Evidence for the existence of L-dopa- and dopamine-immunoreactive nerve cell bodies in the caudal part of the dorsal motor nucleus of the vagus nerve

The precise neurochemical nature of tyrosine hydroxylase-immunoreactive neurons lying in the caudal part of the dorsal motor nucleus of the vagus nerve of the rat has been identified by immunohistochemistry of the catecholamines themselves. This region corresponds precisely to the area where tyrosine hydroxylase has been previously shown to be colocalized with choline acetyltransferase. Adjacent serial cryostat sections from the medulla oblongata and from the cervical spinal cord were treated either for choline acetyltransferase immunohistochemistry, aromatic L-amino acid decarboxylase and tyrosine hydroxylase immunolabelling or for tyrosine hydroxylase, dopamine, noradrenaline and L-dihydroxyphenylalanine (DOPA) immunostaining. The procedure involved the peroxidase-antiperoxidase method and an intensified diaminobenzidine reaction with imidazole. While no noradrenaline-positive cells were detectable in the dorsal motor vagal nucleus, tyrosine hydroxylase-, dopamine- and DOPA-immunoreactive perikarya were seen in the medial half of this nucleus, caudally the obex level. These results led us to conclude that these tyrosine hydroxylase-positive cells were effectively of dopaminergic nature and therefore that dopamine is a neurotransmitter contained in some neurons of the dorsal motor vagal nucleus. In the light of previous data showing colocalization of tyrosine hydroxylase and choline acetyltransferase in neurons of this portion of the nucleus, colocalization of dopamine with acetylcholine appears most likely. This might shed some light on the physiological consequences of dopamine action at target parasympathetic organs, such as the gastrointestinal tract.     

Morphological characteristics of the cranial root of the accessory nerve

There has been the controversy surrounding the cranial root (CR) of the accessory nerve. This study was performed to clarify the morphological characteristics of the CR in the cranial cavity. Fifty sides of 25 adult cadaver heads were used. The accessory nerve was easily distinguished from the vagus nerve by the dura mater in the jugular foramen in 80% of 50 specimens. The trunk of the accessory nerve from the spinal cord penetrated the dura mater at various distances before entering the jugular foramen. In 20% of the specimens there was no dural boundary. In these cases, the uppermost cranial rootlet of the accessory nerve could be identified by removing the dura mater around the jugular foramen where it joined to the trunk of the accessory nerve at the superior vagal ganglion. The cranial rootlet was formed by union of two to four short filaments emerging from the medulla oblongata (66%) and emerged single, without filament (34%), and usually joined the trunk of the accessory nerve directly before the jugular foramen. The mean number of rootlets of the CR was 4.9 (range 2–9) above the cervicomedullary junction. The CR of the accessory nerve was composed of two to nine rootlets, which were formed by the union of two to four short filaments and joined the spinal root of the accessory nerve. The CR is morphologically distinct from the vagus nerve, confirming its existence. Clin. Anat. 27:1167–1173, 2014. © 2014 Wiley Periodicals, Inc.     

Is the cranial accessory nerve really a portion of the accessory nerve? Anatomy of the cranial nerves in the jugular foramen

The accessory nerve is traditionally described as having both spinal and cranial roots, with the spinal root originating from the upper cervical segments of the spinal cord and the cranial root originating from the dorsolateral surface of the medulla oblongata. The spinal rootlets and cranial rootlets converge either before entering the jugular foramen or within it. In a recent report, this conventional view has been challenged by finding no cranial contribution to the accessory nerve. The present study was undertaken to re-examine the accessory and vagus nerves within the cranium and jugular foramen, with particular emphasis on the components of the accessory nerve. These nerves were traced from their rootlets attaching to the spinal cord and the medulla and then through the jugular foramen. The jugular foramen was exposed by removing the dural covering and surrounding bone. A surgical dissecting microscope was used to trace the roots of the glossopharyngeal nerve (CN IX), vagus nerve (CN X) and accessory nerve (CN XI) before they entered the jugular foramen and during their travel through it. The present study demonstrates that the accessory nerve exists in two forms within the cranial cavity. In the majority of cases (11 of 12), CN XI originated from the spinal cord with no distinct contribution from the medulla. However, in one of 12 cases, a small but distinct connection was seen between the vagus and the spinal accessory nerves within the jugular foramen.     

