Effects of Catecholamines in the Cat Superior Cervical Ganglion and Their Postulated Rôle as Physiological Modulators of Ganglionic Transmission

Abstract

Publisher Summary This chapter describes the effects of noradrenaline (NA) and isoproterenol on transmission in the superior cervical ganglion of the cat. The superior cervical ganglion receives its preganglionic input by the cervical sympathetic trunk, which can be easily prepared for stimulation. NA depresses ganglionic transmission by an action on presynaptic structures by reducing the release of acetylcholine (ACh). Isoproterenol produces facilitation by the depolarization of the ganglion. The inhibition by NA and facilitation by isoproterenol can be blocked by the α-adrenergic receptor blocker dihydroergotamine and the β-adrenergic receptor blocker propranolol, respectively. The effects of catecholamines are mediated by two distinct pharmacological receptors. Experiments designed to detect an effect of NA released within the ganglion by presynaptic volleys gave negative results. The inhibitory effect on the ganglionic transmission of NA reaching the ganglion by its blood supply and the presence of considerable amounts of this amine in the ganglion led to speculations about its involvement in normal ganglionic transmission.