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The central projections of the great auricular nerve primary afferent fibers — an HRP transganglionic tracing method
Brain Research, 445 (1988) 205-2 |0 Elsevier
205
BRE 13409
Research Reports
The central projections of the great auricular nerve primary afferent fibers an HRP transganglionic tracing method Dayong Liu and Yaomin Hu Department of Anatomy, the First Military Medical College, Guangzhou (People's Republic of China) (Accepted 15 September 1987)
Key words: Horseradish peroxidase (HRP); Great auricular nerve; Afferent fiber; Transganglionic transport
A study of the central distribution of the primary afferent fibers of the great auricular nerve (GAN) was made in 18 iabbits by means of transganglionic transport of horseradish peroxidase (HRP). HRP applied to the cut central end of the GAN was detected ipsilaterally in the dorsal root ganglion cells (segments C.,-C3) and the superior cervical ganglion cells. The transganglionically labeled fibers were seen in the dorsal column of the upper 4 cervical segments and in the cranial nerve nuclei of the medulla oblongata. The afferent projections were rather strong in the regions of laminae I-V of C_,, the caudal subnucleus of the nucleus of the spinal tract of the trigeminal nerve (NVSpc), the solitary nucleus (SN), the medial and lateral cuneate nuclei, etc. The results showed that the primary afferent impulses of the GAN and the peripheral nerves which supply the head, face, trunk and viscera might converge on the upper cervical cord, the NVSpc and the SN, and play a certain role of modulation on the transmission of somaticovisceral sensations, especially pain. INTRODUCTION The great auricular nerve ( G A N ) is the largest of the ascending branches of the cervical plexus. It arises from the second and third cervical nerves, supplies the skin of the face over the parotid gland and the mastoid process and on the back of the auricle. The branch to the concha of the auricle of the G A N is distributed to the cavity and cymba of concha, which are areas specified for the treatment of diseases of chest and abdomen with ear acupuncture 3. The present experiments were undertaken to examine the central projections of primary afferents of the G A N and give anatomical evidence for explaining the clinical pl~enomena that ear acupuncture and ear root anesthesia can provide effective analgesia and trigeminal neuralgia may be healed when the G A N is sectioned, etc 6"7. G A N afferent projections to the upper cervical cord and the medulla obiongata were labeled by means of the technique of transganglionic transport
of horseradish peroxidase (HRP). This technique has been used previously in the literature 4. MATERIALS AND METHODS Experiments were carried out on 20 rabbits, 1.5-3.0 kg in body weight, anesthetized with 30% urethane solution (1.2/mg, i.v.). Under general anesthesia, a skin incision was made in the region of sternocieidomastoideus. The skin and fasciae were separated to expose the right G A N which were traced carefully to the region of the ear root, where the G A N was cut. A piece of film was placed between the nerve and underlying tissue to prevent the diffusion of HRP. The cut central end of the G A N was bathed in a pipette filled with 30% H R P in physiological saline for 3 - 5 h in 18 cases. In two control cases, the H R P was applied in the area of the exposed but intact G A N . After 72 h, the animals were reanesthetized and perfused intracardially with 500 ml of normal sa!in, followed bv 600 ml of 1% para-
Correspondence: D. Liu, Department of Anatomy, The First Military Medical College, Guangzhou, The People's Republic of China. 0006-8993/88/$03.50 © 1988 Elsevier Science Publishers B.V. (Biomedical Division)
206 formaldehyde and 1.25% glutaraldehyde in 0.1 M phosphate buffer (pH 7.4), followed by 500 ml of 5% sucrose in 0.1 M phosphate buffer at 4 °C. The brainstem, cervical spinal cord and superior cervical ganglia were removed and transferred to phosphate buffer containing 5% sucrose for 15-48 h at 4 °C. Brainstems, cervical spinal cord and ganglia were cut on a freezing microtome to make 40-/xm sections. Tissue sections were reacted with o-dianisidine by the Edwards method ~, but the reaction time was 4-5 times longer than that of the original method (at 4 °C). RESULTS HRP-labeled terminal or preterminal fibers were identified under the light microscope. They often appeared as green granules of various sizes and different shapes. The granules in some fields were uniform and fine, while others appeared as a string of beads of different sizes. The space between beads was linked
by finer granules. The anterograde labeling fibers should be recognized in accordance with the above characteristics.
