Effects of ganglionic blocking agents on the neuromuscular junction

Abstract

Effects of ganglionic blocking agents on neuromuscular transmission and on responses of nicotinic agents have been studied using the baby chick biventer cervicis nerve muscle preparation. Responses of nicotinic agents such as nicotine, tetramethylammonium, dimethylphenylpiperazinium and carbachol were markedly inhibited by 10 mg % of hexamethonium (C 6) and 100 mg % of tetraethylammonium (TEA) and almost completely abolished by 100 mg % of C 6 and 1 g% of TEA. However, responses induced by ACh were not significantly affected by these ganglionic blocking agents, indicating that nicotinic agents were blocked by these ganglionic blocking agents at a site other than the ACh receptor, probably at the motor nerve endings. Neuromuscular transmission was also blocked by C 6 and TEA without affecting ACh responses suggesting that C 6 and TEA might block the uptake of choline bynerve across the membrane and thus inhibit ACh synthesis and thereby block neuromuscular transmission. Initial facilitation and concomitant contraction of the biventer cervicis muscle preceded neuromuscular blockade induced by TEA indicating that part of the TEA effect might be due to the release of endogenous ACh.