Brainstem cells of origin of physiologically identified cardiopulmonary nerves in the rhesus monkey (Macaca mulatta)

The distributions of brainstem cells of origin of the cervical vagus nerve, its cervical and thoracic branches, and of neurons projecting to the cricothyroid muscle and the stomach wall were identified and compared following injections of horseradish peroxidase (HRP) in 18 Rhesus monkeys. Physiologically and/or anatomically identified cardiopulmonary nerves were injected with 3–20 μl of HRP to identify the locations of vagal preganglionic cardioinhibitory neurons in 10 of these monkeys. After injections into cardiopulmonary nerves, retrogradely labelled cells were concentrated ipsilaterally in the most lateral parts of the dorsal motor nucleus of the vagus nerve (DMV) and in the ventrolateral nucleus ambiguus (NA). Fewer labelled neurons were identified close to or in the principal (dorsal) division of the NA and in the intermediate zone between the DMV and NA. The results indicate that monkey cardiopulmonary nerves have multiple origins; their somata are located primarily in the ventrolateral NA and to a lesser extent in the lateral DMV. In monkeys, there is a stronger representation in the lateral DMV than in cat, dog and pig. The viscerotopic organization of the cells of origin of primate vagal nerves is similar to that in other species. The cells of origin of vagal projections to the superior laryngeal nerve and cricothyroid muscle were located in the NA rostrally to those of the inferior laryngeal nerve. Injections into the superior laryngeal nerve also resulted in significant labelling in the DMV and intermediate zone (IZ). The cells of origin of projections to the anterior stomach wall were restricted to the DMV with a bilateral distribution of labelled cells, concentrated medially in the nucleus.     

Fibers supplying the laryngeal musculature in the cranial root of the rabbit accessory nerve: Nucleus of origin, peripheral course, and innervated muscles

The location of the rabbit laryngeal motoneurons whose axons traverse the cranial root of the accessory nerve was studied with injection of HRP or nuclear yellow into the laryngeal muscles in combination with the intracranial severing of either the rootlets of the vagus nerve or those of the cranial root. The motoneurons were located in the diffuse cell group that forms a subnucleus occupying the caudal two-thirds of the nucleus ambiguus and sending fibers to the inferior laryngeal nerve. The caudal one-third of the diffuse cell group supplying the lateral cricoarytenoid muscle, was occupied only by these motoneurons, whereas in its rostral two-thirds, they were intermingled with motoneurons having axons that traversed the vagal rootlets. The thyroarytenoid and posterior cricoarytenoid motoneurons are present in the rostral two-thirds of the diffuse cell group; axons of the former traversed the rootlets of the cranial root, and of the latter traversed the vagal rootlets. On the other hand, the medial scattered cell group, located in the rostral one-third of the nucleus ambiguus and sending fibers to the cricothyroid muscle via the superior laryngeal nerve, contained only motoneurons with axons traversing the vagal rootlets. The above findings clarified that fibers of the cranial root enter the inferior laryngeal nerve after joining the vagus, and then reach the adductor muscles for the vocal fold, with their neurons of origin in a caudal portion of the nucleus ambiguus. The vagal rootlet fibers, with their neurons of origin situated more rostrally in the nucleus, innervate the tensor and abductor muscles via the superior and inferior laryngeal nerve, respectively.     

The central distribution of the cervical vagus nerve and gastric afferent and efferent projections in the rat

The medullary distribution of afferent fibers and cells of origin of the cervical vagal trunk and of the vagal innervation of the stomach have been studied using the anterograde and retrograde transport of horseradish peroxidase (HRP). Injections of HRP were made into the cervical vagus nerve, the stomach wall, the proximal small intestine, or the peritoneal cavity. Two to four days following the injections, the rats were perfused and the medullae oblongatae and nodose ganglia were processed using the tetramethyl benzidine method. Cervical vagus nerve injections of HRP resulted in heavy anterograde labeling in the ipsilateral nucleus of the tractus solitarius (NTS) and the commissural nucleus. Lighter labeling was seen in these regions on the contralateral side, but did not extend as far rostrally in the NTS. Labeling was also seen in the area postrema. Retrogade labeling of somata was present in the ipsilateral side in the nodose ganglion, throughout the whole extent of the dorsal motor nucleus of the vagus, much of the nucleus ambiguus and in rostral levels of the cervical spinal cord. After stomach injections, labeling indicative of afferent fibers was observed bilaterally in the dorsomedial and medial portions of the NTS and in the commissural nucleus. Labeled efferent fibres arose from neurons in the dorsal motor nucleus of the vagus, nucleus ambiguus and the cervical spinal cord. Retrogradely labeled somata were found bilaterally, throughout the rostrocaudal length of the dorsal motor nucleus in all cases with stomach injections. In some, but not all cases, labeled somata were seen bilaterally in compact areas within the nucleus ambiguus, particularly rostrally. Control injections of HRP into the intestinal wall and peritoneal cavity indicated that the stomach was the primary source of afferent and efferent labeling in the medulla following subdiaphragmatic injections.     