Vagal baro‐ and chemoreceptors in middle internal carotid artery and carotid body in rat

The glossopharyngeal nerve, via the carotid sinus nerve (CSN), presents baroreceptors from the internal carotid artery (ICA) and chemoreceptors from the carotid body. Although neurons in the nodose ganglion were labelled after injecting tracer into the carotid body, the vagal pathway to these baro‐ and chemoreceptors has not been identified. Neither has the glossopharyngeal intracranial afferent/sensory pathway that connects to the brainstem been defined. We investigated both of these issues in male Sprague–Dawley rats (n = 40) by injecting neural tracer wheat germ agglutinin‐horseradish peroxidase into: (i) the peripheral glossopharyngeal or vagal nerve trunk with or without the intracranial glossopharyngeal rootlet being rhizotomized; or (ii) the nucleus of the solitary tract right after dorsal and ventral intracranial glossopharyngeal rootlets were dissected. By examining whole‐mount tissues and brainstem sections, we verified that only the most rostral rootlet connects to the glossopharyngeal nerve and usually four caudal rootlets connect to the vagus nerve. Furthermore, vagal branches may: (i) join the CSN originating from the pharyngeal nerve base, caudal nodose ganglion, and rostral or caudal superior laryngeal nerve; or (ii) connect directly to nerve endings in the middle segment of the ICA or to chemoreceptors in the carotid body. The aortic depressor nerve always presents and bifurcates from either the rostral or the caudal part of the superior laryngeal nerve. The vagus nerve seemingly provides redundant carotid baro‐ and chemoreceptors to work with the glossopharyngeal nerve. These innervations confer more extensive roles on the vagus nerve in regulating body energy that is supplied by the cardiovascular, pulmonary and digestive systems.     

山羊迷走神经感觉纤维的来源——HRP法研究

为了探讨山羊迷走神经感觉纤维的来源,本文将HRP注入颈迷走神经干后,在结状节出现大量密集的标记细胞,颈静脉节中也有较多的细胞被标记,但其密度和数量远不如结状节。在颈1—8和胸1—3的背根节中出现一定数量的标记细胞。此外,少量的标记细胞见于迷走神经干的纤维束中,这些标记细胞的形态与结状节的基本相同。     

Projections from the nucleus of the solitary tract in the rat

The axonal projections of neurons in and near the nucleus of the solitary tract have been visualized using titrated amino acid autoradiography. Axons of neurons of this nucleus ramify extensively within the nucleus itself, but much less so in the nucleus commissuralis. They also enter cranial motor nuclei within the medulla. Axons originating in the anterior part of the nucleus of the solitary tract extend to the hypoglossal, facial and probably trigeminal motor nuclei, but not to the dorsal motor nucleus of the vagus or the nucleus ambiguus. The posterior part of the nucleus of the solitary tract projects to all these motor nuclei. In the spinal cord solitary nucleus axons remain in the medial gray directly caudal to the solitary nucleus itself. The distribution becomes very weak by C₃ after some fibers spread laterally into the caudal trigeminal nucleus. Fibers are labeled in the contralateral ventral columns, but they could not be unequivocably attributed to solitary neurons. Axons ascending from the nucleus of the solitary tract extend no further rostrally than the pons, where they terminate in the caudal end of the parabrachial nuclei.Although often treated as entirely separate systems, the present results indicate that secondary gustatory neurons in the anterior solitary nucleus and secondary visceral afferent neurons in the posterior solitary nucleus have very similar rostral and caudal projections. The pontine parabrachial nuclei, the rostral termination of solitary nucleus neurons, have extensive direct connections to the thalamus, the hypothalamus and the limbic forebrain. Assuming similar connections occur in other mammals, these findings establish the existence of di-synaptic visceral afferent access to the highest autonomic integrative centers in the brain.     

Electrophysiological mapping of sympathetic nuclei in the L2 and L3 segments of the spinal cord

The spinal sympathetic preganglionic nuclei were mapped using antidromic field potential analysis during electrical stimulation of L₂ and L₃ white rami. The spinal sympathetic nuclei were localized respectively in L₂ and L₃ segments of the lumbar cord as a narrow strip along craniocaudal axis of the spinal cord. The caudal and of each preganglionic sympathetic nucleus was localized caudally to the corresponding dorsal root entry (DRE). The cranial end of the nucleus in different experiments was localized at different levels along the corresponding DRE or cranial to the corresponding DRE. We suggest that neurones which send axons to a single white ramus form an anatomically separate sympathetic preganglionic nucleus in the lumbar spinal cord within one segment.     

