Indmedica Home | About Indmedica | Medical Jobs | Advertise On Indmedica
Search Indmedica Web
Indmedica - India's premier medical portal

Journal of the Anatomical Society of India

Nuclear origin of the efferent fibres of the hypoglossal nerve in the monkey (Macaca radiata)

Author(s): Saraswathi, P.

Vol. 52, No. 1 (2003-01 - 2003-12)

Department of Anatomy, Stanley Medical College, Chennai INDIA

Abstract. The efferent functional component and nuclear origin of the constituent fibres of the hypoglossal nerve is not clear. Thepresent study used horseradish peroxidase (HRP) retrograde tracing technique in hypoglossal nerve in the monkey (Macaca radiata) tofind the nuclear origin of the constituent motor fibres of the hypoglossal nerve. HRP delivery in the right hypoglossal nerve has shown thatthe constituent somatomotor fibres of the hypoglossal nerve originate bilaterally from the hypoglossal nucleus and bilaterally fromperihypoglossal nuclei and that the visceromotor fibres from the ipsilateral dorsal motor nucleus of the vagus. This is demonstrated andreported in the monkey (Macaca radiata) for the first time.

Key words: Dorsal motor nucleus of vagus; efferent; horseradish peroxidase; Hypoglossal nerve; hypoglossal nucleus; monkey;

perihypoglossal nuclei.


The hypoglossal nerve is motor to most of the muscles of the tongue. Hypoglossal nucleus corresponds with hypoglossal triangle in the medullary part of the floor of the fourth ventricle and extends into the closed part of the medulla oblongata, where it is anterior and paramedian to the central grey matter (Williams et al, 1995).

The hypoglossal nerve communicates with the sympathetic trunk, vagus, pharyngeal plexus, first and second cervical nerves, and lingual nerve (Williams et al,1995; Chhatri and Berk, 1997) A large communicating ramus is found between the hypoglossal nerve and inferior ganglion of vagus in human fetuses (Wozniak and Young, 1968) but not in rabbits (Boyd, 1941).

The efferent functional components and nuclear origins of the constituent fibres of the hypoglossal nerve are not clear. In the preliminary work of the author in the monkey, nerve fibres from the medial part of the hypoglossal nucleus crossed over to the opposite side and the hypoglossal nerve was formed by the union of two limbs, the medial limb from the opposite side and the lateral limb from the same side (not shown). Resection of the hypoglossal nerve in the monkey was followed by chromatolysis of neurons in the hypoglossal and perihypoglossal nuclei bilaterally, and in the dorsal motor nucleus of vagus ipsilaterally (not shown). Therefore, to establish these observations, the present study was made, using horseradish peroxidase (HRP) retrograde tracing technique, to find the nuclear origin of the constituent motor fibres of the hypoglossal nerve.

Material and Methods:

Six adult bonnet monkeys (Macaca radiata) were used for HRP retrograde tracing experiments on hypoglossal nerve. HRP, obtained from Sisco Research Laborataries, Bombay, was used. Following thiopentane sodium anaesthesia (30 mg/kg I/V), resection (axotomy) of the right hypoglossal nerve was performed, opposite the descendens hypoglossi, in the side of the neck. One tenth of a millilitre of 30% solution of HRP was injected, using a tuberculin syringe fitted with a No. 25 needle. The needle was introduced inside the epineurium of the proximal cut end of the hypoglossal nerve for about 0.5cm parallel to the nerve and HRP was slowly injected under minimum pressure. The injection lasted 15minutes. To ensure influx of HRP into the axons, the cut end of the nerve was dipped into a solution of HRP.

Twenty four to forty eight hours after resection, under thiopentane sodium anaesthesia, the animals were perfused with normal saline, followed by 10% formol saline fixative. The perfusion apparatus needle was introduced through the left ventricle of the heart and the right atrium was opened for bleeding (Rosene and Mesulam, 1978).

The skull was opened. The medulla oblongata was removed and immersed in 10% formol saline for 3 to 3½ hours. The fixation was terminated by immersing the medulla in a sucrose buffer solution consisting of 10% sucrose in 0.1M phosphate buffer at pH 7.4 and kept at 4°C. The medulla was stored in this solution till it sank.

Twenty-micron thick transverse sections were cut using a freezing microtome. The sections were collected in sieve plates having 0.1M phosphate buffer, mounted on glass slides and viewed under microscope.

