Synaptic and neuro-muscular transmission

Abstract

The centre of interest in the field of synaptic and neuro-muscular transmission has been for some time occupied by the two conflicting hypotheses of chemical and electrical mediation. Moreover this conflict is not restricted to transmission to any one type of effector,for it now appears certain that, with the exception of diffuse chemical mediation from postganglionic endings, the same hypothesis must cover all transmissions. In their discussion on skeletal muscleDale, Feldberg andVogt (1936) have thus stated the problem of the relation between diffuse chemical mediation from postganglionic endings and the more specialized transmissions: “The question which here concerns us is whether in voluntary striated muscle, specialized for the quick contraction of individual fibres in response to nerve impulses, and normally at rest in their absence, this more primitive, chemical method of transmission has been superseded by an entirely different one, in which the chemico-physical disturbance constituting the nerve impulse passes... on to the muscle fibre; or whether, on the other hand, the required specialization has been effected by concentrating the release and the action of the chemical stimulant at the point of immediate contact of the nerve ending with the muscle fibre.” From the developmental aspect there is something to be said for both answers, for on the one hand the chemical localization would involve a less fundamental change, and on the other hand with the development of a specialized intracellular propagation by all-or-nothing impulses an associated development of a specialized intercellular propagation might also be expected. At present the chemical and electrical hypotheses must both be regarded as on probation. This uncertainity must be emphasized, as the apparently convincing evidence which has been adduced in support of either hypothesis has led to premature decisions, just as in the case of the biochemistry of muscular contraction. Approached from the pharmacological aspect, the evidence for chemical mediation seems indisputable, and equally convincing is the electrical hypothesis from the electrical point of view; hence coordination of pharmacological and electrical investigation is desirable. Further investigation should also be attempted in relation to the detailed study of the changes which nerve impulses set up in the various effectors, and functional regeneration after cross-union experiments also requires re-investigation from the histological, physiological and pharmacological aspects. An eventual solution may not be easily and quickly attained, for the minute and rapid changes responsible for the transmission can only be indirectly investigated, and theoretical arguments from experimental evidence are hampered by our inadequate knowledge of cell physiology and pharmacology, especially in relation to the behaviour of specialized regions of cells.