Brainstem cells of origin of the cervical vagus and cardiopulmonary nerves in the neonatal pig (Sus scrofa)

The distribution of the cells of origin of the cervical vagus and cardiopulmonary nerves has been studied in neonatal piglets (Sus scrofa) ranging in age from 1 to 60 days. Cardiopulmonary nerves were identified physiologically and anatomically prior to injection of horseradish peroxidase (HRP) into the nerves. Following injection of HRP into the cervical vagus nerve retrogradely labeled neurons were present in the dorsal motor nucleus of the vagus nerve (DMV), the nucleus of the solitary tract, the nucleus ambiguus (NA), ventrolateral to the NA and in an intermediate zone between the DMV and the NA. Two unique clusters of neurons were also retrogradely labeled after injections into the vagus nerve. One group was located lateral to the most caudal levels of the DMV and extended as far caudally as the C1 spinal segment. The second distinctive group was located ventrolateral to the nucleus ambiguus in a cell column identified as the ventrolateral nucleus ambiguus (VLNA). After injections of HRP into cardiopulmonary nerves, the majority of neurons were found in the VLNA and the distinct clusters of neurons in this cell column were particularly heavily labeled. Small numbers of cells were labeled in the DMV and NA and none were labeled in the solitary nucleus after cardiopulmonary nerve injections. There were no apparent age-related differences in the degree or distribution of retrograde labeling.The distribution of neurons in the medulla oblongata projecting into cardiopulmonary nerves in the piglet is similar to that described in other species, i.e., the nucleus ambiguus, particularly its ventrolateral cell column, is the primary site of cardiomotor neurons. In addition, in the piglet there is a morphologically distinct cluster of cells related to the heart, and possibly the lungs, which does not appear to be present in other species.     

Medullary cells of origin of vagal cardioinhibitory fibers in the pigeon. I. Anatomical studies of peripheral vagus nerve and the dorsal motor nucleus

The organization to the dorsal motor nucleus of the vagus in the pigeon was studied in an attempt to localize the cells of origin of vagal cardioinhibitory fibers. The course of the peripheral vagus nerve is described form the intracranial rootlets to abdominal levels. Using combined microdissection and electrical stimulation techniques, the branches which mediate cardiodeceleration are found to arise from a localized segment of the vagal trunk below the thoracic ganglion, and above the level where the left and right vagi join. The dorsal motor nucleus, its cytoarchitectonic divisions, and other structures connected with vagal rootlets are described on the basis of normal material. Utilizing the above findings a series of retrograde degeneration experiments was undertaken. The distribution of chromatolytic neurons following cervical vagotomy was described to indicate the extent of the dorsal motor nucleus. Selective nerve sections (abdominal vagotomy, cardiac vagotomy, recurrent laryngeal neurotomy, or pneumonectomy) then indicated that there is an incompletely inverted topographic representation of the vagus nerve in the dorsal motor nucleus, including a representation of the recurrent laryngeal nerve; no evidence was found for the existence of a nucleus ambiguus. The vagal cardioinhibitory fibers appear to be represented throughout the rostral half of the nucleus, but they are most concentrated in the ventral portion of the nucleus, approximately three-quarters of a millimeter rostral to the obex.     