Ganglia A great number of labeled cells were observed in the ipsilateral dorsal root ganglia (DRG) of segments C2 and C3 in all 18 animals. Labeled cells appeared as large round cells, 20-50 gm in diameter. The cytoplasm of the labeled cells was nearly filled with the green granules. The cell processes appeared as a chain of finer granules arranged in a row (Fig. 1A). The labeled cells in DRG are obviously more numerous in segment C~ than in segment C3. This is consistent with the composition of the GAN which consists of the dorsal branches of C2 and C3 nerves, but predominantly those of the C2 nerve. A small number of HRP-labeled cells were identified in the ipsila.teral superior cervical ganglia (Fig. 1B), and were frequently ovoid or fusiform in shape and 15 x 50 pm in size.
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Fig. 1. Parasagittal sections of a C, dorsal root ganglion (A) and superior cervical ganglion (B)showing well-labeled ganglion cellsand their axons. Bar = 5(lllm.
Fig. 2. The distribution of central afferent projections of the great auricular nerve at the upper 4 cervical segments of the spinal cord. up, upper half of each segment.
207
Dorsal horns of upper cervical cord Transganglionically labeled fibers entered the ipsilateral dorsal funiculus and horns of segments C 2 and C a along the C2 and C3 dorsal root fibers, from which the labeled fibers could be traced to ascend to dorsal horn of the Ct segment and descend to the C4 segment (Fig. 2). C2. In the C2 segment, labeled fibers of the dorsal
•
root entered largely the dorsolateral part of the fasciculus cuneatus and a few of the labeled fibers entered the lateral half of Lissauer's tract. A few bundles arising from the fasciculus cuneatus passed through the ipsilateral dorsal horn into the lateral part of laminae I - V which occupied about threequarters of the whole gelatinous substance (GS, Fig. 3A, a).
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Fig. 3. Transverse sections of C_, spinal cord (A, B) showing HRP-labeled fibers and terminal fibers of dorsal root, fasciculus cuneatus and dorsal horn: sections of C I spinal cord (C. D) showed the labeled ascending fibers from the fasciculus cuneatus converged at the medial margin of the juncture of head and neck of the dorsal horn. Bar = 50!~m.
208 C~. At the C3 level, the labeled terminal fibers were similarly distributed as at the C2 segment, ending predominantly within laminae II-IV which occupied about one half of the whole GS. Ct. The labeled ascending fibers from the fasciculus cuneatus converged at the medial margin of the juncture of the head and neck of the dorsal horn, and then extended to the medial half of GS, in laminae II and III. At the inferior portion of the C~ segment, labeled terminal fibers of bundle-like shape were observed in the medial part of the neck of the dorsal horn which is equivalent to laminae V and VI (Fig. 3C, D).
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.
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Medulla oblongata In 10 of the 18 animals, transganglionically labeled terminal and preterminal fibers existed in the medial and lateral cuneate nuclei (Cum and Cul), the caudal and rostral subnuclei of the nucleus of spinal tract of the trigeminai nerve (NVSpc and NVSpo), the solitary nucleus (SN), etc.
Transverse section through the intermediate portion of the decussation of pyramids (Fig. 4A). Labeled terminal fibers were found in the dorsal portion of fasciculus cuneatus, from which they entered the Cure in the form of several bundles and extended to the dorsomedial portion of the NVSpc, mainly in the marginal layer and GS.
Transverse section through the decussation of the lemniscus (Fig. 4B). At this level, the labeled termi-
.,,._..,a.
sN
C4. The labeled descending fibers in the lateral part of the fasciculus cuneatus entered the lateral half of the ipsilateral GS. These fibers were limited in number and scope.
NVSpc
':.-.....-'
:?..::'.':
nals in the fasciculus cuneatus decreased and in the Cum (Fig. 5A) increased in number, and extended into the SN (Fig. 5C), predominantly within the dorsal and interstitial subnuclei of the SN 2. A few HRPlabeled fibers were also found in the dorsomedial and ventrolateral portion of the marginal layer and GS of the NVSpc (Fig. 5B).
Transverse section through the caudal portion of fourth ventricle (Fig. 4C). HRP-labeled terminal fi-
.. ?.~::-. . .
