Calcitonin gene-related peptide in nucleus ambiguus motoneurons in rat: viscerotopic organization

Genetic encoding of an esophageal motor circuit

Motor control of the striated esophagus originates in the nucleus ambiguus (nAmb), a vagal motor nucleus that also contains upper airway motor neurons and parasympathetic preganglionic neurons for the heart and lungs. We disambiguate nAmb neurons based on their genome-wide expression profiles, efferent circuitry, and ability to control esophageal muscles. Our single-cell RNA sequencing analysis predicts three molecularly distinct nAmb neuron subtypes and annotates them by subtype-specific marker genes: Crhr2, Vipr2, and Adcyap1. Mapping the axon projections of the nAmb neuron subtypes reveals that Crhr2^nAmb neurons innervate the esophagus, raising the possibility that they control esophageal muscle function. Accordingly, focal optogenetic stimulation of cholinergic Crhr2⁺ fibers in the esophagus results in contractions. Activating Crhr2^nAmb neurons has no effect on heart rate, a key parasympathetic function of the nAmb, whereas activating all of the nAmb neurons robustly suppresses heart rate. Together, these results reveal a genetically defined circuit for motor control of the esophagus.

Primary motor neurons for the esophagus reside in the nucleus ambiguus (nAmb) of the hindbrain, but little is known about their molecular identity. Coverdell et al. find that the nAmb comprises three molecularly and anatomically distinct neuron subtypes, one of which selectively innervates and can contract esophageal muscle.

Molecularly defined circuits for cardiovascular and cardiopulmonary control

The sympathetic and parasympathetic nervous systems powerfully regulate internal organs¹, but the molecular and functional diversity of their constituent neurons and circuits remains largely unknown. Here we use retrograde neuronal tracing, single-cell RNA sequencing, optogenetics, and physiological experiments to dissect the cardiac parasympathetic control circuit in mice. We show that cardiac-innervating neurons in the brainstem nucleus ambiguus (Amb) are comprised of two molecularly, anatomically, and functionally distinct subtypes. One we call ACV (ambiguus cardiovascular) neurons (~35 neurons per Amb), define the classical cardiac parasympathetic circuit. They selectively innervate a subset of cardiac parasympathetic ganglion neurons and mediate the baroreceptor reflex, slowing heart rate and atrioventricular node conduction in response to increased blood pressure. The other, ACP (ambiguus cardiopulmonary) neurons (~15 neurons per Amb) innervate cardiac ganglion neurons intermingled with and functionally indistinguishable from those innervated by ACV neurons, but surprisingly also innervate most or all lung parasympathetic ganglion neurons; clonal labeling shows individual ACP neurons innervate both organs. ACP neurons mediate the dive reflex, the simultaneous bradycardia and bronchoconstriction that follows water immersion. Thus, parasympathetic control of the heart is organized into two parallel circuits, one that selectively controls cardiac function (ACV circuit) and another that coordinates cardiac and pulmonary function (ACP circuit). This new understanding of cardiac control has implications for treating cardiac and pulmonary diseases and for elucidating the control and coordination circuits of other organs.

EA promotes swallowing via activating swallowing-related motor neurons in the nucleus ambiguus

To observe the effect of electroacupuncture (EA) on swallowing and its underlying mechanism, 32 Sprague-Dawley (SD) rats were chose and the electrophysiology was used to detect the discharge of nucleus ambiguus (NA) after EA at CV23 (Lianquan), GV16 (Fengfu), and other acupoints. The swallowing-related motor neuron was identified by antidromic stimulation through recurrent laryngeal nerve. Meanwhile, the swallowing numbers were induced by Double-distilled water (DDW) and the neuron discharges were recorded before and after EA. Beside, 50 SD rats were used for testing the c-fos expressions in NA after EA at different acupoints and the other 80 SD rats were used for chemical damage through the microinjection to bilateral NA. 58 neurons provided complete data after histological identification. And two types of swallowing-related (SR) motor neurons were identified, named spontaneous and silent neurons. We found that the onset latency of the first swallow was shorter and the swallowing numbers were increased after EA at CV23 than the other acupoints (P < 0.01). The excitatory neuron response rates were 66.67%, 71.11%, 42.22% and 35.56% for CV23, GV16, PC6 (Neiguan), and ST36 (Zusanli), respectively. The c-fos expressions on CV23 and GV16 groups were significantly higher than the other groups (P < 0.05). After chemical damage, the swallowing numbers could not be regulated by EA, but could be regulated by EA after fake damage. The results of the present study demonstrate that EA at CV23 and GV16 could regulate swallowing function via activating swallowing-related motor neurons in NA.