鸡舌咽神经传入纤维在中枢的分布

目的 研究鸡舌咽神经传入纤维在中枢的分布。方法 选用10只健康来抗鸡,分离暴露舌咽神经干,在岩神经节处注射4μlCB－HRP,动物存活35小时,灌注固定,取延髓作冰冻连续切片,FMB法呈色,光镜下观察。结果 鸡舌咽神经传入纤维主要投射到注射侧孤束核闩前部的前中部,部分投身到三叉神经脊束与三叉神经脊束核、楔外侧核及第1、2颈髓脊侧角的背外侧。结论 鸡孤束核闩后部及闩前部的后部仅接受迷走传入投射,闩前部的前部同时接受迷走神经和舌咽神经的传入投射。     

Central projection of proprioceptive afferents arising from maxillo-facial regions in some animals studied by HRP-labeling technique

20 ICR mice (adult females) were used for analyzing the axonal projection of the trigeminal mesencephalic tract neurons and 10 Japanese shrew-moles for analyzing that of the snout proprioceptive neurons. The HRP-labeled axons were found to be ipsilaterally terminated in the trigeminal motor nucleus, supratrigeminal nucleus and trigeminal main and spinal tract nuclei, lateral pontine-medullary reticular formation, vagal dorsal motor and hypoglossal nuclei and the lamina V of the C2 spinal cord segments. No HRP-labeled axons were found in the facial and solitary nuclei and the cerebellum. Also, the functional localization of the trigeminal mesencephalic tract neurons was analyzed with the retrograde tracers of fluorescent compounds injected into the jaw-closing muscles having spindles. The fluorescent-labeled neurons were found to be intermingled throughout the nucleus and clustered at the caudal level of the nucleus. Also, double or triple fluorescent-labeled neurons were not observed in the nucleus. The HRP-labeled axon bundle of the facial proprioceptive neurons are divided rostro-caudally into the shorter ascending and the longer descending roots, both running closely dorsal to the trigeminal spinal tract nucleus. The ascending root lies adjacently dorsal to the spinal tract nucleus, giving off the terminal fibers to it, to the wider area of the dorso-medial pontine nuclei and finally to the cerebellar nuclei. At the level of the facial inner genu, it turns medially to meet the facial nerve root, giving off the terminal fibers to the facial motor nucleus and to the raphe nuclei and to the opposite nuclei bilaterally. The HRP-labeled descending root takes the course caudally at least down to the C3 segment of the spinal cord, giving off the terminal fibers to the spinal tract nucleus, the nuclei of the IXth, Xth and XIIth cranial nerves and the pontine-medullary reticular formation. In the spinal cord, it descends bilaterally through the posterior fascicles, giving off the terminal fibers to the dorsal and ventral horns.     

Expression of c-JUN, JUN B and JUN D proteins in rat nervous system following transection of vagus nerve and cervical sympathetic trunk.

Expression of c-JUN, JUN B and JUN D proteins was investigated in axotomized neurons following transection of the vagus nerve and the cervical sympathetic trunk in the rat. Vagotomy induced the expression of c-JUN and JUN D in the nodose ganglion, dorsal motor nucleus of the vagus nerve and nucleus ambiguus, whereas JUN B was not expressed in these areas, c-JUN and JUN D appeared after 10 h in the nodose ganglion and after 24 h in the dorsal motor nucleus of the vagus nerve with a maximum of immunoreactivity after 48 h. The c-JUN protein remained expressed at an increased level up to 100 days, whereas the immunoreactivity of JUN D declined after five days. Crush of the vagus nerve initially evoked an intense expression of c-JUN and JUN D, but in the course of regeneration the expression of c-JUN and JUN D had returned to more basal levels after 100 days. Similar to vagotomy, application of colchicine and vinblastine on to the intact vagus nerve induced expression of c-JUN and JUN D. On the other hand, application of lidocaine prior to vagotomy did not prevent the expression of these proteins. Transection of the cervical sympathetic trunk induced expression of c-JUN and JUN D, but not of JUN B, in the preganglionic sympathetic neurons of thoracic spinal cord. In these neurons, expression of c-JUN was still enhanced after 60 days whereas JUN D had returned to basal level. One hour after vagotomy, c-JUN and JUN B were transynaptically expressed in the area of central termination of sensory vagal neurons and declined within 10 h to basal levels. JUN D showed a late onset of expression, it appeared after 5 h and persisted for 60 days in this area. We postulate that the expression of c-JUN and JUN D in axotomized neurons is induced by deprivation of a target-derived suppressor.     