Observations on the afferent and efferent organization of the vagus nerve and the innervation of the stomach in the squirrel monkey

Horseradish peroxidase was injected into the cervical vagus nerve or stomach wall of adult squirrel monkeys. Following cervical vagus nerve injections, labelled afferent fibres were present in the tractus solitarius and labelled fibres and terminals were present in medial and lateral parts of the nucleus of the tractus solitarius (NTS) ipsilaterally. Afferent labelling was also seen in the ipsilateral commissural nucleus and in the area postrema. Labelling was present contralaterally in caudal levels of the medial parts of the NTS, in the commissural nucleus, and in the area postrema. Afferent projections to the ipsilateral pars interpolaris of the spinal trigeminal nucleus and to the substantia gelatinosa of the C1 segment of the spinal cord were also labelled. Following injections of HRP into the anterior and posterior stomach walls, the tractus solitarius was labelled bilaterally. Afferent labelling was concentrated bilaterally in the dorsal parts of the medial division of the NTS, i.e., in the subnucleus gelatinosus, and in the commissural nucleus. The regions of NTS immediately adjacent to the tractus solitarius were largely unlabelled. Injections of HRP into the cervical vagus nerve resulted in heavy retrograde labelling of neurons in the ipsilateral dorsal nucleus of the vagus (DMX) and in the nucleus ambiguus (NA). In addition a few neurones were labelled in the intermediate zone between these two nuclei. Retrogradely labelled neurons were also present in the nucleus dorsomedialis in the rostral cervical spinal cord and in the spinal nucleus of the accessory nerve. Injections of HRP into the left cricothyroid muscle in two cases resulted in heavy retrograde labelling of large neurons in the left NA. Following stomach wall injections of HRP retrograde labelling of neurons was seen throughout the rostrocaudal and mediolateral extent of the DMX; there was no apparent topographical organization of the projection. In these cases, a group of labelled smaller neurons was found lying ventrolateral to the main part of the NA through its rostral levels. This study in a primate indicates that a large vagal afferent projection originates in the stomach wall and terminates primarily in the subnucleus gelatinosus of the NTS and in the commissural nucleus with a distribution similar to that described previously in studies in several subprimate mammalian species. The present results and those of other studies suggest some degree of segregation of visceral input within different subnuclei of the NTS.(ABSTRACT TRUNCATED AT 400 WORDS)     

Electrophysiological and functional identification of different neuronal types within the nucleus ambiguus in the cat

Extracellular single neuron recording in nucleus ambiguus demonstrates the existence of different neuronal classes within its electrophysiological limits. Laryngeal motoneurons were identified by their antidromic activation from the recurrent laryngeal and vagus nerves. Interneurons were identified by their antidromic activation from the contralateral cervical spinal cord. Stimulation of the ipsilateral superior laryngeal nerve activated synaptically all laryngeal motoneurons recorded but not interneurons. Most motoneurons and all interneurons showed spontaneous discharges during the inspiratory phase of the respiratory cycle. A few expiratory motoneurons were also recorded. In addition to laryngeal motoneurons and interneurons vagal stimulation also activated a population of efferent neurons located in the nucleus ambiguus with firing patterns not related to respiration. Functional implications of described findings are discussed.     

Organization within the cranial IX-X complex in ranid frogs: a horseradish peroxidase transport study

Cranial nerves IX and X in frogs have been described as originating from a nuclear group referred to as the IX-X complex. We studied the central nervous system components of this complex in Rana pipiens and R. catesbiana by labeling peripheral branches of cranial nerves IX and X and identifying the central nervous system contributions of these branches. Various peripheral nerves (IX and the cardiac, gastric, pulmonary, and laryngeal branches of X) were identified and soaked in horseradish peroxidase (HRP). One to 2 weeks later, the frogs were killed and processed for HRP by the tetramethylbenzidine method. Glossopharyngeal efferents originated from a small ventrolateral cell group found at the level of IX root exit. Vagal efferents formed a single column of cells in a ventrolateral position from the level of the brainstem exist of the vagus nerve (approximately 2,000 micrometers above the obex) to 200 micrometers below the obex (values given are for an 80-g frog). This cell group was separate from and just caudal to efferent cells of the glossopharyngeal nerve. Within the vagal portion of the column, cells projecting through the gastric branch were found throughout the rostral-caudal extent of the nucleus. "Cardiac" cells tended to be more rostral than "pulmonary" cells, and both groups of cells were located in the middle of the nucleus. "Laryngeal" cells were located more caudally in the nucleus. This peripheral representation within the vagal nucleus corresponds more closely to the organization found in the mammalian nucleus ambiguus, rather than to the apparent lack of organization found in the mammalian dorsal motor nucleus. Afferents of IX and X entered slightly rostral to the ventral roots of their respective nerves and descended in two tracts. The majority entered the tractus solitarius and descended in a medial position to cervical spinal cord. A portion of the afferents from the vagus nerve crossed the midline in the lower myelencephalon just dorsal to the central canal and ascended a short distance on the contralateral side. Within the solitary tract, vagal afferents were located in a ventrolateral position as they descended to below the obex. Glossopharyngeal afferents filled the remainder of the tract. A smaller portion of afferents from both IX and X did not enter the solitary tract but descended in the spinal tract of V and the dorsolateral funiculus of the spinal cord (Lissauer's tract) to thoracic levels. Afferents of IX also formed a rostral bundle which extended in the solitary tract to the caudal metencephalon.     