Expression of Sex Steroid Hormone Receptors in Vagal Motor Neurons Innervating the Trachea and Esophagus in Mouse

The medullary vagal motor nuclei, the nucleus ambiguus (NA) and dorsal motor nucleus of the vagus (DMV), innervate the respiratory and gastrointestinal tracts. We conducted immunohistochemical analysis of expression of the androgen receptor (AR) and estrogen receptor α (ERα), in relation to innervation of the trachea and esophagus via vagal motor nuclei in mice. AR and ERα were expressed in the rostral NA and in part of the DMV. Tracing experiments using cholera toxin B subunit demonstrated that neurons of vagal motor nuclei that innervate the trachea and esophagus express AR and ERα. There was no difference in expression of sex steroid hormone receptors between trachea- and esophagus-innervating neurons. These results suggest that sex steroid hormones may act on vagal motor nuclei via their receptors, thereby regulating functions of the trachea and esophagus.

Characterization of the vagal motor neurons projecting to the Guinea pig airways and esophagus

Distinct parasympathetic postganglionic neurons mediate contractions and relaxations of the guinea pig airways. We set out to characterize the vagal inputs that regulate contractile and relaxant airway parasympathetic postganglionic neurons. Single and dual retrograde neuronal tracing from the airways and esophagus revealed that distinct, but intermingled, subsets of neurons in the compact formation of the nucleus ambiguus (nAmb) innervate these two tissues. Tracheal and esophageal neurons identified in the nAmb were cholinergic. Esophageal projecting neurons also preferentially (greater than 70%) expressed the neuropeptide CGRP, but could not otherwise be distinguished immunohistochemically from tracheal projecting preganglionic neurons. Few tracheal or esophageal neurons were located in the dorsal motor nucleus of the vagus. Electrical stimulation of the vagi in vitro elicited stimulus dependent tracheal and esophageal contractions and tracheal relaxations. The voltage required to evoke tracheal smooth muscle relaxation was significantly higher than that required for evoking either tracheal contractions or esophageal longitudinal striated muscle contractions. Together our data support the hypothesis that distinct vagal preganglionic pathways regulate airway contractile and relaxant postganglionic neurons. The relaxant preganglionic neurons can also be differentiated from the vagal motor neurons that innervate the esophageal striated muscle.

Ambiguus motoneurons innervating laryngeal and esophageal muscles are malpositioned in the Reelin-deficient mutant rat, Shaking Rat Kawasaki

CONCLUSIONS

The present study confirmed that ambiguus motoneurons innervating intrinsic laryngeal and esophageal muscles are radially malpositioned in the brainstem of the Shaking Rat Kawasaki (SRK), a reelin-deficient mutant rat.

OBJECTIVES

Ambiguus motoneurons innervating the striated muscles of the larynx and esophagus take a long migration from their original birth plate in the floor of the fourth ventricle to their final settlement in the ventral margin of the medulla oblongata. To examine whether the migration of ambiguus nucleus neurons is affected in SRK, we studied localization of ambiguus motoneurons of postnatal day 21 (P21) normal and SRK rats.

MATERIALS AND METHODS

To label ambiguus motoneurons retrogradely, horseradish peroxidase (HRP) was injected into some laryngeal muscles including cricothyroid, thyroarytenoid and posterior cricoarytenoid muscles, and the cervical and abdominal esophageal muscles of the SRK and normal controls 2 days before sacrifice.

