Afferent aortic nerve fibers with their pathways in cardiac sympathetic nerves

The effect of mechanical and chemical stimulation on activity of afferent aortic nerve fibers with pathways in the cardiac sympathetic nerves has been examined. Action potentials were derived from the second or third thoracic communicating ramus of the left side of anesthetized dogs. Thirty myelinated and 19 unmyelinated fibers responded to tapping the ascending aorta, aortic arch, and descending aorta. Both groups of fibers also responded to a rise as well as to a fall in aortic pressure. Spontaneous discharge of myelinated fibers was related to aortic pressure pulse whereas that of unmyelinated fibers was related to respiration. Asphyxia caused excitation of unmyelinated fibers but not of myelinated fibers. Both groups of fibers responded to topical application of lactic acid. Mechanical and chemical stimulation of the aorta after vagotomy caused a rise in systemic blood pressure and extension of the limbs. The results indicate the existence of afferent aortic fibers in the cardiac sympathetic nerves that cause circulatory and somatic responses.