Brainstem distribution of neurons with efferent projections in the cervical vagus of the dog

The distribution within the brainstem of cell bodies and efferent fibers projecting in the cervical vagus was studied with retrograde transport of horseradish peroxidase (HRP). Five to eight days after multiple microinjections of HRP into either the cervical vagosympathetic trunk or the nodose ganglion the brainstems and nodose ganglia were perfused and processed by the tetramethyl benzidine method. HRP-positive neurons were found in three brainstem regions: a dorsal cell column comprising the dorsal motor nucleus of the vagus (dmnX), a ventrolateral group in the region of nucleus ambiguus (nA), and scattered cells along a line between these columns. The density of labeled neurons was greatest within dmnX. Axons from cells of the ventrolateral column projected dorsomedially; just ventral to dmnX they turned laterally to exit the medulla in multiple rootlets. Within nA labelled neurons were distributed according to size, with larger cells more medial and smaller ones more lateral. Caudal to nA in nucleus retroambigualis and nucleus dorsalis medialis cell bodies appeared segregated into clusters.     

Cells of origin of motor axons in the subdiaphragmatic vagus of the rat

The central cell groups that give rise to the motor axons that travel in the subdiaphragmatic vagus were re-examined in the rat by transecting the dorsal or ventral vagus near the stomach and incubating the nerve stump in crystalline horseradish peroxidase (HRP). An exceedingly large percentage of cells was labeled throughout the dorsal motor nucleus of the vagus (mX), with labeled cells extending even beyond the rostro-caudal limits of the nucleus usually assigned on the basis of cytoarchitecture alone. Different patterns of cell-labeling could be correlated with one or the other of the two vagal branches. Incubation of the ventral branch labeled cells only in the left mX, while incubation of the dorsal branch labeled cells on both sides, although more extensively on the right. HRP-positive somata were also observed bilaterally in the nucleus ambiguus (NA) after incubation of either branch of the subdiaphragmatic vagus; this finding is in contrast to previous accounts in which motor fibers from NA were considered to project only to cervical and thoracic structures. These results suggest that mX and NA are responsible for a substantial component of abdominal innervation in the rat.     

Distribution of motoneurons in the brain stem of monkeys, innervating the larynx

Following HRP (Horseradish Peroxidase) injections to cricothyroid muscle, recurrent laryngeal nerve and the vagal nerve at the level of nodose ganglion, labeled motoneurons were found to show a characteristic distribution in the brain stem of the monkey. Cricothyroid motoneurons extended from a level caudal to the facial nucleus to a level caudal to the middle part of the inferior olivary nucleus (IO) and were scattered around the outer area of nucleus ambiguus (Amb). Motoneurons supplying the recurrent laryngeal nerve were found between a level rostral to the middle of IO and its caudal end. Distribution was compact in the lateral part, but was scattered in the dorsomedial part of Amb. On injection of HRP into the nodose ganglion of the vagal nerve, labeled motoneurons were seen in two cell columns: In the Amb and in the dorsal motor nucleus of the vagus. The former extended from the rostral level of IO to the caudal end of IO, also showing connections with the retroambigual nucleus.     

Localization of cardiac vagal preganglionic motoneurones in the rat: Immunocytochemical evidence of synaptic inputs containing 5-hydroxytryptamine

