Changes in the structure of the myelinated nerve fibre with chemicals

Transcription

1 Changes in the structure of the myelinated nerve fibre with chemicals II. Structural changes of the nerve fibre owing to ph changes of the medium By Hidehiko Takahashi, Juro Maruhashi, Morio Ihnuma, Kimitoshi Ishida and Moritomi Kubo In this paper, our main concern is the changes in the structure of the myelinated nerve fibre caused with changes in ph of the surrounding media. Materials and Methods The preparation of materials and the method of the microscopic observation may be referred to the preceeding paper (1). In order to change the ph of Ringer solution, a suitable quantity of N/10 NaOH or HCl was added. The ph of the Ringer solution as the control was 6.8. Results Under the action of the media whose value of ph was more than 8.0, changes in the microscopic structure of the myelin sheath occurred. At first, the change in the incisions of Schmidt-Lantermann came in sight and then the whole part of the myelin sheath appeared as if it had been deprived of its configuration. At the same time, the myelin became oily and at last the flowing of myelin started. Plate 1 shows the changes in the incisions of Schmidt-Lantermann under a ph of 1. Department of Physiology, Kumamoto University, Kumamoto. 2. Department of Physiology, Tokyo Medical College, Tokyo. 3. Department of Anatomy, Tokyo Woman's Medical College, Tokyo. 4. Department of Anatomy, School of Medicine, Keio-Gijuku University, Tokyo.

2 236 H. Takahashi, J. Maruhashi, M. Ihnuma, K. Ishida and M. Kubo The incisions opened widely and were gradually increased in their depth, invading the axon. Figs. 23a---g. in plate 4, show the staining with surplus quantia of 0.5 % osmic acid solution of above mentioned preparation. The staining was applied, after the changes in the structure became remarkable. The photographs were recorded, changing foci by 2 fh. From the finding in these photographs, it is evident that the myelin deeply invaded the axon beneath the incisions near the Ranvier's node. Plate 3 shows the flowing of myelin under a ph of In this case, the swelling of the myelin sheath started accompanying the changes in incisions. In 1-2 minutes, the flowing of myelin took place. The myelin flow was observed most easily at the Ranvier's node. The myelin sheath which was interrupted at the Ranvier's node continued and fused with each other, Myelin went across the Ranvier's node. Sometimes, a few vacuoles were observed in myelin and these vacuoles flowed across the Ranvier's node considerably rapidly. But the emulsifying of myelin was not observed in all the experiments. After the flowing continued for a while, myelin discontinued again at the Ranvier's node and was separated from each other. Then, the flowing myelin gradually accumulated near the Ranvier's node. When the pressure of accumulated myelin got over its surface tension, the myelin on both sides of the Ranvier's node fused with each other and the flowing started again. These phenomena were repeated and all the myelin at the neighbourhood of the node flowed away. Then the nerve fibre appeared as if the configuration had been lost completely. The flowing myelin remained a little in the region near the cut end and in the incisions near the Ranvier's node. It should be noticed that oily myelin flowed out by no means from the nerve fibre except from the cut end. Photographs in plate 2 record the changes in the structure along the longitudinal axis of the fibre under a ph of The preparation was stained with 0.5% solution of osmic acid after alkali had given rise to changes. The changes in the structure of incisures were most remarkable near the Ranvier's node and not so severe at the middle of the internodal segment. Sometimes, the effect of alkali was so severe that the fibre was cut into pieces. In such case, the experiment was given up. In fact, plate 2 shows the figure of the cutting of the fibre. An example of the observation in the acid medium is shown in of plate. Under acidity, the opening and increase in the depth

3 Changes in the structure of the myelinated nerve fibre with chemeicals II. 237 were also observed in incisures. A characteristic change was the stiffening of the axon. Discussion According to previous reports, the incisure of Schmidt-Lantermann changes its appearance, after repetitive stimulation (2). The authors also observed structural changes in the incisure with various chemicals. So, the change in the structure of the incisure is not speicific to the action of alkali or acid. Under the effect of alkali or acid, the incisure was pulled to enlarge its width owing to the swelling of the myelin sheath. But, with this cause only, the increase in its depth can not be explained. It has been known that the Ranvier's node which was devoid of the myelin sheath has suffered most easily from chemicals (3). Consequently, it is tenable to assume that incisures which lack myelin, are also at first affected by chemicals and the most remarkable changes in the structure take place there. This assumption agrees with the fact that the incisures nearest the node suffered most prominent. The invasion of myelin into the axon occurred beneath incisures and did not take place in any other regions. On the other hand, oily myelin did not flow out from the nerve fibre. This finding enables us to think that myelin is put in between the concentric two cylindrical membranes which are able to resist alkali or acid. Of these membranes, the external membrane packed the whole fibre, including the nodes. This membrane is perhaps the neurilemma. The internal membrane continued across the nodes, and was supposed to be the plasma membrane. This membrane was interrupted at the incisures or the axon beneath the incisure became soft easily, permitting the subsidence of the plasma membrane with myelin. This question is left undetermined. From our observation, the following facts have become evident the neurilemma continues at the incisures and the nodes, packing the whole fibre. The membrane does not adhere closely to the axon at the node, but a space may exist between them, at least following the the administration of alkali. When the myelin sheath was injured, myelin flowed out into the medium and dispersed in the medium as small droplets. On the contrary, when alkali made myelin to flow, myelin was not emulsified, but only oily. This change was similar to the change of fat into oil

