablation impairs voluntary scent-marking behavior. Moreover, anatomical tracing reveals that Bar-Penk neurons project to spinal regions critical for LUT control and receive convergent input from areas involved in visceromotor regulation and behavioral state processing. These findings position Bar-Penk as a specialized brainstem population that integrates internal states and environmental cues to orchestrate context-dependent urinary behaviors in a sex-specific manner.