The origin of cardiac vagal preganglionic motoneurones in the rat is still controversial and knowledge of the chemistry of synaptic inputs onto these neurones is limited. In this investigation vagal preganglionic motoneurones innervating the heart were identified by the retrograde transport of cholera toxin conjugated to horseradish peroxidase (CT-HRP) combined with the immunocytochemical localization of 5-hydroxytryptamine. Injection of CT-HRP into the myocardium resulted in the retrograde labelling of neurones primarily in the ventral regions of the nucleus ambiguus (75.1%). Labelled neurones were also distributed in a narrow band through the reticular formation extending between the dorsal motor nucleus of the vagus nerve and the nucleus ambiguus (17.3%) as well as in the dorsal motor nucleus itself (7.6%). A combination of retrograde labelling with immunocytochemistry for 5-hydroxytrypta-mine revealed that the neuronal perikarya and the dendrites of cardiac vagal motoneurones in the nucleus ambiguus were often ensheathed in 5-hydroxytryptamine-immunoreactive axonal boutons. Electron microscopic examination of this material confirmed that there were synaptic specializations between these boutons and the cardiac vagal motoneurones. The identification of 5-hydroxytryptamine-containing synaptic inputs to this population of vagal motoneurones provides further detail towards the understanding of the regulation of heart rate by the parasympathetic nervous system. © 1993 Wiley-Liss, Inc.     

Reflex connections of the facial and vagal gustatory systems in the brainstem of the bullhead catfish, Ictalurus nebulosus

The primary gustatory sensory nuclei in catfish are grossly divisible into a vagal lobe and a facial lobe. In this study, the reflex connections of each gustatory lobe were determined with horseradish peroxidase (HRP) tracing methods. In addition, in order to determine the loci and morphology of the other brainstem cranial nerve nuclei, HRP was applied to the trigeminal, facial, glossopharyngeal, or vagus nerve. The sensory fibers of the facial nerve terminate in the facial lobe. The facial lobe projects bilaterally to the posterior thalamic nucleus, superior secondary gustatory nucleus, and medial reticular formation of the rostral medulla. The facial lobe has reciprocal connections with the n. lobobulbaris, medial reticular formation of the rostral medulla, descending trigeminal nucleus, medial and lateral funicular nuclei, and the vagal lobe, ipsilaterally; and with the facial lobe contralaterally. In addition, the facial lobe receives inputs from the raphe nuclei, from a pretectal nucleus, and from perilemniscal neurons located immediately adjacent to the ascending gustatory lemniscal tract at the level of the trigeminal motor nucleus. The gustatory fibers of the vagus nerve terminate in the vagal lobe, while the general visceral sensory fibers terminate in a distinct general visceral nucleus. The vagal lobe projects ipsilaterally to the superior secondary gustatory nucleus, lateral reticular formation, and n. ambiguus; and bilaterally to the commissural nucleus of Cajal. The vagal lobe has reciprocal connections with the ipsilateral lobobulbar nucleus and facial lobe. In addition, the vagal lobe receives input from neurons of the medullary reticular formation and perilemniscal neurons of the pontine tegmentum. In summary, the facial gustatory system has connections consonant with its role as an exteroceptive system which works in correlation with trigeminal and spinal afferent systems. In contrast, the vagal gustatory system has connections (e.g., with the n. ambiguus) more appropriate to a system involved in control of swallowing. These differences in central connectivity mirror the reports on behavioral dissociation of the facial and vagal gustatory systems.     

Collaterals of recurrent laryngeal nerve fibres innervate the thymus: a fluorescent tracer and HRP investigation of efferent vagal neurons in the rat brainstem

The origin and course of efferent vagal fibers, which innervate the rat thymus, were investigated by a fluorescent retrograde double labeling method, using Fast blue (FB) and Diamidino yellow dihydrochloride (DY) as tracers. In the same animal, one tracer was injected into the cranial portion of the right lobe of the thymus and the other dye was deposited around the cut end of the right recurrent laryngeal nerve. The neuronal population giving origin to the recurrent nerve was mapped by using retrograde labeling with HRP applied to the central stump of the nerve. The HRP retrograde axonal transport showed that most efferent vagal fibers of the recurrent nerve have their perikarya in the nucleus retroambigualis (NRA), nucleus ambiguus (NA), and to a lesser extent in the nucleus retrofacialis (NRF). In fluorescent retrograde double labeling of thymus and recurrent laryngeal nerve both single and double labeled cells were found. The cells labeled by the injections into the thymus were colocalized with the neurons labeled by the tracer deposited in the recurrent laryngeal nerve to the NRA, NA, and NRF. Moreover along the rostrocaudal extent of the NRF and NA double labeled cells were present, showing that some of the thymic efferents are collaterals of the recurrent nerve fibers. Our experiments shown that some thymic vagal fibres originate from neurons of nucleus dorsalis nervi vagi (NDV) as demonstrated both by HRP and FB injected thymuses. The possible role of these efferents in thymic function is briefly discussed.     

