Vagal volume receptors in the heart compensate for blood loss and posture change

Cranial nerves densely innervate the heart and vasculature, with sensory neurons reporting on blood pressure, respiratory gases, and tissue damage¹. The roles of arterial baroreceptors in systemic physiology are well appreciated², but the functions of vagal cardiac mechanoreceptors have been more difficult to parse, in part due to the closed-loop structure of the cardiovascular system. Here, we use genetic tools for isolated study of vagal mechanoreceptors in the heart, finding that they are acutely sensitive to circulating blood volume and play key roles in compensating for decreased filling of the heart that occurs in an upright posture and during hemorrhage. Vagal PIEZO2 neurons form characteristic end-net endings in the heart and display blood volume-dependent responses with every heartbeat that are time-locked to atrial and ventricular systole. Vagal PIEZO2 knockout eliminates heartbeat-coupled nerve activity, and compromises carotid blood pressure when mice on a tilt-table are rotated to an upright position. Vagal PIEZO2 knockout mice also display a lethal failure to sustain blood pressure during trauma-induced blood loss. Together, these findings demonstrate an essential function for vagal cardiac mechanoreceptors in sustaining the constancy of blood circulation.