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The Autonomic Nervous System of Selachians. by John Z

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The Autonomic Nervous System of Selachians. by John Z The Autonomic Nervous System of Selachians. By John Z. Young, B.A. With 28 Text-figures. CONTENTS. I. INTRODUCTION ......... 571 II. MATERIAL AND METHODS 572 III. ANATOMY AND HISTOLOGY OF THE SYMPATHETIC SYSTEM . 575 1. Nature of the Rami Communicantes .... 575 2. Anterior Eami Communicantes and Sympathetic Ganglia 581 3. Anatomy of the Sympathetic System in the Trunk . 581 4. Sympathetic System and Suprarenals in the Kidney Kegion 586 5. Sympathetic System in the Tail ..... 589 6. Autonomic Fibres in Spinal Dorsal Roots . 593 7. Cytology of the Sympathetic Ganglia .... 593 8. Relation of the Sympathetic Cells to the Suprarenal Tissue 598 9. Post-Branchial Plexus 600 IV. INNERVATION OF THE VISCERA 603 1. Nerves of the Alimentary Canal ..... 603 2. Innervation of the Urinogenital System . 609 3. Cardiac Nerves 610 V. CRANIAL AUTONOMIC SYSTEM 610 1. Autonomic Fibres in Branchial Nerves . 610 2. Profundus and Ciliary Nerves ..... 614 VI. PHYLOGENETIC HISTORY OF THE AUTONOMIC NERVOUS SYSTEM 617 VII. SUMMARY. 621 VIII. BIBLIOGRAPHY 623 I. INTRODUCTION. THE only complete account of the sympathetic nervous system of Selachians is that of Chevrel published in 1887. Since that date several papers have appeared dealing with special points of structure or function, such as those of Bottazzi (1902), Muller and Liljestrand (1918), and Lutz (1981), on the innerva- tion of the viscera; of Diamare (1901) on the histology; and of NO. 300 o o 572 JOHN Z. YOUNG Hoffmann (1900), Miiller (1920), and others, on the development. No attempt has yet been made to investigate the autonomic nervous system of these fish from the general standpoint intro- duced by Langley (1921) and Gaskell (1915); this the present study attempts to do. Its aim has therefore been to give an accurate account of the anatomy and histology of the system with special reference to the functions of the neurones, in order to discover whether the system conforms to the same general plan as that of mammals and whether any conclusions can be drawn either as to its phylogenetic history, or, in general, as to its nature and function. A similar study has recently been made on a Teleostean fish (Young, 1931), and the problems involved are there discussed. II. MATERIAL AND METHODS. The following is a list of the Selachians used in the in- vestigation: Order Selachii. Group 1. Notidani. Heptanchus cinereus. Group 2. Sub-order 1. Scyllioidei. Scyllium canicula. Scyllium catulus. Mustelus laevis. Mustelus vulgaris. Careharias glaucus. Sub-order 2. Squaliformes. Squalus acanthias. Sub-order 3. Eajiformes. Torpedo ocellata. Torpedo marmorata. Trygon violaceus. The great majority of the observations were made on S c y 1 - AUTONOMIC SYSTEM OF SELACHIANS 573 Hum (= Scylliorhinus) canicula, the other species being used only for comparison as regards the more important points. Most of the work was done at Naples during three visits in 1928, 1930, and 1931, when use was made of the Oxford and British Association Tables, for both of which I am very grateful, as also for the many facilities and constant assistance given to me by Professor Dohrn and all of the staff of the Station. Some material was collected at Plymouth during a short but fruitful stay at the Marine Laboratory in 1931, for which I wish to thank Dr. Allen. Much of the histological work was done in the Department of Zoology and Comparative Anatomy at Oxford, and I have to thank Professor Goodrich for much stimulating advice. For many purposes it was desirable to anaesthetize the dog- fish, and the best method was found to be immersion in a liquid made by diluting a 10 per cent, solution of chloretone in 95 per cent, alcohol with 99 parts of sea-water. In this they became motionless in 1-3 minutes and remained anaesthetized until revived by a stream of water passed over the gills. 2 per cent, solutions of urethane and subcutaneous injections of a 20 per cent, solution of the same were found to be effective, but less satisfactory than chloretone. Ether anaesthesia was found to be unsatisfactory. For study of the macroscopic anatomy of the sympathetic nervous system, use was made of the osmium tetroxide method, the advantages and limitations of which have already been discussed (Young, 1931). For closer study of the nerves the methods of Cajal and Bielschowsky were used with success. The most satisfactory preparations were obtained by injection of the fixative after light anaesthesia, a cannula being inserted into the ventral aorta just in front of the heart. The rest of the technique was then as follows: (1) Pieces excised and left for 24 hours in the fixative: Chloral hydrate 5 gm. Isotonic Selachian solution1 100 c.c. 1 For the methods of preparing isotonic solutions for use with Selachians see Young, 1932. 