RESULTS

In the P21 normal rat, HRP-positive laryngeal and esophageal motoneurons were found in the nucleus ambiguus, whereas in the P21 SRK, they were scattered from the base of the fourth ventricle to the ventro-lateral margin of the medulla, suggesting that radial migration of ambiguus motoneurons from their birthplace to their final settlement is guided by Reelin protein.

Misidentification of cardiac vagal pre-ganglionic neurons after injections of retrograde tracer into the pericardial space in the rat

We evaluated whether pericardial injections of the retrograde tracers cholera toxin subunit B (CTb) or Fast Blue (FB) reliably labelled cardiac vagal pre-ganglionic neurons. Injections of CTb into the pericardial space of the rat labelled neurons in both the external and compact formations of the nucleus ambiguus. Most labelled neurons were found in the compact formation of the nucleus ambiguus, and the majority of these, and only these, expressed immunoreactivity for calcitonin gene-related peptide. This distribution of labelled neurons and their immunohistochemical properties is characteristic of oesophageal motoneurons. Examination of the oesophagus following intra-pericardial CTb applications revealed strong labelling of motor end plates within the skeletal muscle of the thoracic but not the abdominal oesophagus. When a second retrograde tracer, FB, was injected into the abdominal oesophagus, labelled somata were found adjacent to CTb-labelled neurons in the compact formation of the nucleus ambiguus. No co-localisation of tracers was found, but identical proportions of calcitonin gene-related peptide (CGRP) immunoreactivity were observed in both groups of neurons. FB injected into the pericardial space labelled intra-cardiac neurons but not brainstem neurons. We conclude that intra-pericardial, and perhaps sub-epicardial, injections of some retrograde tracers are likely to label a subset of oesophageal, as well as cardiac, vagal motor neurons in the brainstem.

Immunohistochemical characterization of cardiac vagal preganglionic neurons in the rat

Cardiac vagal preganglionic neurons (CVN) control cardiac activity by negative chronotropic, dromotropic and inotropic effects. We attempted to characterize the distribution and neuronal properties of the CVN by using double labeling with the retrograde tracer cholera toxin B subunit (CTb) and immunohistochemistry for choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), calcitonin gene-related peptide (CGRP) or nitric oxide synthase (NOS). Injection of CTb into the sinoatrial ganglia resulted in many retrogradely labeled of neurons in the dorsal motor nucleus of the vagus (DMV), the compact (AmC), semicompact (AmS), loose (AmL), external (AmE) formations of the nucleus ambiguus, and the intermediate zone (IZ) between DMV and the nucleus ambiguus. Almost all CTb-labeled neurons showed ChAT immunoreactivity in the DMV, AmC, AmS, AmL and IZ, but most of the CTb-labeled neurons showed no ChAT immunoreactivity in the AmE. Most of the CTb-labeled neurons were double-labeled with CGRP immunoreactivity in the AmC, AmS and AmL, but a few double-labeled neurons were found in the DMV, IZ and AmE. A few CTb-labeled neurons were double-labeled with NOS immunoreactivity only in the DMV. No TH-immunoreactive neurons were found among the CVN. These results indicate that there are four kinds of neurons among the CVN: non-cholinergic CVN in the AmE, cholinergic and CGRP-containing CVN in the AmC, AmS and AmL, and cholinergic or cholinergic and NOS-containing CVN in the DMV.

Monoaminergic and peptidergic axonal projections to the vagal motor cell column of a teleost, the filefish Stephanolepis cirrhifer

