Patterns of Myo-neural Junctions and Cholinesterase Activity in the Muscles of Tadpoles of Xenopus Laevis

1960 ◽  
Vol s3-101 (53) ◽  
pp. 55-67
Author(s):  
P. R. LEWIS ◽  
A.F. W. HUGHES

A simultaneous coupling azo dye technique has been used to reveal the distribution of cholinesterase activity in the musculature of the developing tadpole of Xenopus laevis. The use of inhibitors and a less convenient but more specific histochernical technique confirmed that only true cholinesterase distribution was being demonstrated; and a study of silver-impregnated material proved that this azo dye technique provides a very convenient method of following the development of the patterns of myo-neural junctions in the striated muscles of this tadpole. A wide variety of patterns is seen in the various muscles: in the axial musculature the muscle-fibres become innervated at their ends from myocommatal plexuses and never acquire endings along their length; broad muscular sheets, as in the walls of the branchial and abdominal cavities, are also first innervated terminally from the septa but later acquire secondary innervation is along the lengths of the fibres. These different patterns of innervation are correlated with the functions of the various types of muscle. It is suggested that terminal innervation may be a special adaptation to permit rapid establishment of neurogenic activity, the pattern of endings of the more usual type forming when the need for precisely co-ordinated reflexogenic activity arises. In some muscles, the azo dye technique reveals a profuse multiple innervation of the fibres which are assumed to be of the so-called ‘slow type’ known to exist in some amphibian muscles.

2001 ◽  
Vol 109 (5) ◽  
pp. 410-417 ◽  
Author(s):  
R.T. Jaspers ◽  
H.M. Feenstra ◽  
M.B.E. Lee-de Groot ◽  
P.A. Huijing ◽  
W.J. van der Laarse

1951 ◽  
Vol s3-92 (19) ◽  
pp. 323-332
Author(s):  
M. M. BLUHM ◽  
C. SITARAMAYYA

Myofibrils of rat diaphragm of various ages, in different states of activity, after denervation, and after acetyl choline contracture, were studied by electron microscopy. A comparative study of other rodent diaphragms and of human diaphragm was also made. Myofibrils from diaphragm are similar to those of other striated muscles. The differentiation into A and I bands is due to differences in the substance present round the actomyosin filaments in those regions. The Z disk is extra-sarcomere; it-appears even before any differentiation of the fibril into A and I bands is recognizable. At the age of about 42 days, the myofibrils in rat diaphragm are completely differentiated and conform tothe adult type. The sarcomere length in adult rat diaphragm is between 2 and 3 µ. The adult rat diaphragm contains two types of fibrils which differ, though not sharply, in their extensibility and thickness. The A and I bands react differently to a variety of stimuli. Thus, passive stretching affects the I band almost exclusively, while contraction affects both bands; here, again, the effect depends on the type of contraction; isotonic contraction shortens both A and I, whereas isometric contraction shortens A and lengthens I. In the denervated muscle the A band is shortened. On thewhole, the A band seems to play the major role in contraction. The H disk is intra-sarcomere and appears during contraction, especially when the muscle is stimulated in the stretched state. The M and N lines also are intra-sarcomere. Evidence regarding their nature and appearance is discussed.


Since the end of the 1939-45 war, the task of someone trying to understand muscular contraction has become in some respects easier, and in others more difficult. On the credit side, straightforward explanations are now available—and well established—for the main events in neuromuscular transmission, propagation of the action potential, the inward spread of an activating process, chemical activation of the myofibrils, and the sliding filament process of length change. On the other side new properties, new structures and new substances have turned up which cannot yet be fitted into any comprehensive scheme. Further, we are still totally in the dark about the actual molecular processes involved even in those steps for which clear explanations are available at the electrophysiological or electronmicroscopical level. Yet another complication is the extraordinary variety of muscle types that are being discovered, even among such thoroughly studied groups of animals as amphibians and mammals. I have been repeatedly struck by cases where the investigation of muscle has been held up by a false assumption based on the supposition that different kinds of contractile materials must work in the same way. For example, it has often been argued that smooth muscle and striated muscle are essentially similar, and therefore the striations are of only minor importance; this argument was given, for example, by Bernstein (1901, p. 284). The still more general argument that the nature of the ‘contractility’ of muscle should be looked for in the supposedly simpler processes of protoplasmic movement had been the main theme of a book by Verworn (1892). This attitude was, I am sure, one of the main reasons for the almost complete disregard of the striations by physiologists and biochemists between about 1910 and 1950. Again, the elucidation of the slow motor system of certain striated muscle fibres, present in probably all vertebrates, was delayed for many years by the discovery that in mammals even the slow postural activity of limb and trunk muscles is accompanied by propagated action potentials characteristic of fast motor systems. It was widely assumed on this basis that ‘tonic’ contractions in all vertebrate striated muscles consisted of asynchronous twitches or unfused tetani in scattered motor units, and most physiologists came to disregard the numerous indications—physiological and pharmacological (Langley 1913; Sommerkamp 1928; Wachholder & von Ledebur 1930) as well as histological (see Krüger (1952) for references both to his own work in the thirties and to other work)—of the existence of a second, slow, system in skeletal muscles of the frog. The very slow contractions elicited in the familiar gastrocnemius muscle of the frog by stimulating small-diameter motor-nerve fibres (Tasaki & Kano 1942; Tasaki & Mizutani 1944; Tasaki & Tsukagoshi 1944) came as a complete surprise to most physiologists, and received little attention until the matter was taken up by Kufiler and his colleagues (e.g. Kuffler & Vaughan Williams 1953). The astonishing range of structural diversity that becomes apparent when one looks at the arthropods as well as the vertebrates has recently been emphasized by Hoyle (1967).


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