0 0 2 574 JOHN Z. YOUNG (2) Wash for 24 hours in changes of distilled water. (3) Pass slowly up the alcohol series to 95 per cent., in which leave for 24 hours. (4) Down the alcohol series to water and thence to 1-5- 2-5 per cent, silver nitrate at 87° C. for 4 to 6 days. (5) Short wash in distilled water (1-5 minutes according to the size of the pieces). (6) Eeduction in hydroquinone or pyrogallic acid 1 gm. neutral formol 10 c.c. distilled water 90 c.c. The hydroquinone reduces more violently and gives the more clear-cut pictures, but the lighter stains obtained with pyro- gallol often show more detail. (7) Dehydrate rapidly, embed in paraffin wax and cut sections 15-30fi thick; or alternatively, since the gan- glia are very thin, whole mounts could be made in Apathy's syrup or Canada balsam, and these were found to be very useful. This method was varied in several ways, the following being the most successful methods: (1) Fix in 95 per cent, alcohol plus 1 drop of NH3 per 10 c.c. (2) Wash in distilled water and transfer to pyridine for 24 hours. (3) Wash in changes of distilled water until no smell of pyridine remains. (4) Proceed as above. Or another method: (1) Fix for 24 hours in chloral hydrate 2-5 gm. 95 per cent, alcohol 40 c.c. distilled water 40 c.c. pyridine 20 c.c. (2) Proceed as in the first technique. A number of preparations were made with the methylene blue technique, after injection of the stain, but the best prepara- tions obtained in this way did not equal those obtained by Cajal's method. Gold chloride (Lowit's method) was found to AUTONOMIC SYSTEM OF SELACHIANS 575 be useful for study of the shape of the cells, but did not stain the finer fibres. For study of the suprarenal and interrenal systems pieces were fixed in Flemming's fluid and various formol-bichromate mixtures, of which Wiesel's fluid was found to be the most satisfactory. The best results were obtained when the solutions were made up with isotonic solution. III. ANATOMY AND HISTOLOGY OF THE SYMPATHETIC SYSTEM. 1. Nature of the Eami Communicantes. The sympathetic system of Selachians differs in its funda- mental plan from that of all other vertebrates. In each segment in which it occurs there are one or more ganglia connected with the corresponding spinal nerve by a ramus communicans which consists of medullated pre-ganglionic fibres only, there are no recurrent grey rami communicantes. This condition has been revealed by study of whole mounts of rami communicantes stained with osmium tetroxide. After this treatment it can be seen that the fibres in the rami are all medullated and that at the point of junction with the spinal nerve they always turn inwards and can be followed for a considerable distance towards the central nervous system (Text-figs. 1 and 2). There are no medullated or non-medullated fibres turning outwards or run- ning peripherally to be distributed with the spinal, nerves, although such fibres if they were present would certainly be revealed by this method as they are in mammals (Miiller, 1924, fig. 11) and in Teleosts (Young, 1931, fig. 3). Besides the fine medullated pre-ganglionic fibres the rami communicantes also contain sensory fibres which are very large and can be traced individually to the sense organs concerned (see p. 602). The fact that all the motor-fibres in the rami communicantes are pre-ganglionic can be confirmed by means of preparations stained with Cajal's method, in which it can be seen that all the fibres run out to the sympathetic and none backwards from the sympathetic to the spinal nerve (Text-fig. 3). Kami communicantes from all levels have been examined in JOHN Z. YOUNG TEXT-FIG. 1. S c y 11 i u m c a n i c u 1 a. Origin of ramus communicans from spinal nerve. OsO4, whole mount. W. Watson 2/3 in., camera lucida. EXPLANATION OF LETTERING. a., amphicyte; a.m.a., anterior mesenteric artery; art., artery; ax., axillary body; b.a., brachial artery; br., branch of non-medul- lated fibres; c.a., coeliac artery; c.v., cardinal vein; cil.a., anterior ciliary nerve; cil.p., posterior ciliary nerve; or., chrome-staining tissue; d., dendrite; d.a., dorsal aorta; e.p.a., efferent pseudo- branchial artery; /., nerve-fibres to chromophil cells; g., gastric ganglion; g.dl., ciliar)' ganglion; gl., dendritic glomerulus; h., heart; in.,intestine; int.,interrenal tissue; k., kidney; I.e., longi- tudinal connective; n., nucleus of nerve-cell; n.art., nerve to artery; n.c, nerve-cell; n.v., nerve to viscera; not., notochord; o. V+ VII., rr. ophthalmici V+VII; oes., oesophagus; p., pre-gan- glionio fibre; p.b.c, cell of post-branchial plexus; p-b.g., post- branchial ganglion; p.b.p., post-branchial plexus; ph., pharynx; pr., r.
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