Abstract
In this chapter we discuss the vexed question as to whether prejunctional cholinoceptors exist at the neuromuscular junction, and if so, what physiological function they might serve. There is some controversy in the literature about several aspects of the subject that are best illustrated by posing a series of questions, as follows: 1. Does acetylcholine exert one or more actions on motor nerve endings, and are these mediated by nicotinic or muscarinic receptors, or both? 2. If acetylcholine can act on the motor nerve endings, has its action (or actions) at this site any physiological relevance in relation to the transmission process? 3. Do neuromuscular blocking drugs (e.g. tubocurarine, gallamine, decametho-nium, snake α-toxins) act on motor nerve endings as well as on postjunctional cholinoceptors? 4. 4. If they do act prejunctionally, is their action mediated through choHnoceptor sites in the nerve endings, or is it a quite separate action that is independent of their known ability to interact with nicotinic cholinoceptors? 5. 5. Do anticholinesterase drugs (e.g. neostigmine, diisopropyl fluorophosphate) act on motor nerve endings as well as on junctional Cholinesterase, and if they do so act, is their action direct or mediated by preserved transmitter acetylcholine?
Published Version
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