The relationship of the medullary catecholamine containing neurones to the vagal motor nuclei

We have re-examined in the rat the nuclear localization of the medullary catecholamine-containing cell groups (A1 and A2) and their relation to the vagal motor nuclei using a double labeling method. The vagal nuclei were defined by the retrograde transport of horseradish peroxidase applied to the cervical vagus, and noradrenergic and adrenergic neurons were stained with the peroxidase-antiperoxidase immunocytochemical method using an antibody to dopamine beta-hydrolase. The method allows visualization of both labels within single neurons. The neurons of the A2 group are primarily distributed in both the nucleus of the solitary tract and the dorsal motor nucleus of the vagus in a complex interrelationship that depends on the rostrocaudal level. Caudal to the obex, cells of the dorsal motor nucleus of the vagus are scattered among cells immunoreactive for dopamine beta-hydroxylase in the area considered to be the commissural subnucleus of the nucleus of the solitary tract. At levels near and slightly rostral to the obex, the dopamine beta-hydroxylase-positive cells are largely confined to nucleus of the solitary tract. However, the rostral third of the A2 group lies predominantly within dorsal motor nucleus, as defined by horseradish peroxidase labeled cells, with only a few cells in the nucleus of the solitary tract. A subset of the dopamine beta-hydroxylase positive cells within the rostral dorsal motor nucleus of the vagus are also vagal efferents. Our results suggest that a second population of dopamine beta-hydroxylase positive vagal efferents may exist ventrolaterally where neurons of the AI cell group intermingle with those of nucleus ambiguus.     

Vagal nerve endings in visceral pleura and triangular ligaments of the rat lung

The inner thoracic cavity is lined by the parietal pleura, and the lung lobes are covered by the visceral pleura. The parietal and visceral plurae form the pleural cavity that has negative pressure within to enable normal respiration. The lung tissues are bilaterally innervated by vagal and spinal nerves, including sensory and motor components. This complicated innervation pattern has made it difficult to discern the vagal vs. spinal processes in the pulmonary visceral pleura. With and without vagotomy, we identified vagal nerve fibres and endings distributed extensively in the visceral pleura (‘P’‐type nerve endings) and triangular ligaments (‘L’‐type nerve endings) by injecting wheat germ agglutinin‐horseradish peroxidase as a tracer into the nucleus of solitary tract or nodose ganglion of male Sprague–Dawley rats. We found the hilar and non‐hilar vagal pulmonary pleural innervation pathways. In the hilar pathway, vagal sub‐branches enter the hilum and follow the pleural sheet to give off the terminal arborizations. In the non‐hilar pathway, vagal sub‐branches run caudally along the oesophagus and either directly enter the ventral‐middle‐mediastinal left lobe or follow the triangular ligaments to enter the left and inferior lobe. Both vagi innervate: (i) the superior, middle and accessory lobes on the ventral surfaces that face the heart; (ii) the dorsal‐rostral superior lobe; (iii) the dorsal‐caudal left lobe; and (iv) the left triangular ligament. Innervated only by the left vagus is: (i) the ventral‐rostral and dorsal‐rostral left lobe via the hilar pathway; (ii) the ventral‐middle‐mediastinal left lobe and the dorsal accessory lobe that face the left lobe via the non‐hilar pathway; and (iii) the ventral‐rostral inferior lobe that faces the heart. Innervated only by the right vagus, via the non‐hilar pathway, is: (i) the inferior (ventral and dorsal) and left (ventral only) lobe in the area near the triangular ligament; (ii) the dorsal‐middle‐mediastinal left lobe; and (iii) the right triangular ligament. Other regions innervated with unknown vagal pathways include: (i) the middle lobe that faces the superior and inferior lobe; (ii) the rostral‐mediastinal inferior lobe that faces the middle lobe; and (iii) the ventral accessory lobe that faces the diaphragm. Our study demonstrated that most areas that face the dorsal thoracic cavity have no vagal innervation, whereas the interlobar and heart‐facing areas are bilaterally or unilaterally innervated with a left‐rostral vs. right‐caudal lateralized innervation pattern. This innervation pattern may account for the fact that the respiratory regulation in rats has a lateralized right‐side dominant pattern.     

Transneuronal transport of herpes simplex virus from the cervical vagus to brain neurons with axonal inputs to central vagal sensory nuclei in the rat.