Ther nerve cells were counted in an area of 48400 square microns, using a Reichert Wien eyepiece and the number per 100 square microns (percentage) was calculated.


Reaction products were found in the nuclei within 36 to 48 hours after intra-axonal injection of the HRP into the proximal cut end of the hypoglossal nerve. The blue reaction product was in the cytoplasm and in the proximal dendrites of the nerve cells. The nucleus and nucleolus were not stained by the reaction product. Processes were observed, giving the neurons the typical appearance of a multipolar neuron.

Hypoglossal nucleus:

Most of the neurons in the hypoglossal nucleus on the right side (side of resection) and a few neurons in those on the opposite side were labelled with HRP (Fig.1.). THe reaction products were seen in the cells along the course of the hypoglossal nerve. HRP-positve neurons (Fig.2) were seen bilaterally in closed and open medulla. In the closed medulla, the neurons were labelled equally on the right and left sides. In the open medulla, more labelled neurons were present on the right side than on the left and were close to the midline. On the right, 4.66 + 0.35 percent of labelled cells and on the left, 2.66 + 0.22 percent of lebelled cells were present.

Perihypoglossal nuclei.

Labelled neurons were present in the perihypoglossal nuclei (Fig.3) of both right and left sides. They were small-sized cells with scanty blue reaction product in the cytoplasm and were not labelled as intensely as the hypoglossal nucleus. HRP-positive neurons were in the closed and open parts of the medulla. In the closed medulla, only a few cells of the perihypoglossal nuclei were labelled; in the open medulla, more cells were labelled on both sides. On the right side, 6.0 + 1.0 percent of labelled cells and on the left side, 3.7 + 0.47 percent of labelled cells were present.

Dorsal motor nucleus of vagus.

The dorsal motor nucleus of the vagus of the right side showed a few HRP labelled neurons (Fig.3). The cells were small, cytoplasm was scanty and contained the blue reaction product, and the nucleus and nucleolus were not stained. The intensity of staining was similar to that of perihypoglossal nuclei but less than that of the hypoglossal nucleus. A few labelled neurons were present throughout the medulla. On the left side, no HRP-labelled neuron could be identified. On the right side, 3.2 + 0.35 percent of labelled cells were present.


Staining: Peroxidase activity was demonstrated in tissue sections with three reagents, benzidine, (Kurstak, 1971; Mesulam, 1976a, 1976b, 1978; Mesulam and Rosene, 1979), para phenylene diamine, and pyrocatechol (Hanker et al, 1977) Under the action of HRP and in the presence of hydrogen peroxidase, benzidine was oxidized to a blue reaction product (Kurstak, 1971; Mesulam 1976a, 1976b, 1978; Mesulam and Rosene, 1979), while para phenylene diamine and pyrocatechol were oxidized to a brown reaction product (Hanker et al, 1977).

Whether hypoglossal nerve fibres decussate or not, or whether commissural fibres exist between the hypoglossal nuclei, was a controversy. None of the fibres of the hypoglossal nerve cross the midline, but hypoglossal nuclei are interconnected by commissural fibres (Kuntz, 1945). Chromatolysis and degenerating neurites are shown in the contralateral hypoglossal nucleus in the rat after hypoglossal nerve section (Kirpatrick, 1968).

In the sheep, hypoglossal nerve fibres originate from the hypoglossal nucleus, nucleus ambiguus, nucleus intercalatus and nucleus paramedianis (Welento et al, 1974). Hypoglossal nerve fibres are traced to perihypoglossal nuclei in the rat (Rattus norvegicus albinus) (Cooper, 1982).

Somatic efferent components of the hypoglossal nerve : The hypoglossal nerve is a purely motor nerve (Corbin and Harrison, 1938, Corbin et al, 1939; Barnard, 1940; Weddel, et al, 1940; Blom, 1960). In the rat, motorneurons in the dorsal hypoglossal nucleus innervate the retrusor muscles of the tongue (McClung and Goldberg, 1999). In the chicken, motoneurons innervating the hyolingual muscles were found only in the hypoglossal nucleus (Wang et al, 1996). In the rat, premotor neurons in or around the nucleus of the solitary tract and ventrolateral to the hypoglossal nucleus innervate motoneurons supplying the muscles of the tongue(Dobbins and Feldman, 1995) In guinea pigs, some axons from most caudal neurons of the hypoglossal nucleus emerge in the first cervical nerve and join the hypoglossal nerve in the neck (Mtui and Fitzgerald, 1991). In the caecilian (Amphibia gymnophiona), the occipital nerve emerges through a separate foramen and fuses with spinal nerves 1 and 2 to contribute to the hypoglossal nerve trunk and its nucleus is more similar to spinal nuclei (Schmidt et al, 1996).