In an immunohistochemical study, the vagal motor nucleus of a teleost, the filefish Stephanolepis cirrhifer, could be divided into a rostral part and a caudal part, and the former into a dorsolateral group and a ventromedial group. The dorsolateral group consisted of neurons immunoreactive for calcitonin gene-related peptide, whereas the ventrolateral-caudal group was negative for calcitonin gene-related peptide. The latter group was retrogradely labeled after dextran amine injection to the visceral ramus of the vagus nerve, suggesting that it is a general visceral efferent column, made up of parasympathetic preganglionic neurons, whereas the dorsolateral rostral group is a special visceral efferent column. In the general visceral efferent column, a dense concentration of nerve fibers immunoreactive for serotonin, tyrosine hydroxylase, cholecystokinin-8, and substance P, and a small number of fibers immunoreactive for neuropeptide Y was observed. Perikarya in contact with varicose terminals immunoreactive for these substances were frequently seen. In contrast, in the special visceral efferent column, only a moderate concentration of neuropeptide Y-immunoreactive nerve fibers and a sparse distribution of fibers immunoreactive for tyrosine hydroxylase were observed. Perikarya in contact with varicose terminals immunoreactive for these substances were rare. These results suggest that the vagal parasympathetic preganglionic neurons might receive multiple inputs of monoaminergic and peptidergic fibers involved in the regulation of the visceral organs. On the other hand, monoaminergic and peptidergic afferent fibers might be of much less significance in the activity of the special visceral efferent component of the vagus nerve.

Laryngeal and respiratory protective reflexes

Swallowing is a complex motor behavior that relies on an interneuronal network of premotor neurons (PMNs) to organize the sequential activity of motor neurons that are active during the buccopharyngeal and esophageal phases. Swallowing PMNs are highly interconnected to multiple areas of the brain stem and the central nervous system and provide a potential anatomic substrate integration of swallowing activity with airway protective reflexes. Because these neurons have synaptic contact with both afferent inputs and motor neurons and exhibit a true central activity, they appear to constitute the swallowing central pattern generator. We studied the viscerotopic organization of the nucleus of the solitary tract (NTS), the nucleus ambiguus (NA), the dorsal motor nucleus (DMN), and the hypoglossal nucleus (XII) using cholera toxin horseradish peroxidase (CT-HRP), a sensitive antegrade and retrograde tracer that effectively labels afferent terminal fields within the NTS as well as swallowing motor neurons and their dendritic fields within the NA, DMN, and XII. We used CT-HRP to provide a comprehensive description of the dendritic architecture of NA motor neurons innervating swallowing muscles. We also conducted studies using pseudorabies virus (PRV), a swine alpha-herpesvirus, to map central neural circuits after injection in the peripheral or central nervous systems. One attenuated vaccine strain, Bartha PRV, has preferential affinity for sites of afferent synaptic contact on the cell body and dendrites and a reactive gliosis that effectively isolates the infected neurons and provides a barrier to the nonspecific spread to adjacent neurons. The findings provide a basis for the central integration of swallowing and respiratory protective reflexes.

Branchiogenic motoneurons innervating facial, masticatory, and esophageal muscles show aberrant distribution in the reeler-phenotype mutant rat, Shaking Rat Kawasaki

Shaking Rat Kawasaki (SRK) is an autosomal recessive mutant rat that is characterized by cerebellar ataxia. Although previous studies indicated many points of similarity between this mutant rat and the reeler mouse, nonlaminated structures such as the facial nucleus have not been studied in this mutant rat. Nissl-stained sections through the brainstem showed that the cytoarchitecture of the facial, motor trigeminal, and ambiguus nuclei was abnormal in SRK, especially in the lateral cell group of the facial nucleus and the compact formation of the ambiguus nucleus. To examine whether orofacial motoneurons are also malpositioned in the SRK rat, horseradish peroxidase (HRP) was injected into the facial, masticatory, and abdominal esophageal muscles of the SRK rats and normal controls to label facial, trigeminal, and ambiguus motoneurons, respectively. HRP-labeled facial, trigeminal, and ambiguus motoneurons of the SRK rat were distributed more widely than those of their normal counterparts, as in the case of the reeler mouse, with the one exception that labeled facial motoneurons innervating the nasolabial muscle were distributed more widely in the ventrolateral-to-dorsomedial direction in comparison with those of the reeler mutant. These data demonstrate that nonlaminated structures in the brainstem of the SRK rat are affected severely, as is the case in the reeler mutant mouse.

