OBSERVATIONS ON DRUG-INDUCED ACTIVATION OF CHOLINOCEPTIVE SITES IN A SYMPATHETIC GANGLION

¹ Department of Pharmacology, Michigan State University, East Lansing, Michigan

The mode of administration played an important role in determining the pharmacologic characteristics of the ganglionic responses evoked by tetramethylammonium (TMA) and aoetylchuohine (ACh). The poslganglionic discharge evoked by a single injection of TMA was abolished by hiexamethionium (C₆) and was unaltered by atropine. In contrast, the distcharge evoked during the infusion of TMA was blocked by either C₆ or atropine. The infusion rates of TMA employed did not alter transmission. The data suggest that infusion of TMA initiated an interaction between the C₆-sensitive and atropimie-sensitive excitatory ganghionic cholinoceptive sites. It is proposed that the spread of depolarization from the C₆-sensitive site markedly enhanced a weak muscarinic stimulating action of TMA. Thus, the postganglionic discharge evoked during the infusion of TMA appeared to emanate mainly from the atropine-sensitive site. In contrast to the C₆-sensitive firing evoked in unconditioned ganglia by a single injection of ACh, constant rate infusion of the compound usually elicited a discharge which was blocked by atropine and not by C₆. This disparity between the ability of single injections and infusions of ACh and TMA to evoke C₆-sensitive and alropine-sensitive discharges is discussed.