General Visceral Efferent Component of the Hypoglossal Nerve:

In the human, a group of preganglionic parasympathetic neurons is present in the hypoglossal nucleus (Schwentker, 1927). In the whale, the hypoglossal nucleus, on the lateral side of its cephalic half, contains smaller general visceral efferent neurons (Wilson, 1934). The lingual ganglia consist of parasympathetic neurons, which receive preganglionic projections from nucleus reticularis parvicellularis in the medulla and are coextensive with salivatory neurons (Chibuzo, et al, 1980). The hypoglossal is derived from ventral-column material, but it is not clearly associated with the vagus phylogenetically (Wake, 1993). The cat's tongue is innervated by fibres, originating in the ipsilateral pterygopalatine ganglion (Ito and Oyagi, 1994). This suggests that this innervation is parasympathetic; probably, the preganglionic fibres are from superior salivatory nucleus. In the frog, the ganglion cells in the lingual branch of the glossopharyngeal nerve are parasympathetic postganglionic cells and the some of the unmyelinated nerve fibres originate from these cells (Inoue and Kitada, 1991); Probably, the preganglionic fibres are from the inferior salivatory nucleus. The salivatory nucleus (pons) also contributes pre-emergence fibres, which supply autonomic ganglia destined for the supply of small arteries in the tongue (O'Reilly ad Fitzgerald 1990). In the rat, the preganglionic parasympathetic neuronal cell bodies, sending projection fibres to the anterior two thirds of the tongue, are distributed mainly in the lateral reticular formation; whereas, those to the posterior one third of the tongue are in the nucleus of the solitary tract and lateral reticular formation; the projection fibres synapsed with the intralingual ganglion cells (Tsumori et al, 1996). In the hamster, the hypoglossal nerve contains sympathetic component from the superior cervical ganglion, which may be involved in regulation of the autonomic function of the tongue (Tseng et al, 2001). The nerve cells on the hypoglossal nerve resemble the cells in the inferior ganglion of the vagus nerve and are always observed within the communicating rami between the nerve and ganglion; possibly, these cells migrate from the ganglion of the vegus to the hypoglossal nerve for proprioceptive innervation of the tongue (Wozniak and Young, 1968). Probably the ganglion cells in the tongue also migrate from the neural crest, along the vagus, its communications, and hypoglossal nerve to the tongue.

The demonstration, in the present study, of a greater number of labelled neurons in the hypoglossal nucleus on the side of HRP delivery, and lesser number on the opposite side, establishes that each hypoglossal nerve contains axons from both the right and left hypoglossal nuclei. In the rat, injection of HRP into the geniohyoid muscle demonstrates labelled neurons in the perihypoglossal nuclei of both sides (Watkins, 1978). Similarly, in the present study, occurrence of HRP labelled neurons in both- sided perihypoglossal nuclei, more in the side of HRP delivery, has shown that the hypoglossal nerve contains axons from both the right and left perihypoglossal nuclei. Hypoglossal nerve axotomy in the sheep demonstrates chromatolysis of neurons in the same-sided nucleus ambiguus (Welento et al, 1974). Though workers drew attention to a few sources of parasympathetic efferent fibres of the hypoglossal nerve, the dorsal motor nucleus of vagus has never been mentioned. In the present study, the presence of a few labelled neurons in the dorsal motor nucleus of the vagus, only on the side of axotomy and HRP delivery, suggests that the hypoglossal nerve has axons from the dorsal motor nucleus of the vagus and that the axons are from the nucleus of the same side only.

During the development of the motor nuclei, the neuroblasts of the myelencephalic basal plate migrate dorsolaterally to form the dorsal motor vagal nucleus and ventrolaterally to form the ventral motor vagal nucleus (nucleus ambiguous) and remain close to the median sulcus to form the hypoglossal nucleus (Macchi et al, 2002). Probably, some of the neuroblasts, to the dorsal motor vagal nucleus, migrate to the tongue along the hypoglossal nerve and become the lingual ganglion cells.


