Reflex Increases in Heart Rate Elicited by Stimulation of Afferent Cardiac Sympathetic Nerve Fibers in the Cat

A reflex tachycardia elicited by electrical stimulation of afferent cardiac sympathetic nerve fibers was observed in anesthetized, vagotomized cats. Tachyordia was obtained by stimulating the cut central end of the left inferior cardiac nerve in closed-chest, spontaneously breathing cats and in open-chest, artificially ventilated cats and by stimulating the cut central end of the pericoronary nerve, thus restricting the stimulus to afferent sympathetic fibers with cardiac endirgs. Reflex tachycardia was also obtained in spinal cats. In general, the magnitude of the reflex response was inversely related to the control heart rate. The afferent pathway for the reflex was contained in the first four left thoracic rami communicantes, and the efferent limb depended on the integrity of the right stellate ganglion. These results demonstrate that cardiocardiac spinal neural circuits can also mediate reflex increases in heart rate.