Nonadrenergic innervation of the rat laryngeal vasculature

In order to gain a better understanding of the central and local control of laryngeal blood flow, the vascular innervation to the rat laryngeal muscles was examined. To visualize the vascular network, the animals were perfused with a gelatin/India ink solution. The larynges were removed and fixed. The superior laryngeal, cricothyroid, and inferior laryngeal arteries (all branch off the superior thyroid artery) were dissected in continuity into their respective muscles. Specimens were reacted in toto using immunohistochemical techniques for the presence of neuropeptide-Y (NPY), vasoactive intestinal peptide (VIP), calcitonin gene related peptide (CGRP), and neuronal nitric oxide synthase (NOS-1). Results show that all of the laryngeal vasculature is richly innervated by fibers containing these peptides. Qualitatively, the most prominent of these is NPY in association with the superior and the inferior laryngeal arteries, followed by VIP and NOS-1, and finally CGRP distributed equally on all the vessels. Immunopositive fibers are found along the entire course of the feeding arteries, beginning with the superior thyroid artery and continuing down to small arterioles into the terminal vascular beds. These peptides can act as vasodilators, vasoconstrictors, and/or neuromodulators and may work synergistically or antagonistically with other transmitters in controlling laryngeal blood flow. Their effects are dependent on the specific vascular bed in question, that is, in some areas they are vasodilators, in others vasoconstrictors, and in other neuromodulators. What effects they have on the laryngeal vasculature and how they interact within the larynx have yet to be determined.

Brainstem viscerotopic organization of afferents and efferents involved in the control of swallowing

Cholera toxin horseradish peroxidase (CT-HRP), a sensitive antegrade and retrograde tracer, is effective at labeling swallowing motoneurons and their dendritic fields within the nucleus ambiguus (NA), nucleus of the solitary tract (NTS), dorsal motor nucleus of the vagus nerve, and hypoglossal nucleus. Using this tracer to label motoneurons within the NTS demonstrates that palatal, pharyngeal, and laryngeal afferents overlap considerably within the interstitial and intermediate subnuclei. These afferents have a pattern of distribution within the NTS similar to the labeling observed after application of the same tracer to the superior laryngeal nerve. Esophageal afferents, however, terminate entirely within the central (NTScen) subnucleus and do not overlap their distribution with palatal, pharyngeal, or laryngeal afferents. Within the nodose ganglion (NG), sensory neurons projecting to the soft palate and pharynx are located superiorly, and those projecting to the esophagus and stomach are located inferiorly, an organization that indicates rostrocaudal positioning along the alimentary tract. Sensory neurons within the NG and NTS contain, among others, the major excitatory and inhibitory amino acid neurotransmitters glutamate (Glu) and gamma-aminobutyric-acid (GABA). Both Glu and GABA help to coordinate esophageal peristalsis. Using pseudorabies virus as a transsynaptic tracer demonstrates the role of GABA and Glu as mediators of synaptic transmission within the swallowing central pattern generator, a fact further supported by the presence of specific receptors for each neurotransmitter within the NTScen. Anatomic studies using CT-HRP have been effective in revealing the total extent of extranuclear dendritic projections and the organization of dendrites within the confines of a nucleus; further studies have produced the following data. Motoneurons innervating the soft palate, pharynx, larynx, and cervical esophagus have extensive dendrites that extend into the adjacent reticular formation with a distinct pattern for each muscle group. Motoneurons of the musculature active during the buccopharyngeal phase of swallowing (soft palate, pharynx, cricothyroid, and cervical esophagus) have extensive dendritic arborizations that terminate within the adjacent reticular formation of the NA. Swallowing premotor neurons located in the reticular formation surrounding the NA are active during the buccopharyngeal phase of swallowing. These data provide an anatomic basis for interaction of swallowing motoneurons with premotor neurons located in this area. Motoneurons innervating all levels of the esophagus are confined to the compact formation (NAc), whereas those motoneurons projecting to the pharynx and cricothyroid muscle are located in the semicompact formation (NAsc). The intrinsic laryngeal muscles were represented within the loose formation (NAI) and the heart within the external formation. In contrast, the dendrites of motoneurons projecting to the thoracic and subdiaphragmatic esophagus are confined to the NAc. Both the NAsc and NAc have extensive longitudinal bundling of dendrites within the confines of the nucleus, resulting in the formation of a rostrocaudal dendritic plexus where dendrites crisscross between bundles. Intranuclear bundling of dendrites is evident in the soft palate, pharynx, and esophagus and is lacking only for the cricothyroid muscle. Moreover, ventrolateral- and dorsomedial-oriented dendritic bundles are present within the NAsc. In contrast to the longitudinal dendritic bundles, the ventrolateral- and dorsomedial-oriented dendritic bundles exit the NAsc and penetrate the adjacent reticular formation. The extensive bundling of motoneuronal dendrites within the NA supports the hypothesis that these structures serve as networks for the generation of complex motor activities, such as swallowing.