The recent introduction of live viruses as intra-axonal tracing agents has raised questions concerning which central neurons are transneuronally labelled after application of the virus to peripheral organs or peripheral nerves. Since the central connections of the vagus nerve have been well described using conventional neuronal tracing agents, we chose to inject Herpes Simplex Virus Type 1 into the cervical vagus of the rat. After survival times of up to 3 days the rat brains were processed immunohistochemically using a polyclonal antiserum against herpes simplex virus. Two days after injection of the virus we observed viral antigen in the area postrema and in the nucleus tractus solitarius and the dorsal motor nucleus of the vagus (dorsal vagal complex), principally ipsilaterally. At this survival time the viral antigen in the dorsal vagal complex was largely confined to glial cells. After 3 days the viral antigen was localized both in glia and in nerve cells within the dorsal vagal complex and in brain regions previously demonstrated, using conventional tracing procedures, to contain neurons with axonal projections to the dorsal vagal complex. This was true for medullary, pontine, midbrain and hypothalamic regions and for telencephalic regions including the amygdala, the bed nucleus of the stria terminalis, and the insular and medial frontal cortices. Many of the nerve cells containing viral antigen were displayed in a Golgi-like manner, with excellent visualization of the dendritic tree. Axonal processes, in contrast, were not visualized. We used co-localization studies to confirm previous findings concerning monoamine neurotransmitter-related antigens present in medullary and pontine neurons projecting to the dorsal vagal complex. After 3 days there were many Herpes Simplex Virus Type 1-containing glial cells along the intra-medullary course of the vagal rootlets. However, no viral antigen was found in brain regions containing neurons whose axons pass through the region of glial cell-labelled rootlets. Glial cells containing viral antigen were particularly numerous in brain regions known to receive an input from neurons in the area postrema and the dorsal vagal complex. Taken together with our observation concerning the early appearance of viral antigen within glial cells in the dorsal vagal complex, this suggests that when the virus reaches the axon terminal portion it is transferred to nearby glial cells and possibly enters central neurons by way of these structures.     

The B?tzinger complex as the pattern generator for retching and vomiting in the dog.

To clarify the location of the pattern generator for the emetic act, the bulb was systematically stimulated and partially cut in decerebrate, paralyzed dogs. Stimulation of the following bulbar structures elicited the activities which could be recognized as retching and vomiting in the following muscle nerves. The bulbar structures were: the intra-bulbar bundle of the vagal afferents, the solitary tract and the medial subdivision of its nucleus (NTS), the area postrema, the commissural nucleus, the raphe area at the obex level, and the longitudinal reticular column which consists of 3 areas--the area between the caudal parts of the solitary complex (SC) and the nucleus ambiguus, the area ventromedial to the rostral part of the nucleus and the area dorsomedial to the retrofacial nucleus (RFN) which may correspond to the B?tzinger complex (BOT). The muscle nerves were: the phrenic branches to the dome and hiatal parts of the diaphragm, the abdominal muscle nerve, the pharyngo-esophageal branch of the vagus nerve, the mylohyoid muscle nerve, and the recurrent nerve branches to the adductors and abductor of the glottis. Emetic responses to stimulation of the vagal ventral trunk and the rostral SC still remained after cutting of the bilateral SCs at about 1 mm rostral to the obex, but disappeared after cutting at about 3.5 mm rostral to the obex. After the rostral cuts, stimulation of the SC part caudal to the cuts and the reticular column still induced the emetic act. Emetic responses to stimulation of the caudal SC remained after transection of the bulb at the rostral end of the RFN, but disappeared after transection at its caudal end or after partial cutting of the caudal BOT. The following hypothesis was proposed from these results. Emetic vagal afferents enter the rostral bulb, then descend through the SC to the area subpostrema. Subpostrema neurons project through the reticular column to the pattern generator of the emetic act in the BOT and activate it.     

An HRP study of location of the rabbit palatopharyngeal motoneurons and peripheral course of their axons

The location of the rabbit palatopharyngeal motoneurons and the peripheral course of their axons were investigated with intramuscular injection of HRP either in the normal animal or in conjunction with intracranial severing of the vagal rootlets. Labeled palatopharyngeal motoneurons were ipsilaterally located within a subdivision of the nucleus ambiguus which is formed by a compact arrangement of the smallest neurons of the nucleus and situated in the rostral of the nucleus. We named that subdivision the compact cell group (CoG). The labeled motoneurons occupied the caudal half of the CoG at a level from about 500 to 1,900 microns rostral to the obex. Labeling was completely abolished by severing the vagal rootlets, indicating that the axons of the palatopharyngeal motoneurons traversed the vagal rootlets.