The present study, with the HRP retrograde tracing technique on the right hypoglossal nerve, has shown that the constituent somatomotor fibres of the hypoglossal nerve originate bilaterally from the hypoglossal nuclei and bilaterally from perihypoglossal nuclei and the constituent visceromotor fibres originate monolaterally from the ipsilateral dorsal motor nucleus of the vagus. This neural pattern is demonstrated and reported for the first time in the monkey.


The author thanks Dr. M. Muthu and Dr. Leela Rajendran for guidance in this work.


  1. Barnard, J.W. (1940): The hypoglossal complex of vertebrates. Journal of Comparative Neurology 72: 489-524.
  2. Blom, S. (1960) : Afferent influences on tongue muscle activity. A morphological and physiological study in the cat. Acta Physiology Scandinavia 49 : 1-97.
  3. Boyd, M.D. (1941) : The sensory component of the hypoglossal nerve in the rabbit. Journal of Anatomy 75 : 330345.
  4. Chhatri, D.K. and Berke, D.S. (1997); Ansa cervicalis nerve. Laryngoscope 107 :1366-1372.
  5. Chibuzo, G.A. Cummings, J.F. and Evans, H.E. (1980) : Autonomic innervation of the tongue : a horseradish peroxidase study in the dog. Journal of Autonomic Nervous System 2 : 117-129.
  6. Cooper, M.H. (1982): Hypoglossal fibres to perihypoglossal nuclei in rat (Rattus Norvegicus albinus). Anatomical Record 202 : (Abstract) : 35A- 36A.
  7. Corbin, K.B. and Harrison, F. (1938) : Further studies on tongue innervation. Proceedings of the Society of Experimental Biological Medicine 38 : 308.
  8. Corbin, K.B. Lhamon, W.T. and Petit, D.W. (1939) : Peripheral and central connections of the upper cervical dorsal root ganglia in the rhesus monkey. Journal of Comparative Neurology 66 : 405- 414.
  9. Dobbins, E.G. and Feldman, J.L. (1995) : Differential innervation of protruder and retractor muscles of the tongue in rat. Journal of Comparative Neurology 357 : 376-394.
  10. Hanker, J.S. Yatex, P.E., Metz, C.B. and Rustioni, A (1977) : A new specific, sensitive and noncarcinogenic reagent for the demonstration of horseradish peroxidase (HRP). Journal of Histochemistry 9 : 789-792.
  11. Inoue, K. and Kitada, Y. (1991) : Parasympathetic postganglionic cells in the glossopharyngeal nerve trunk and their relationship to unmyelinated nerve fibres in the fungiform papillae of the frog. Anatomical Record 230 : 131-135.
  12. Ito, J. and Oyagy, S. (1994) : Determination of the origin of autonomic nerves of the tongue using horseradish peroxidase as tracer. European Archives of Otorhinolaryngology 251 : 117-118.
  13. Kirpatrick, J.B. (1968) : Chromatolysis in the hypoglossal nucleus of the rat. An electron microscopic analysis. Journal of Comparative Neurology 132 : 189 - 212.
  14. Kuntz, A. (1945) : Components and distribution of the nerves of the parotid and submandibular glands. Journal of Comparative Neurology 85 : 21 - 32.
  15. Kurstak, E. (1971) : Immunoperoxidase technique localization of viral antigen in cells. Methods in Virology 5 : 423.
  16. Macchi, V., Snenghi, R., de Caro, R. and Parenti, A. (2002) : Monolateral hypoplasia of the motor vagal nuclei in a case of sudden infant death syndrome. Journal of Anatomy 200 : 195-198.
  17. Mesulam, M.M. (1976a): The blue reaction product in horseradish peroxidase. Neurochemistry incubation parameters and visibility. Journal of Histochemistry and Cytochemistry 24 : 1273-1280.
  18. Mesulam, M.M. (1976b): A horseradish peroxidase method for identification of the efferents of acetylcholinesterase containing neurons. Journal of Histochemistry and Cytochemistry 24 : 1281-1286.
  19. Mesulam, M.M. (1978): Tetramethyl benzidine for horseradish peroxidase neurochemistry. A noncarcinogenic blue reaction product with superior sensitivity for visualizing neural afferents and efferents. Journal of Histochemistry and Cytochemistry 26 : 106-117.