NVSp¢
Fig. 4. The distribution of central afferent projections of the great auricular nerve at the medulla oblongata. A: transverse section through the intermediate portion of the deeussation of pyramid. B: transverse section through the deeussation of lemniscus. C: transverse section through the caudal portion of fourth ventricle. Cul, lateral cuneate nucleus; Cure, medial cuneate nucleus; Gr, nucleus gracilis; NVSpc, caudal subnucleus of the nucleus of spinal tract of the trigeminal nerve (z, marginal layer; g, layer of gelatinous substance; me, magnieellular
layer); NVSpo, rostral subnucleus of the nucleus of spinal tract of the trigeminai nerve; Ts, solitary tract; SN, solitary nucleus; ni, interstitial subnucleus of the solitary nucleus; Rpc, reticular parvicellular nucleus; Rd, dorsai subnucleus of the reticular nucleus; Rv, ventral subnucleus of the reticular nucleus.
bers were observed in the ventrolateral part of the Cul, dorsomedial and ventrolateral parts of the NVSpo, besides in the Cum and SN. One animal had preterminal fibers, which were weeping willowshaped, in the medial portion of the reticular parvicellular nucleus of the medulla oblongata (Fig. 5D). DISCUSSION
It was noted earlier that the primary afferent fibers from regions of face, neck and viscera project onto the upper cervical cord through different peripheral nerves. In the past few years, it was reported that after cutting all three branches of the trigeminal nerve, the descending degenerated fibers were seen in laminae I - V of the dorsal horns of the upper third cervical segment, and the activity of the acid phosphatase was lost in the GS of the Cl and C 2 segments 8. After
209
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.
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Fig. 5. Transverse sections of the medulla oblongata showing HRP-labeled terminal or preterminal fibers at the fasciculuscuneatus and Cum (A), the NVSpc (B), the SN (C) and the reticular parvicellularnucleus (D). Bar = 501~m
the destruction of the NVSpc, the degenerated fibers were found in the ipsilateral Lissauer's tract and laminae I - I I I of the C]-C3 segments; the primary afferent fibers of the vagus nerve, glossopharyngeal nerve and facial nerve entered the dorsal horns of the C n and C 2 segments. Shriver et al. 5 also reported that after the second cervical dorsal root was sectioned, the degenerated fibers t,.rminated primarily in the lateral regions of laminae Ill and IV of the C 2 segment and the descending C 2 root fibers in the lateral part of the fasciculus cuneatus could be found at the C a and C4 spinal segments 5. Zhu et al. found that after the GAN was cut, areas without acid phosphatase activi-
ty were observed in the GS of the upper 4 cervical segments of the spinal cord s . The present findings are in accord with the above-mentioned reports in the projection of segments of the upper cervical cord. This study indicates that the fine fibers of the C, and C3 dorsal roots passed in the fasciculus cuneatus and lateral border of Lissauer's tract and travelled through the medial and lateral two pathways to terminate in the GS and proper nucleus of the dorsal horn. In general, it is believed that Lissauer's tract is the afferent pathway of pain and temperature sensory impulses. Nociceptive-specific neurons in dorsal horn are concentrated in the marginal layer (lamina I) and its ad-
210 jacent outer zone of GS (lamina II); wide-dynamicrange neurons, named by Yokota, were found not only in the superficial layers but also in the proper nucleus (laminae IV-VI) 8. It is generally agreed that the NVSpc is a relay nucleus of pain and temperature. The SN receives impulses from gustatory and general visceral sensation. In the literature, it is reported that following vagal and glossopharyngeal tractotomy, the primary afferent fibers of the Xth and IXth cranial nerves were seen to end in the NVSpc and SN; after the upper 4 cervical DRG were sectioned, the degenerated fibers were seen in the lateral part of the NVSpc; after the second cervical DRG was cut, a few degenerated fibers were seen to terminate in the SN and ventro!ateral parts of the magnoceilular division of the trigeminal spinal nucleus 5.7.8. The present study indicated that the primary afferent fibers of GAN terminate not only in the upper 4 cervical segments, but also ascend directly through the dorsal funieulus of the cervical cord to the ipsilateral SN, NVSpo and the dorsomedial and ventrolateral portions of the GS of the NVSpc, where they may well converge with afferent fibers from the head, face, trunk and viscera, etc. The primary afferent fibers of the GAN project onto the ipsilateral Cum and Cul. In general, the proprioceptive sensation from the upper half of the body i'; converged to the nucleus cuneatus. The proprioceptive impulses from the upper limb and neck, after relaying in the Cul via the cuneocerebellar tract, project onto the ipsilateral cerebellum. These associations probably result in better analgesia on the upper
half of the body using acupuncture anesthesia. We found that the primary afferent fibers of the GAN from one animal project onto the ipsilaterai reticular parvicellular nucleus of the medulla oblongata. Shriver et al. had found that in two cases the degenerated fibers were seen at the same place following C2 dorsal root section 5. The connectivity in the reticular formation of the medulla oblongata is very complicated where various sensations are converged. Electrophysiological study shows that the reticular formation of the medulla oblongata has played some roles in inhibiting visceralgesia. Labeled cells were seen in ipsilateral superior cervical ganglia, which indicated that the GAN contains sympathetic fibers. This study demonstrates that the primary afferent fibers of the GAN and other peripheral nerves may well converge on the upper cervical cord, the nucleus of the spinal tract of the trigeminal nerve and the solitary nucleus of the medulla oblongata, which may be regarded as an anatomical basis for explah~ing the clinical phenomena that trigeminal neuralgia may be healed when the GAN is sectioned, the pain in the area of the upper neck may be referred to regions of the head and headache may be also referred to regions of the upper neck, etc.
