An anatomical and day–night atlas links cochlear immunity to adjacent bone marrow

The cochlea lies within marrow-bearing bone. How this neighbouring marrow relates to cochlear immunity and daily physiology remains poorly resolved. We profiled 160,643 cells from mouse cochlea and adjacent temporal-bone marrow at six times of day, with rhythm inference calibrated for one pooled sample per time. Three-dimensional confocal reconstruction mapped vascular connections between marrow and cochlea and localized neutrophils along this interface. Neutrophils also occupied healthy cochlear fluids. Parabiosis findings were consistent with a local marrow contribution to cochlear immunity. Structural cochlear cells maintained synchronized, light-entrained clocks. Cochlear neutrophil programmes aligned with circulating neutrophils and opposed those in marrow, with independent flow cytometry supporting daily changes in immune composition and CXCR4. A shared night-associated heat-shock programme was attenuated after noise in an independent cohort. These anatomical and temporal data provide a reference for testing local marrow supply and the origins of cochlear immune rhythms.