  20. Mesulam, M.M. Rosene DL (1979) : Sensitivity in horseradish peroxidase neurochemistry. A comparative and quantitative study of nine methods. Journal of Histochemistry and Cytochemistry 27 : 763-773.
  21. McClung, J.R. and Goldberg, S.J. (1999) : Organization of motoneurons in the dorsal hypoglossal nucleus that innervate the retrusor muscles of the tongue in the rat. Anatomical Record 254 : 222-230.
  22. Mtui, E.P. and Fitzgerald, M.J. (1991) : Experimental histological evidence for a dual motor pathway from the hypoglossal nucleus to lingual muscles in the guinea pig. Archives of Oral Biology 36 : 319-322.
  23. O' Reilly, P.M.R. and Fitzgerald, M.J.T. (1990) : Fibre composition of the hypoglossal nerve in the rat. Journal of Anatomy 172 : 227-243.
  24. Rosene, D.L. and Mesulam, M.M. (1978) : Fixation variables in horseradish peroxidase neurochemistry. The effect of fixation time and perfusion procedures upon enzyme activity. Journal of Histochemistry and Cytochemistry 26 : 28-39.
  25. Schmidt, A., Wake, D.B. and Wake, M.H. (1996) : Motor nuclei of nerves innervating the tongue and hypoglossal musculature in a caecilian (Amphibia gymnophiona), as revealed by HRP transport, Journal of Comparative Neurology 370 : 342-349.
  26. Schwentker, E.F. (1927) : A group of small cells in the hypoglossal nucleus of man. Anatomical Record 35 : 345358. J. Anat. Soc. India 52(1) 46-50 (2003)
  27. Tseng, C.Y., Lue, J.H., Lee, S.H., Wen, C.Y. and Shieh, J.Y. (2001) : Evidence of neuroanatomical connection between the superior cervical ganglion and hypoglossal nerve in the hamster as revealed by tract-tracing and degeneration methods. Journal of Anatomy 198 : 407-421.
  28. Tsumori,T., Ando, A. and Yasui, Y. (1996) : A light and electron microscope study of the connections between the preganglionic fibres and the intralingual ganglion cells in the rat. Anatomy and Embryology (Berl)194 : 559-568.
  29. Wake, D.B. (1993) : Brainstem organization and branchiomeric nerves. Acta Anatomica (Basel) 148 : 124-131.
  30. Watkins, D.W. (1978) : Hypoglossal nucleus. Localizaion of motoneuronal pool. Anatomical Record 190 (Abstract) : 576-577.
  31. Wang, J., Watanabe, T., Suzuki, M., Ohmori, Y. and Naito, J. (1996) : Muscle representation within the hypoglossal nucleus of the chicken studied by means of horseradish peroxidase. Anatomy Histology and Embryology 25 : 277282.
  32. Weddel, G. Harpman, J.A. Lambley, D.G. and Young, L. (1940) : The innervation of the musculature of the tongue. Journal of Anatomy 74 : 255-267
  33. Welento, J. and Flieger, S. (1974) : Experimental investigations of the the nerve centres of the hypoglossal nerve in the sheep. Pol Arch Wetet 15 : 869.
  34. Williams, P.L; Bannister, L.H.; Berry. M-M; Collins, P; Dyson, M; Dussek, J.E; Ferguson, M.W.J. Gray's Anatomy In : Nervous System. 38th Edn. Churchill Livingestone, New York : pp 1256-7 (1995)
  35. Wilson, R.B. (1934) : The anatomy of the brain of the whale (Balaenoptera sullfurae). Journal of Comparative Neurology 58: 419.
  36. Wozniak, W. and Young, P.A. (1968) : Nerve cells in the extracranial portion of the hypoglossal nerve in the human fetus. Anatomical Record 162 : 517-522.

Missing Image


Transverse section of the medulla oblongata. V-central canal; MFR-median fibrous raphe; HRP labelled neurons (arrow) in the right side hypoglossal nucleus; a few neurons on the contralateral left hypoglossal nucleus. HRP 80X.

Missing Image


Right hypoglossal nucleus. Blue reaction product in the cytoplasm (arrow). HRP 80X.

Missing Image


Transverse section of the medulla oblongata.Central canal is present; Right perihypoglossal nuclei (medial arrow); dorsal motor nucleus of the vagus (lateral arrow). HRP 80 X.

Access free medical resources from Wiley-Blackwell now!

About Indmedica - Conditions of Usage - Advertise On Indmedica - Contact Us

Copyright © 2005 Indmedica