The pharmacology of the toxiferines / by W.D.M. Paton and W.L.M. Perry.

  • William Paton
Date:
[1951?]
Catalogue details

Licence: In copyright

Credit: The pharmacology of the toxiferines / by W.D.M. Paton and W.L.M. Perry. Source: Wellcome Collection.

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    muscle, by observing that the response to direct stimulation of a cat’s tibialis, fully paralysed to stimulation through its nerve, was completely unaffected. The usual way to demonstrate that a paralysis is not due to interference with conduction in the motor nerve is to record normal action potentials from the trunk of the nerve. The recording of an endplate potential, however, from a muscle paralysed with toxiferine, serves the same purpose. When the nerve impulse is blocked there is naturally no endplate potential; if, on the other hand, the nerve impulse is not blocked, a normal propagated response of the muscle fibre is elicited and the end¬ plate potential is obscured by a spike potential. In neither case, therefore, can pure endplate potentials be recorded. Their occurrence, therefore, on nerve stimulation during motor paralysis is proof of block at the myoneural synapse. During paralysis after toxiferine I such pure endplate potentials can in fact be recorded, and Fig. 1 shows two endplate potentials recorded from the endplate region of a cat’s gracilis after a dose of 200 yg. toxiferine I intravenously ; the upper record is with complete paralysis, and the lower record was taken during partial recovery and shows the beginning of propagated spikes. i--—- i 10 msec. Fig. 1.—Cat, chloralose, gracilis. Records of endplate potentials. Electrodes on musculotendinous junction and endplate region. Intravenous injections, (a) After toxiferine I, 200 fig.; (b) later, during recovery from same dose of toxiferine f. a bed Fig. 2.—Cat, chloralose. Record of contractions of tibialis excited by supramaxirpal shocks to the sciatic nerve every 10 seconds. Intra¬ venous injections. At (a) toxiferine VT, 20 fig./kg.; at (b) tetanus, 25 shocks per sec. for 10 sec.; at ( ) atropine sulphate, 0.3 mg./kg.; and at (d) prostigmine methyl- sulphate, 0.3 mg./kg. Characteristics of neuromuscular block by toxiferines.—Several characteristic features of toxiferine-induced block of the cat’s tibialis to nerve stimulation are shown in Fig. 2 ; 20 /xg./kg. of toxiferine VI causes, after a latency of about one minute, a smooth and rapid onset of block. There is no preceding potentiation of the tension of the single twitch, nor any sign of muscular fasciculations ; both these phenomena are typical of block by decamethonium and are absent with d-tubo- curarine. Atropine causes a slight intensification of the effect of toxiferine VI. Prostigmine, given after the atropine, reverses the block very rapidly and even
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