Transmission and block in autonomic ganglia / by W.D.M. Paton.

  • Paton, William D. M.
Date:
[1954?]
Catalogue details

Licence: In copyright

Credit: Transmission and block in autonomic ganglia / by W.D.M. Paton. Source: Wellcome Collection.

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    times difficult to show this on other ganglia. Recent work using ganglia removed in toto either from the turtle or from the rabbit (12, 20) and studied thus deprived of natural circulation, has revealed that in the curarized ganglion pre-ganglionic stimulation can under some circumstances produce a potential wave which is almost entirely in a positive direction. Deep curarization combined with repeated stimulation or with anticholinesterases appear to be the main factors required. It may be dangerous to assume that the observations on isolated ganglia are comparable with those in the intact animal. But they represent striking phenom¬ ena, which remain to be explained on the chemical theory of transmission, and which seem to have no obvious analogue at the endplate. While it is true that repeated stimulation of a motor nerve to a muscle may occasionally produce repetitive firing of synaptic origin when the stimulation is remitted, this is in general an unusual phenomenon. Normally the last stimulus shock is immediately followed by the last muscle action potential. In the ganglion however, repeated stimulation at fairly rapid rates can give rise quite easily to a repetitive discharge which may last for as long as half a minute. Bronk and his colleagues (1) point out that this response may not be of particular biological importance, since the rates of excitation required are probably outside the normal range, but they are still prepared to regard it as a significant characteristic of ganglionic behaviour. Corresponding to this after-discharge is the prolonged facilitation, short of that required for actual ganglionic discharge, which can be observed after sustained excitation of a ganglion, lasting up to five minutes qy more beyond the end of stimulation. Such facilitation occurs also at the neuro muscular sjmapse, but it is a more brief affair. Thus we can say that after repeti¬ tive stimulation of the presynaptic nerve facilitation is greater and more pro¬ longed in the ganglion than in the endplate. Bronk et al. concluded that the facilitation was due to some change produced in the active presynaptic endings. At the neuromuscular junction, it has proved relatively easy to produce de¬ polarization block, and it follows rapidly after the injection of agents such as decamethonium or succinylcholine. Indeed it is not possible to maintain a pro¬ longed stimulant action by such drugs without block ensuing. A dose which is sufficient to initiate a fairly vigorous effector discharge passes on rapidly into block; a smaller dose either produces block more slowly, or its action disappears altogether. At the ganglion on the other hand, it is possible, to produce a vigorous post-ganglionic discharge by means of a continuous infusion of acetylcholine through the stellate ganglion in concentration as high as 100 micrograms per cc., and for these discharges to persist as long as the infusion is maintained (1). Similarly in a cat anaesthetised with chloralose it is quite hard to obtain a relaxa¬ tion of the nictitating membrane preganglionically excited, with a drug such as tetramethylammonium. One could perhaps express the difference by saying that the end-result of the action of a persisting depolarizing drug at the mammalian endplate appears as paralysis complicated by some vestiges of stimulant action; but at the ganglion as persistent excitation behind which some blocking action can be detected. It also appears that the ganglion is less readily influenced by anticholin-