4 238 H. Takahashi, J. Maruhashi, M. Ihnuma, K. lshida and M. Kubo with heating. Acid caused the stiffening of the axon. This structural change enables us to suppose that acid can cause increase of the electric resistance of the axon. In the normal state there is electric leakage from the myelin sheath (3). About the relation between this leakage and Schmidt- Lantermann's Incisure, there has been no article issued. Our microscopic observations and Funasak a's (4) electric measurements showed that some relation may exist between the electric leakage and the dimensions of incisures. Summary 1. In the alkaline medium, the structure of the nerve fibre began to change at first in Schmidt-Lantermann's incisures and at last structural changes spread to all the parts of the myelin sheath. 2. Alkali gave rise to change of incisures easily and enlarged its widening, accompanied with the increase in its depth. 3. The structural change was the most prominent in the incisures near the node and not so remarkable in the incisures at the middle of the internodal segment. 4. The change of the myelin sheath caused with alkali consisted of the swelling and the liquefication of myelin. In strong alkali, solid myelin became oily and started to flow. 5. The oily myelin flowed across the node, but did not flow out from the fibre, including incisures. From the cut end, myelin flowed away and dispersed in the medium. 6. The most plausible interpretation of the phenomenon may be an assumption of the existence of a sheath which packs the whole fibre, including the incisures and the nodes. It has been known that the nerve fibre has only two sheaths. And neurilemma can act as such a sheath. The observation of myelin flow across the node enabled us to assume that neurilemma does not adhere closely to the axon at the node. 7. Acid caused similar changes in the structure of incisure. A characteristic change induced with acid was the stiffening of the axon. 8. The relation between the electric leakage from the normal myelin sheath and Schmidt-Lantermann's incisure was assumed from our microscopic observations and electrical measurements. This investigation was carried out in the laboratory of the Depart-.

5 Changes in the structure of the myelinated nerve fibre with chemicals 239 ment of Anatomy of Keio-Gijuku University by courtesy of Prof. T. Taniguchi. The authors acknowledge his kindness deeply. Literatures 1. M a ru h a s hi, J. et al. Changes in the strucure of the myelinated nerve fibre with chemicals. I. Method and structural changes in the nerve fibre owing to the hypertonic medium. Fol. anat. jap., 29: B a u-i( in-ts i ng, Die Funktion und Bedeutung der Schmidt-Lantermannschen Einkerbungen. Mitt. d. Med. Fak. d. Staatl. Univ. Peking, 1/2 :1, T a s a k i, I. Nervous transmission, C. C. Thomas, F unas a ka, Y. The effect of various chemicals on the myelin sheath. J. Physiol. Soc. Jap. 16: 697, 1954 Explanation of Plates Fig. 1, 2. Toad's normal myelinated nerve fibre in Ringer (control). 1 The part near the Ranvier's node (a). 2 The part of the internodal segment (b). R. T. 16 C. Figs. 3, 4. Same fibre, 3 min. after the application of the Ringer of ph The part (a). 4 The part (b). Figs. 5, 6. Same fibre, 6 min. after the application. 5 The part (a). 6 The part (b). Figs. 7, 8. Same fibre, 14 min. after the application. 7 The part (a). 8 The part (b). Figs. 9, 10. Same fibre, 20 min. after the application. 9 The part (a). 10 The part (b). Fig. 11. The same fibre as that shown in the plate I. The staining with 0.5% osmic acid was done 30 min. after the application of the Ringer solution of ph The whole length of the single nerve fibre was photographed in order to compare change in incisures near the Ranvier's node with the change in those of the internodal segment. Fig. 12. Toad's normal myelinated nerve fibre in Ringer (control). R.T. 16 C. Fig. 13. Same fibre, 2 min. after the application of the Ringer of ph Fig Same fibre, respectively 4, 5, 6, 7, 10, 19, 27, 34 min. after the application. Fig. 22. Same fibre, the part near the cut end. 44 min. after the application. Figs. 23 a-g. The same fibre as that in plate I. The staining With 0.5% osmic acid, was done 30 min. after the application of the Ringer of ph These photographs were taken at successive levels, each 2 IA. Fig. 24. Another toad's myelinated nerve fibre in Ringer (control) R. T. 18 C. Fig. 25. Same fibre, 10 min. after the application of the Ringer of ph Fig. 26. Same fibre, 18 min. after the application.

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9 Plate IV H. Takahashi et al.