Sympathetic Postganglionic Cholinergic Fibres

Abstract

When the postganglionic fibres to the nictitating membrane are stimulated in a cat treated with reserpine, the membrane contracts. The contraction is increased after the injection of eserine and is abolished with atropine. Thus the fibres stimulated appear to be cholinergic. When the splenic nerve is stimulated in a cat treated with reserpine there is similar evidence of the presence of cholinergic fibres ; the spleen dilates, the dilatation is greater in the presence of eserine and is abolished by atropine. The hypogastric nerves when stimulated cause inhibition of the uterus of the virgin cat. When the cat is treated with reserpine, stimulation then causes contraction which is increased in the presence of eserine and abolished by atropine. There is also evidence of cholinergic fibres in the postganglionic supply to the vessels of the rabbit's ear. From this and other evidence it is suggested that a form of adrenergic mechanism may exist such that cholinergic fibres in the postganglionic sympathetic supply liberate acetylcholine ; this in turn liberates noradrenaline from a store around the sympathetic nerve ending.Many effects produced in the body by stimulation of sympathetic nerves are also produced by acetylcholine (after atropine) and by nicotine acting peripherally. Vasoconstriction in the vessels of the isolated and perfused rabbit ear is an example. Since these effects of acetylcholine and of nicotine disappear (a) after treatment of the animal with reserpine and (b) after degeneration of the sympathetic nerves, it seemed that the effwts might actually be mediated through some part of the sympathetic mechanism. Cholinergic fibres have been shown to occur in various sympathetic nerves, the first demonstration of them having been made by Euler and Gaddum (1931).We have therefore carried out an investigation to see if fibres liberating acetylcholine were present in postganglionic sympathetic nerves generally, and have studied the supply to the nictitating membrane, the spleen, the uterus of the nonpregnant cat and the perfused rabbit ear. Bacq and Fredericq (1935) had already given evidence for the presence of cholinergic fibres in the nictitating membrane. We thought that if sympathetic nerves in general contained cholinergic fibres. the acetylcholine liberated might then have the same effect as injected acetylcholine or nicotine. METHODS Our method has been to study the effect of stimulating postganglionic sympathetic fibres in cats or rabbits treated with reserpine. This treatment reduces or removes the store of noradrenaline present around the sympathetic nerve endings and makes it easier to see effects which might be produced by release of acetylcholine.Reserpine was dissolved in a 20"; solution of ascorbic acid, and usually a 1 ' % solution was prepared which was injected into the peritoneal cavity on two successive days. The animal was used for the experiment on the third day. The amount injected was 1.5 mg./kg. on each day. The animals were kept in a warm room at a temperature of 27".For observatio...