REFERENCES
rol., 201 (1981) 415-440. 5 Shriver, J.E., Stein, B.M. and Carpenter, M.B,, Central projections of spinal dorsal roots in the monkey. I. Cervical and upper thoracic dorsal roots, Am. J. Anat., 123 (1968) 27-74. 6 Taren, J.A. and Kahn, E.A., Anatomic pathways related to pain in face and neck, J. Neurosurg., 19 (1962) 116-121. 7 Yokota, T., Noeiceptive neurons in the dorsal horn of the spinal cord and in the spinal tract nucleus of the trigeminal nerve, Adv. Neurol. Sci. (Jpn.). 26 (1982) 843-856. 8 Zhu, P., Wu, H. and Xu, H., The connections of the trigeminal, facial, vagus nerves and cutaneous branches of the cervical plexus with the substantia gelatinosa of the rat, Acta Anat. Sin. (Chin.), 14 (1983) 278-282.
1 Edwards, S.B., Ginsburgh, C.L., Henkel, C.K. and Stein, B.E., Sources of subcortical projections to the superior colliculus in the cat, J. Comp. Neurol., 184 (1979) 309-330. 2 Kalia, M. and Sullivan, J.M., Brainstem projections of sensory and motor components of the vagus nerve in the rat, J. Comp. Neurol., 211 (1982)248-264. 3 Lei, Q., Nerves and arteries of the external ear, Acta Anat. Sin. (Chin.), 6 (1963) 29-37. 4 Morgan,C., Nadelhaft, I. and de Groat, W.C., The distribution of visceral primary afferents from the pelvic nerve to Lissauer's tract and the spinal gray matter and its relationship to the sacral parasympathetic nucleus, J. Comp. Neu-
ACKNOWLEDGEMENTS The authors wish to thank Prof. Xu Qian for his help in preparing this article.
