Activation of afferent cardiac sympathetic nerve fibers of the cat by pain producing substances and by noxious heat

Abstract

Afferent discharges of 64 single units were recorded from the left cardiac sympathetic nerve of anesthetized cats. Mechano-sensitive terminals of the afferent fibers were localized in the extrapulmonary part of the pulmonary artery, left atrium, left ventricle and left pericardium, as determined by direct mechanical probing of the heart after death of the animals. Conduction velocity of the fibers ranged from 2.5 to 14.6 m/s. Excitation of these Adelta-fibers with mechanically excitable endings was produced by intravenous injections of acetylcholine, 5-hydroxytryptamine, bradykinin, histamine and veratridine, and/or by topical application of these agents to the receptor region. Noxious heat to the mechanically excitable field in the wall of the pulmonary artery and the left ventricle also activated their afferent fibers. These observations provide evidence for a certain number of afferent units in the cardiac sympathetic nerve with polymodal sensitivity. These afferent fibers can provide the spinal cord with information not only on mechanical changes in cardiac events, but also changes in the chemical environment of the cardiac nerve ending, possibly produced by myocardial ischemia.