Projections from the nucleus tractus solitarii to the rostral ventrolateral medulla

Projections from the nucleus tractus solitarii (NTS) to autonomic control regions of the ventrolateral medulla, particularly the nucleus reticularis rostroventrolateralis (RVL), which serves as a tonic vasomotor center, were analyzed in rat by anterograde, retrograde, and combined axonal transport techniques. Autonomic portions of the NTS, including its commissural, dorsal, intermediate, interstitial, ventral, and ventrolateral subnuclei directly project to RVL as well as to other regions of the ventrolateral medulla. The projections are organized topographically. Rostrally, a small cluster of neurons in the intermediate third of NTS, the subnucleus centralis, and neurons in proximity to the solitary tract selectively innervate neurons in the retrofacial nucleus and nucleus ambiguus. Neurons generally located in more caudal and lateral sites in the NTS innervate the caudal ventrolateral medulla (CVL). The RVL, CVL, and nucleus retroambiguus are interconnected. A combined retrograde and anterograde transport technique was developed so as to prove that projections from the NTS to the ventrolateral medulla specifically innervate the region of RVL containing neurons projecting to the thoracic spinal cord or the region of the nucleus containing vagal preganglionic neurons. When the retrograde tracer, fast blue, was injected into the thoracic spinal cord, and wheat germ agglutinin-conjugate horseradish peroxidase (HRP) was injected into the NTS, anterogradely labeled terminals from the NTS surrounded the retrogradely labeled neurons in the RVL and in the nucleus retroambiguus in the caudal medulla. Among the bulbospinal neurons in the RVL innervated by the NTS were adrenaline-synthesizing neurons of the C1 group. When fast blue was applied to the cervical vagus, and HRP was injected into the NTS, anterogradely labeled terminals from the NTS surrounded retrogradely labeled neurons in the rostral dorsal motor nucleus of the vagus, the region of the nucleus ambiguus, the retrofacial nucleus, and the dorsal portion of the RVL, a region previously shown to contain cardiac vagal preganglionic neurons. This combined anterograde and retrograde transport technique provides a useful method for tracing disynaptic connections in the brain. These data suggest that the RVL is part of a complex of visceral output regions in the ventrolateral medulla, all of which receive afferent projections from autonomic portions of the NTS. Bulbospinal neurons in the RVL, in particular the C1 adrenaline neurons, may provide a portion of the anatomic substrate of the baroreceptor and other visceral reflexes.     

The origin of brainstem-spinal pathways in the north american opossum (didelphis virginiana). Studies using the horseradish peroxidase method

Brainstem neurons which project to lumbar, thoracic and cervical spinal levels have been identified in the North American opossum by the horseradish peroxidase (HRP) technique. Neurons which relay to all of the levels studied are located within the medullary and pontine reticular formation as well as within the nucleus cuneatus, the nucleus of the tractus solitarius, the lateral reticular nucleus, the medullary and caudal pontine raphe nuclei, the lateral, medial and inferior vestibular nuclei, the nucleus “F,” the nucleus coeruleus, and the nucleus coeruleus, para α, the red nucleus, and the interstitial nucleus of Cajal. The lateral vestibulospinal and rubrospinal systems are topographically organized, although neurons projecting to different cord levels show considerable intermingling. Our material also provides evidence that raphe-spinal and reticulospinal connections are organized to some degree. Neurons which backfill after cervical and thoracic placements, but not after lumbar injections, are distributed within the caudal spinal trigeminal nucleus, the nucleus intercalatus, the dorsal vagal nucleus, the cuneiform area of Castaldi, the fields of Forel, and the nucleus of Darkschewitsch. Reactive neurons are present within the lateral, dorsal and posterior hypothalamic areas as well as within the periventricular and paraventricular nuclei after thoracic placements and within the superior colliculus after injections within the cervical cord. Additionally, neurons are reactive in the nucleus ambiguus, the interpolar division of the spinal trigeminal nucleus and the rostral division of the oculomotor nucleus (Oswaldo-Cruz and Rocha-Miranda, '68) after HRP placements into the third and fourth cervical segments.     