205
BRE 13409
Research Reports
The central projections of the great auricular nerve primary afferent fibers an HRP transganglionic tracing method Dayong Liu and Yaomin Hu Department of Anatomy, the First Military Medical College, Guangzhou (People's Republic of China) (Accepted 15 September 1987)
Key words: Horseradish peroxidase (HRP); Great auricular nerve; Afferent fiber; Transganglionic transport
A study of the central distribution of the primary afferent fibers of the great auricular nerve (GAN) was made in 18 iabbits by means of transganglionic transport of horseradish peroxidase (HRP). HRP applied to the cut central end of the GAN was detected ipsilaterally in the dorsal root ganglion cells (segments C.,-C3) and the superior cervical ganglion cells. The transganglionically labeled fibers were seen in the dorsal column of the upper 4 cervical segments and in the cranial nerve nuclei of the medulla oblongata. The afferent projections were rather strong in the regions of laminae I-V of C_,, the caudal subnucleus of the nucleus of the spinal tract of the trigeminal nerve (NVSpc), the solitary nucleus (SN), the medial and lateral cuneate nuclei, etc. The results showed that the primary afferent impulses of the GAN and the peripheral nerves which supply the head, face, trunk and viscera might converge on the upper cervical cord, the NVSpc and the SN, and play a certain role of modulation on the transmission of somaticovisceral sensations, especially pain. INTRODUCTION The great auricular nerve ( G A N ) is the largest of the ascending branches of the cervical plexus. It arises from the second and third cervical nerves, supplies the skin of the face over the parotid gland and the mastoid process and on the back of the auricle. The branch to the concha of the auricle of the G A N is distributed to the cavity and cymba of concha, which are areas specified for the treatment of diseases of chest and abdomen with ear acupuncture 3. The present experiments were undertaken to examine the central projections of primary afferents of the G A N and give anatomical evidence for explaining the clinical pl~enomena that ear acupuncture and ear root anesthesia can provide effective analgesia and trigeminal neuralgia may be healed when the G A N is sectioned, etc 6"7. G A N afferent projections to the upper cervical cord and the medulla obiongata were labeled by means of the technique of transganglionic transport
of horseradish peroxidase (HRP). This technique has been used previously in the literature 4. MATERIALS AND METHODS Experiments were carried out on 20 rabbits, 1.5-3.0 kg in body weight, anesthetized with 30% urethane solution (1.2/mg, i.v.). Under general anesthesia, a skin incision was made in the region of sternocieidomastoideus. The skin and fasciae were separated to expose the right G A N which were traced carefully to the region of the ear root, where the G A N was cut. A piece of film was placed between the nerve and underlying tissue to prevent the diffusion of HRP. The cut central end of the G A N was bathed in a pipette filled with 30% H R P in physiological saline for 3 - 5 h in 18 cases. In two control cases, the H R P was applied in the area of the exposed but intact G A N . After 72 h, the animals were reanesthetized and perfused intracardially with 500 ml of normal sa!in, followed bv 600 ml of 1% para-
Correspondence: D. Liu, Department of Anatomy, The First Military Medical College, Guangzhou, The People's Republic of China. 0006-8993/88/$03.50 © 1988 Elsevier Science Publishers B.V. (Biomedical Division)
206 formaldehyde and 1.25% glutaraldehyde in 0.1 M phosphate buffer (pH 7.4), followed by 500 ml of 5% sucrose in 0.1 M phosphate buffer at 4 °C. The brainstem, cervical spinal cord and superior cervical ganglia were removed and transferred to phosphate buffer containing 5% sucrose for 15-48 h at 4 °C. Brainstems, cervical spinal cord and ganglia were cut on a freezing microtome to make 40-/xm sections. Tissue sections were reacted with o-dianisidine by the Edwards method ~, but the reaction time was 4-5 times longer than that of the original method (at 4 °C). RESULTS HRP-labeled terminal or preterminal fibers were identified under the light microscope. They often appeared as green granules of various sizes and different shapes. The granules in some fields were uniform and fine, while others appeared as a string of beads of different sizes. The space between beads was linked
by finer granules. The anterograde labeling fibers should be recognized in accordance with the above characteristics.
Ganglia A great number of labeled cells were observed in the ipsilateral dorsal root ganglia (DRG) of segments C2 and C3 in all 18 animals. Labeled cells appeared as large round cells, 20-50 gm in diameter. The cytoplasm of the labeled cells was nearly filled with the green granules. The cell processes appeared as a chain of finer granules arranged in a row (Fig. 1A). The labeled cells in DRG are obviously more numerous in segment C~ than in segment C3. This is consistent with the composition of the GAN which consists of the dorsal branches of C2 and C3 nerves, but predominantly those of the C2 nerve. A small number of HRP-labeled cells were identified in the ipsila.teral superior cervical ganglia (Fig. 1B), and were frequently ovoid or fusiform in shape and 15 x 50 pm in size.
Cl
up o
O
--
~,:,
:
~tI
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, I ~
O
C~ O
1, •~,b "
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Fig. 1. Parasagittal sections of a C, dorsal root ganglion (A) and superior cervical ganglion (B)showing well-labeled ganglion cellsand their axons. Bar = 5(lllm.
Fig. 2. The distribution of central afferent projections of the great auricular nerve at the upper 4 cervical segments of the spinal cord. up, upper half of each segment.
