Role of Acetylcholine and Vitamin B₁ in Nervous Excitation

Abstract

AT the cut end of a peripheral nerve acetylcholine¹ and vitamin B₁² are set free and diffuse into the bathing fluid at rest and during excitation. The amount set free during excitation is considerably greater than during rest. The production of these and maybe other substances at the cut end of a stimulated nerve can be made visible with the aid of the Schlieren method of Toepler³. If short periods of stimulation are interchanged with periods of rest, the substances diffusing out are seen as little outbursts of 'clouds' near the cut end of the nerve, showing that it is mainly the excited state which leads to the production of these substances. Their appearance might have been due to a decrease in permeability during excitation and not to an actual formation. This possibility is ruled out by the fact that freezing stimulated nerves with liquid air, making use of the principle of the Doppler effect in order to accumulate the excitation waves, leads to an actual increase of these substances in extracts obtained from the frozen and minced nerve. In the excited nerve (sciatic of Hungarian Esculenta) an increase of 0.1 µgm. acetylcholine per gm. nerve has been measured with great regularity in fifty independent experiments, with an average error of ± 0.0l µgm. The ratio of acetylcholine content in stimulated and unstimulated nerve is 1.6⁴. The extracts of stimulated nerves show at the same time a great increase in vitamin B₁ content. This increase has been demonstrated with six independent methods (increase of the response of a leech-preparation to acetylcholine⁵, a new polarographic method⁶, Flagellatæ-test², Phycomyces-test⁷, bradycardia-test of the rat⁸, thiochrome-reaction⁹) and amounts to 2 µgm. per gram nerve.