Localization and acetylcholinesterase content of vagal efferent neurons

The acetylcholinesterase (AChE) content of rat vagal efferent neurons was studied. Retrograde transport of horseradish peroxidase (HRP) by cut vagal axons provided a means for localizing efferent cell bodies; tissue sections were then processed for the simultaneous visualization of HRP and AChE. A dorsal vagal efferent column contained the dorsal motor nucleus of the vagus, as a primary component, and extended caudally into the upper cervical spinal cord. A ventral column contained neurons in the nucleus ambiguus and the surrounding reticular formation. Although most of the vagal efferent neurons stained with moderate to heave intensity for AChE there were some HRP-labeled cells that contained little AChE and a small percentage in which AChE was absent. In spite of the fact that AChE has been demonstrated in certain non-cholinergic neurons, it has also been found in all cholinergic neurons. Therefore, the presence of AChE has been regarded as a necessary (but not sufficient) component for identifying cholinergic neurons. The absence of AChE in a small percentage of the vagal efferent neurons indicates that some preganglionic parasympathetic fibers in the vagus nerve are not cholinergic.     

Localization of brain stem motoneurons innervating the laryngeal muscles in the rufous horseshoe bat,rhinolophus rouxi

The motoneurons innervating the laryngeal muscles were localized in the rufous horseshoe bat,Rhinolophus rouxi, using the HRP method. HRP was applied to the cricothyroid muscle and to the cut end of the recurrent laryngeal nerve. Labeled motoneurons were found in two completely separated regions of the nucleus ambiguus. The motoneurons innervating the cricothyroid muscle via the superior laryngeal nerve (SLN) are located withinn the ventrolateral portion of the nucleus reaching the caudal pole of the motor nucleus of the facial nerve. The motoneurons innervating the other intrinsic laryngeal muscles via the recurrent laryngeal nerve (RLN) are situated in the caudal half of the nucleus ambiguus. The innervation is strictly homolateral.     

The motor nuclei and primary projections of the IXth,Xth, XIth,and XIIth cranial nerves in the monitor lizard,Varanus exanthematicus

The motor nuclei and sensory connections of the IXth, Xth, XIth, and XIIth cranial nerves of the reptile Varanus exanthematicus were studied with the methods of anterograde degeneration and anterograde and retrograde axonal transport. The motor nuclei of nerve IX are located ventrally in the rhombencephalon and are constituted medially by the large-celled glossopharyngeal part of the nucleus ambiguus and laterally by the small-celled nucleus salivatorius inferior. The motor nuclei of nerve X consist of the dorsomedially located dorsal motor nucleus of the vagus and the laterally located vagal part of the nucleus ambiguus. The rostral portion of the latter cell group contains smaller cells than its caudal portion and is rostrally continuous with the nucleus salivatorius inferior of nerve IX. The efferent axons of nerves IX and X arising from the ventrolateral medulla first course dorsomedially, form genua beneath the IVth ventricle, and then exit the brainstem. All primary afferent fibers of nerve IX and the majority of those of nerve X enter the solitary tract. Terminations of vagal fibers were observed in the postvagal portion of the nucleus of the solitary tract, the dorsal motor nucleus of the vagus, and the nucleus of the commissura infima. A small contingent of vagal fibers courses caudally just dorsolateral to the descending trigeminal tract. A separate spinal component of nerve XI could not be found. The bulbar component of this nerve forms part of nerve X and takes its main origin from a detached caudal element of the nucleus ambiguus. The motor nuclear complex of nerve XII consists of a large dorsal nucleus and a small ventral nucleus that extend from the medulla oblongata into the first segment of the cervical spinal cord.     

Morphological and electrophysiological evidence for postsynaptic localization of functional oxytocin receptors in the rat dorsal motor nucleus of the vagus nerve

The vagal complex is innervated by oxytocin immunoreactive axons of hypothalamic origin. The presence of oxytocin binding sites in the dorsal motor nucleus of the vagus nerve of the rat was evidenced by autoradiography with a radioiodinated oxytocin antagonist as ligand. Two weeks following a unilateral vagotomy, distal to the nodose ganglion, binding sites were reduced below the level of detection in the ipsilateral dorsal motor nucleus of the vagus nerve. Choline acetyltransferase immunoreactivity was also markedly reduced in the vagal motoneurons whose axons had been transected. Electrophysiological studies were performed in vitro in brainstem slices from control rats. In antidromically identified vagal motoneurones, oxytocin applied at 0.1-1.0 microM either caused a reversible depolarization or generated, under voltage-clamp conditions, a transient inward current. These responses persisted under the condition of synaptic uncoupling. Taken together these observations favour the notion that oxytocin of hypothalamic origin acts directly on rat vagal motoneurones.