207
Dorsal horns of upper cervical cord Transganglionically labeled fibers entered the ipsilateral dorsal funiculus and horns of segments C 2 and C a along the C2 and C3 dorsal root fibers, from which the labeled fibers could be traced to ascend to dorsal horn of the Ct segment and descend to the C4 segment (Fig. 2). C2. In the C2 segment, labeled fibers of the dorsal
•
root entered largely the dorsolateral part of the fasciculus cuneatus and a few of the labeled fibers entered the lateral half of Lissauer's tract. A few bundles arising from the fasciculus cuneatus passed through the ipsilateral dorsal horn into the lateral part of laminae I - V which occupied about threequarters of the whole gelatinous substance (GS, Fig. 3A, a).
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Fig. 3. Transverse sections of C_, spinal cord (A, B) showing HRP-labeled fibers and terminal fibers of dorsal root, fasciculus cuneatus and dorsal horn: sections of C I spinal cord (C. D) showed the labeled ascending fibers from the fasciculus cuneatus converged at the medial margin of the juncture of head and neck of the dorsal horn. Bar = 50!~m.
208 C~. At the C3 level, the labeled terminal fibers were similarly distributed as at the C2 segment, ending predominantly within laminae II-IV which occupied about one half of the whole GS. Ct. The labeled ascending fibers from the fasciculus cuneatus converged at the medial margin of the juncture of the head and neck of the dorsal horn, and then extended to the medial half of GS, in laminae II and III. At the inferior portion of the C~ segment, labeled terminal fibers of bundle-like shape were observed in the medial part of the neck of the dorsal horn which is equivalent to laminae V and VI (Fig. 3C, D).
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.
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C~
Medulla oblongata In 10 of the 18 animals, transganglionically labeled terminal and preterminal fibers existed in the medial and lateral cuneate nuclei (Cum and Cul), the caudal and rostral subnuclei of the nucleus of spinal tract of the trigeminai nerve (NVSpc and NVSpo), the solitary nucleus (SN), etc.
Transverse section through the intermediate portion of the decussation of pyramids (Fig. 4A). Labeled terminal fibers were found in the dorsal portion of fasciculus cuneatus, from which they entered the Cure in the form of several bundles and extended to the dorsomedial portion of the NVSpc, mainly in the marginal layer and GS.
Transverse section through the decussation of the lemniscus (Fig. 4B). At this level, the labeled termi-
.,,._..,a.
sN
C4. The labeled descending fibers in the lateral part of the fasciculus cuneatus entered the lateral half of the ipsilateral GS. These fibers were limited in number and scope.
NVSpc
':.-.....-'
:?..::'.':
nals in the fasciculus cuneatus decreased and in the Cum (Fig. 5A) increased in number, and extended into the SN (Fig. 5C), predominantly within the dorsal and interstitial subnuclei of the SN 2. A few HRPlabeled fibers were also found in the dorsomedial and ventrolateral portion of the marginal layer and GS of the NVSpc (Fig. 5B).
Transverse section through the caudal portion of fourth ventricle (Fig. 4C). HRP-labeled terminal fi-
.. ?.~::-. . .
NVSp¢
Fig. 4. The distribution of central afferent projections of the great auricular nerve at the medulla oblongata. A: transverse section through the intermediate portion of the deeussation of pyramid. B: transverse section through the deeussation of lemniscus. C: transverse section through the caudal portion of fourth ventricle. Cul, lateral cuneate nucleus; Cure, medial cuneate nucleus; Gr, nucleus gracilis; NVSpc, caudal subnucleus of the nucleus of spinal tract of the trigeminal nerve (z, marginal layer; g, layer of gelatinous substance; me, magnieellular
layer); NVSpo, rostral subnucleus of the nucleus of spinal tract of the trigeminai nerve; Ts, solitary tract; SN, solitary nucleus; ni, interstitial subnucleus of the solitary nucleus; Rpc, reticular parvicellular nucleus; Rd, dorsai subnucleus of the reticular nucleus; Rv, ventral subnucleus of the reticular nucleus.
bers were observed in the ventrolateral part of the Cul, dorsomedial and ventrolateral parts of the NVSpo, besides in the Cum and SN. One animal had preterminal fibers, which were weeping willowshaped, in the medial portion of the reticular parvicellular nucleus of the medulla oblongata (Fig. 5D). DISCUSSION
It was noted earlier that the primary afferent fibers from regions of face, neck and viscera project onto the upper cervical cord through different peripheral nerves. In the past few years, it was reported that after cutting all three branches of the trigeminal nerve, the descending degenerated fibers were seen in laminae I - V of the dorsal horns of the upper third cervical segment, and the activity of the acid phosphatase was lost in the GS of the Cl and C 2 segments 8. After
209
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.
