Effects of choline and acetylcholine chloride upon peripheral nerve fibers

Abstract

SEVEN FIGURESAcetylcholine, a substance which even when employed in minute concentrations, exerts a powerful excitatory action at certain synaptic junctions, is not known to have any action upon the nerve fibers themselves.According to observations made by Riesser ( '21), acetylcholine chloride at a concentration of 0.001% has no excitatory effect upon nerve, and if any, has only a slight excitatory action on muscle; but acetylcholine chloride elicits muscular contraction when it is applied to that region of the muscle where the neuromuscular junctions are located. Evidence was offered by Riesser to show that the excitatory effect of acetylcholine takes place at the neuromuscular junction. At present it is well-known that minute amounts of acetylcholine may elicit muscular contraction when the drug is delivered directly t o the zone of the neuromuscular junction by intra-arterial injection (cf. literature in Brown, '37).With regard to the difference between the action of acetycholine upon ganglionic synapses and that exerted upon preganglionic fibers, an experiment performed by Bronk and his co-workers (Bronk, '39) is particularly valuable. When acetylcholine is added at a concentration of 0.01% to the fluid with which a sympathetic ganglion is being perfused, a powerful discharge of postganglionic impulses results, whereas acetylcholine at even five times that concentration (0.05%) is not capable of initiating impulses in the preganglionic fibers. I n this report the effect of large concentrations of acetylcholine chloride upon the sciatic neme of the bullfrog is described and compared with the effect produced by choline chloride, magnesium chloride, eserine sulphate, and glucose.An analysis of the effect of the test substances has been made: (1) by measuring the demarcation potentials between a 10-mm. long segment of the nerve in contact with a large volume of the test solution, 85