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L Ocalization of the Neurons of Origin of Efferent Fibers in The Okajimaslia Anat. Jpn., 61(4): 287-310. October 1984 L ocalization of the Neurons of Origin of Efferent Fibers in the Glossopharyngeal, Vagus and Accessory Nerves in the Rat by Means of Retrograde Degeneration and Horseradish Peroxidase Methods By Yong Li LU and Hisashi SAKAI Department of Anatomy, School of Medicine, Nagoya University, Nagoya 466, Japan -Received for Publication, July 4,1984- Key Words: Dorsal motor nucleus of vagus, Ambiguus nucleus, Localization, Retrograde degeneration, HRP. Summary: In order to pursue further the possible localization of the functional centres which belong to the group of the glossopharyngeal, vagus and accessory nerves, the motoneurons of these nerves and their major branches in the rat were examined by the retrograde degeneration method and the horseradish peroxidase (HRP) method. The results obtained are based on the examination of 62 rats which were divided into five groups. The results obtained are as follows: (A) The vagus nerve arises from 80-90% of neurons of the dorsal motor nucleus of the vagus (DMV), the total neurons of the ambiguus nucleus (AM) except for a few cells occupying the ventral part of its rostral region, the neurons of the reticular formation between the DMV and the AM, and the neurons of the lateral reticular formation ventrolateral to the AM. (B) The motoneurons of the superior laryngeal nerve innervating the laryngeal muscles comprise 20% of the total cells in the DMV and 50% of the neurons in the rostral one-third of the AM, but the motoneurons of the recurrent nerve are present only in the caudal two-thirds of the AM. (C) Fifty to 60% of the neurons of the DMV supply the abdominal organs. The cell mass forms a series of columns, which is located in the lateral part of the rostral region, the central and medial parts of the middle region and the medial part of the caudal region of the DMV. (D) The glossopharyngeal nerve does not arise from the DMV but from the neurons which are located at a more rostral level than the DMV and from the most rostral and the ventro-rostral parts of the AM. (E) The results also indicate that the vagus nerve consists of elements not only from the vagus nerve but also from the internal branch of the accessory nerve. The neurons of the internal branch of the accessory nerve are scattered in the caudal region of the DMV and the AM. The external branch of the accessory nerve does not arise from the DMV and the AM, but from neurons located in the lateral area of the anterior horns extending from the first to the fourth cervical segments of the spinal cord. These findings were consistently ipsilateral to the side operated on. It is well known that the efferent fibers (AM), which contain many neurons involv- in the vagus nerve originate from two ing respiratory, cardiovascular, and gastro- distinct nuclei, the dorsal motor nucleus of intestinal functions (Whitteridge 1948. Getz vagus (DMV) and the ambiguus nucleus and Sirnes 1949, Paintal 1953, Mohiuddin *Present address: Department of Anatomy , China Medical College, Shenyong, China 287 288 Yong Li LU and H. Sakai 1953, Mitchell and Warwick 1955, Calaresu the previous studies. In order to pursue the and Cottle 1965, Sugimoto et al. 1979, possible topographical location of the Kalia and Mesulam 1980a, 1980b). Further- functional centres which belong to the more, determination of a possible specific group of the glossopharyngeal, vagus and topographical arrangement within these accessory nerves, the motoneurons of nuclei has been attempted. Earlier, Molhant efferent fibers in these nerves and their (1910) and Getz and Sirnes (1949) provided major branches in the rat have been ex- anatomical reports with regard to the DMV amined by means of the methods of the in rabbits and described the definite topo- retrograde degeneration and the retrograde graphical localization in relation to various transport of HRP. visceral organs in this nucleus by the retro- In the present study, in order to deter- grade degeneration method. Since then, mine the presence or absence of localiza- many other studies in several animal species, tion of the motoneuron in the DMV and cat (Mohiuddin 1953, Smolen and Truex the AM, the vagus trunk and its branches 1978), monkey (Mitchell and Warwick innervating the larynx via the superior 1955), sheep (Bell and Lawn 1955, Welento laryngeal and the recurrent nerves and and Flieger 1974), buffalo (Rao and Sahu branches innervating the abdominal organs 1974), and fowl (Watanabe 1968), have via the anterior and posterior abdominal indicated the definite topographical localiza- trunks of the vagus were cut and examined. tion within this nucleus by the same meth- In addition, in order to determine whether od. In addition to these studies similar the DMV anastomoses with other nerves, attempts