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Fig. 5. Transverse sections of the medulla oblongata showing HRP-labeled terminal or preterminal fibers at the fasciculuscuneatus and Cum (A), the NVSpc (B), the SN (C) and the reticular parvicellularnucleus (D). Bar = 501~m
the destruction of the NVSpc, the degenerated fibers were found in the ipsilateral Lissauer's tract and laminae I - I I I of the C]-C3 segments; the primary afferent fibers of the vagus nerve, glossopharyngeal nerve and facial nerve entered the dorsal horns of the C n and C 2 segments. Shriver et al. 5 also reported that after the second cervical dorsal root was sectioned, the degenerated fibers t,.rminated primarily in the lateral regions of laminae Ill and IV of the C 2 segment and the descending C 2 root fibers in the lateral part of the fasciculus cuneatus could be found at the C a and C4 spinal segments 5. Zhu et al. found that after the GAN was cut, areas without acid phosphatase activi-
ty were observed in the GS of the upper 4 cervical segments of the spinal cord s . The present findings are in accord with the above-mentioned reports in the projection of segments of the upper cervical cord. This study indicates that the fine fibers of the C, and C3 dorsal roots passed in the fasciculus cuneatus and lateral border of Lissauer's tract and travelled through the medial and lateral two pathways to terminate in the GS and proper nucleus of the dorsal horn. In general, it is believed that Lissauer's tract is the afferent pathway of pain and temperature sensory impulses. Nociceptive-specific neurons in dorsal horn are concentrated in the marginal layer (lamina I) and its ad-
210 jacent outer zone of GS (lamina II); wide-dynamicrange neurons, named by Yokota, were found not only in the superficial layers but also in the proper nucleus (laminae IV-VI) 8. It is generally agreed that the NVSpc is a relay nucleus of pain and temperature. The SN receives impulses from gustatory and general visceral sensation. In the literature, it is reported that following vagal and glossopharyngeal tractotomy, the primary afferent fibers of the Xth and IXth cranial nerves were seen to end in the NVSpc and SN; after the upper 4 cervical DRG were sectioned, the degenerated fibers were seen in the lateral part of the NVSpc; after the second cervical DRG was cut, a few degenerated fibers were seen to terminate in the SN and ventro!ateral parts of the magnoceilular division of the trigeminal spinal nucleus 5.7.8. The present study indicated that the primary afferent fibers of GAN terminate not only in the upper 4 cervical segments, but also ascend directly through the dorsal funieulus of the cervical cord to the ipsilateral SN, NVSpo and the dorsomedial and ventrolateral portions of the GS of the NVSpc, where they may well converge with afferent fibers from the head, face, trunk and viscera, etc. The primary afferent fibers of the GAN project onto the ipsilateral Cum and Cul. In general, the proprioceptive sensation from the upper half of the body i'; converged to the nucleus cuneatus. The proprioceptive impulses from the upper limb and neck, after relaying in the Cul via the cuneocerebellar tract, project onto the ipsilateral cerebellum. These associations probably result in better analgesia on the upper
half of the body using acupuncture anesthesia. We found that the primary afferent fibers of the GAN from one animal project onto the ipsilaterai reticular parvicellular nucleus of the medulla oblongata. Shriver et al. had found that in two cases the degenerated fibers were seen at the same place following C2 dorsal root section 5. The connectivity in the reticular formation of the medulla oblongata is very complicated where various sensations are converged. Electrophysiological study shows that the reticular formation of the medulla oblongata has played some roles in inhibiting visceralgesia. Labeled cells were seen in ipsilateral superior cervical ganglia, which indicated that the GAN contains sympathetic fibers. This study demonstrates that the primary afferent fibers of the GAN and other peripheral nerves may well converge on the upper cervical cord, the nucleus of the spinal tract of the trigeminal nerve and the solitary nucleus of the medulla oblongata, which may be regarded as an anatomical basis for explah~ing the clinical phenomena that trigeminal neuralgia may be healed when the GAN is sectioned, the pain in the area of the upper neck may be referred to regions of the head and headache may be also referred to regions of the upper neck, etc.
REFERENCES
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ACKNOWLEDGEMENTS The authors wish to thank Prof. Xu Qian for his help in preparing this article.