Pharmacology and Nerve-Endings

A brief account is given of the scientific career of Walter Ernest Dixon, and of the importance of his work and his influence for the development of Pharmacology in England. It is suggested that the Memorial Lecture may appropriately deal with some matter of new interest, from one of the fields of research in which Dixon himself was active. Special mention is made of his work with Brodie on the physiology and pharmacology of the bronchioles and the pulmonary blood-vessels, as probably showing the beginning of Dixon's interest in the actions of the alkaloids and organic bases which reproduce the effects of autonomic nerves. An account is given of Dixon's early interest in the suggestion, first made by Elliott, that autonomic nerves transmit their effects by releasing, at their endings, specific substances, which reproduce their actions; and of his attempt to obtain experimental support for this conception. After the War it was established by the experiments of O. Loewi; and it is now generally recognized that parasympathetic effects are so transmitted by release of acetylcholine, sympathetic effects by that of a substance related to adrenaline. Very recent evidence indicates that acetylcholine, by virtue of its other (“nicotine-like”) action, also acts as transmitter of activity at synapses in autonomic ganglia, and from motor nerve to voluntary muscle. The terms “cholinergic” and “adrenergic” have been introduced to describe nerve-fibres which transmit their actions by the release at their endings of acetylcholine, and of a substance related to adrenaline, respectively. It is shown that Langley and Anderson's evidence, long available, as to the kinds of peripheral efferent fibres which can replace one another in regeneration, can be summarized by the statement, that cholinergic can replace cholinergic fibres, and that adrenergic can replace adrenergic fibres; but that fibres of different chemical function cannot replace one another. The bearing of this new evidence on conceptions of the mode of action of “neuromimetic” drugs is discussed. The pharmacological problem can now be more clearly defined, and Dixon's participation in further attempts at its solution will be sadly missed.