have been made at topographical the glossopharyngeal nerve and the internal location in the AM of the rabbit (Lawn and external branches of the accessory 1966a, 1966b). nerve were also cut and examined. Recently, the retrograde transport of horseradish peroxidase (HRP) has been Materials and Methods used to identify more exactly the cells of origin of efferent fibers supplying the A total of 60 male and female Wistar visceral organs (Todo et al. 1977, Yama- rats weighing 200-500 g were used in the moto et al. 1977, Satomi et al. 1978, Nosaka present experiment. The animals were et al. 1979, Kalia and Mesulam 1980a, anesthetized with 5% sodium pentobarbital 1980b, Wild 1981, Contreras et al. 1980, (i.p. 50 mg/kg). All animals were divided Nomura and Mizuno 1981, 1982). into five experimental groups and operated However, since certain differences are on. The materials were prepared by the recognizable among the species, the loca- methods of retrograde degeneration and tions of the motoneurons in the species retrograde transport of HRP. The numbers do not seem to be fully described as yet. of animals used, plane transected and Few studies have been carried out on the procedures employed for each group are DMV and the AM of the rat. In addition, illustrated in Figs. 1A, I B and Table 1. there are some questions: do the efferent a) Retrograde degeneration method fibers of the vagus nerve originate from The animals under anesthesia were nuclei other than these two, and do these operation on and the nerves were transected two nuclei give the fibers to nerves other at five sites in the cranial and cervical than the vagus nerve? With regard to these regions and the region of the glandular questions, there are discrepancies among stomach (Figs. 1A and 1B). Under an Neurons of Origin in Rat Gloopharyngeal. Vagu and AcceN%or Nerves 289 Fig. 1. Diagrams showing the five levels (1 to 5) of transected sites in the glossopharyngeal, vagus and accessory nerves. A, in the cranial and cervical regions. B, in the glandular stomach region. Table 1. Schematic presentation of the sites of neurectomy 290 Yong Li LU and H. Sakai operation microscope, the nerves were hours postoperatively, and then deeply re- exposed and dissected free from the sur- anesthetized and perfused through the left rounding tissue. A small piece of the nerve, ventricle with 300-500 ml of 0.9% saline about 0.3-1.0 cm in length, was excised solution at room temperature. This was to avoid contact of the terminals. After followed by 500 ml of 1.0% paraformal- the operation, the animals were allowed dehyde and 1.25% glutaraldehyde in 0.1 M to survive for 8-14 days. After anesthetiza- phosphate buffer (pH 7.2-7.4) and then tion by the same method the animals were by 500 ml of 10% sucrose in the same perfused through the left ventricle with buffer. The brain with the cervical segment 10% formalin, then the brains with the of the spinal cord was removed and stored cervical segments of the spinal cord were in 10% sucrose in phosphate buffer, pH removed and postfixed in 10% formalin 7.2-7.4, for 2-24 hours at 4°C, and then for three to four weeks. Then the brains cut transversely into serial 50 pm thick were washed, dehydrated and embedded sections on the freezing microtome. The in paraffin. Serial 10 pm thick sections sections were treated by the tetramethyl- were made transversely in all materials. benzidine (TMB) method of Mesulam The first of every four sections was stained (1981) for the histochemical demonstration with cresyl violet and examined. The judge- of HRP, then mounted on gelatinized ment as a degenerative cell was based on slides and counterstained with 1% neutral three standards: (1) neuronal swelling of red solution. They were examined micro- the cell body, (2) eccentricity of the nuclei, scopically under bright-field and dark- (3) fragmentation of the Nissl substance. field illumination. The counting of degenerative neurons The present results are almost all based was based on those counted in the first on observations obtained by the two meth- of every four sections. Then multiplying ods at the same sites except for the internal by four gave the total number of degen- branch of the accessory nerve which was erative neurons. The proportion of degen- treated only by the retrograde degenera- erative neurons in normal cells was deter- tion method because this branch is too mined as previously described and found to short for HRP bathing. be about 5,000 cells in each DMV in the rat (Li' and Sakai 1984). Results b) HRP method As in the method described above, the Group 1. The motoneurons of the vagus nerves were transected and dissected free nerve from the surrounding tissues which were In the first group of 12 rats, the right or covered with a piece of parafilm in order left cervical vagus trunk was transected at to avoid any undetected uptake of HRP.
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