Effects of denervation on the sensitivity of the superior cervical ganglion of the cat to acetylcholine and McN-A-343

Abstract

Supersensitivity of the denervated superior cervical ganglion of the cat to acetylcholine (Ach) has been reported by workers who measured contractions of the nictitating membrane, and denied by others who measured postganglionic action potentials as an index of ganglion activity. The present experiments were performed to find out the reason for this discrepancy. The increased responses of nictitating membranes to intra-arterial administration of Ach to denervated ganglia were found to be due to increased sensitivity of membranes to the adrenergic neurotransmitter rather than to an increase in the sensitivity of the ganglia. McN-A-343, a muscarinic agent, produced a greater maximal contraction of the membrane when injected to denervated than when injected to control ganglia. These results suggest that denervation causes an increase in the number and (or) sensitivity of muscarinic receptors in ganglia. Hexamethonium antagonized Ach less effectively on denervated than on control ganglia. The effect of Ach on denervated ganglia was blocked by hexamethonium plus atropine, which suggests that Ach acts both on nicotinic and muscarinic receptors in denervated ganglia. Atropine but not hexamethonium blocked the effect of McN-A-343 on both control and denervated ganglia.