Transmission at the mammalian neuromuscular junction
Date
1956
Authors
Liley, Albert William
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Abstract
For more than a century vertebrate nerve-muscle preparations have been extensively investigated. This is not surprising for such preparations are readily accessible and may survive, isolated, in simple solutions for many hours. Furthermore the mechanical response of muscles to direct and indirect stimulation provided some index of activity long before electrical recording techniques were evolved. The concept of the neuromuscular junction as a physiological entity dates from the researches of Claude Bernard on in 1850-57. The work of Langley (1950, 1907) indicated the pharmacological specificity of the muscle junctional region. Following the demonstration of the release and action of acetylcholine at the neuromuscular junction (Dale, Feldberg & Vogt, 1936; Brown, Dale & Feldberg, 1936) and the electrical recording of the end-plate potential (Gopfert & Schaefer, 1936; Ecoles & O'Conner, 1939; Feng, 1940) knowledge of neuromuscular transmission has advanced rapidly and numerous reviews have been published (Feng, 1941; Ecoles, Katz & Kuffler, 1941; Whitteridge, 1948; Acheson, 1948; Harvey, 1948; Kuffler, 1948; Toman & Goodman, 1948; Koelle & Gilman, 1949; Paton, 1949; Hunt & Kuffler, 1950; Rosenblueth, 1950; Tiegs, 1953). In the present decade progress has followed the application of two elegant and powerful techniques to the problems of junctional transmission. First, the intracellular microcapillary method of electrical recordings has allowed precise investigation of the behaviour of single muscle fibres and junctions. Secondly, electron-microscopy has displayed important detail in both the pre- and post-synaptic components of the junction. The information yielded by these new techniques has been reviewed by Fatt (1954) and Castillo & Katz (1956b). Of particular interest was the observation by Fatt & Katz (1950) that the amphibian and reptilian myoneural junctions were the site of spontaneous subthreshold activity. This activity consisted of intermittent small potentials which resembled the e.p.p. except for their briefer timecourse. Hence these small potentials were designated "miniature e.p.p.s" or "miniature potentials". Fatt & Katz (1950, 1952, see also 1953) produced evidence that the miniature potentials were generated by multimolecular packets or quanta of acetylcholine which were released spontaneously from the motor nerve terminals. The significance of this phenomenon was established by Castillo & Katz (1954b) when they demonstrated that, in the frog, the e.p.p. was produced by the synchronous discharge of a large number of these quanta of acetylcholine. The extensive investigations of Castillo and Katz (1954a-d, 1955a,b, 1956a) have added further detail of the release and effect of the quanta of transmitter at the amphibian myoneural junction. These researches have shown that transmission is graded at the quantal and not the molecular level. <…>
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Keywords
neural transmission, myoneural junction
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Type
Thesis (PhD)