Neurotransmitters and neuromodulators involved in laryngeal innervation

The distribution and role of neurotransmitters and neuromodulators in laryngeal innervation are reviewed, and our recent findings regarding the nitrergic innervation of the larynx are demonstrated for the better understanding of the complexity of the laryngeal innervation system. Noradrenergic innervation of the larynx was studied with fluorescence histochemistry and electron microscopy after application of 5-hydroxydopamine. These studies confirmed the existence of noradrenergic innervation for the submucosal glands and blood vessels, and the origin and course of noradrenergic nerve fibers contained in the laryngeal nerves and their destinations in the larynx. Cholinergic innervation of the larynx has not been clarified in detail. Many kinds of neuropeptides have been demonstrated to be involved in laryngeal innervation. Vasoactive intestinal polypeptide originating from intralaryngeal ganglionic neurons participates in laryngeal vasodilation and reduction of laryngeal seromucous secretion. Neuropeptide Y nerve fibers are few in the larynx, and most originate from the superior cervical ganglion. They are distributed around the large or medium-sized blood vessels, especially arteries. They are also associated with excretory structures. Substance P was the first neuropeptide found to be a sensory neurotransmitter in the laryngeal afferent system. It is also involved in regulation of laryngeal blood flow and secretion. Calcitonin gene-related peptide is associated with the sensory, autonomic, and motor innervation of the larynx. The majority of enkephalin nerve fibers are located close to excretory structures, although no information on the physiological significance of enkephalin is available. In addition to the above neuropeptides, the peptides histidine isoleucine, histidine methionine, and helospectin have been shown to exist in the larynx. The nitrergic innervation of the larynx has been recently studied with NADPH-diaphorase histochemistry and immunohistochemistry using antiserum against nitric oxide synthase. Nitric oxide originates from the neurons in the intralaryngeal ganglia and is believed to modulate blood flow and secretion of the larynx. It controls the laryngeal exocrine secretion in cooperation with intrinsic vasoactive intestinal polypeptide and/or extrinsic calcitonin gene-related peptide. Nitric oxide from the nodose ganglion may modulate nociception of the larynx. The existence of nitrergic neurons located in the intrinsic laryngeal muscles has been demonstrated. Many of them are bipolar or pseudounipolar, so they might be sensory in nature. The effect of injury of the recurrent laryngeal nerve on the induction of nitric oxide synthase in the laryngeal motoneurons is also discussed.

Calcitonin gene-related peptide-like immunoreactive motoneurons innervating the canine intrinsic laryngeal muscles

The percentage of calcitonin gene-related peptide (CGRP)-immunoreactive motoneurons in the nucleus ambiguus innervating the intrinsic laryngeal muscles of colchicine-treated dogs was examined by using cholera toxin B subunit-gold (CTBG) as a retrograde tracer and by immunohistochemistry. Neurons that were labeled with CTBG from the cricothyroid muscle were located in the ventromedial division of the rostral part of the nucleus ambiguus, and the ratio of CGRP-positive neurons was 93.0%. Neurons labeled with CTBG from the thyroarytenoid muscle were located in the dorsal division of the medial part of the nucleus ambiguus, and the percentage of neurons with CGRP was 71.4%. Neurons labeled with CTBG from the posterior cricoarytenoid muscle were located in the ventral division of the medial part of the nucleus ambiguus, and the percentage of CGRP-positive neurons was 85.5%. These findings suggest that the innervation and/or the neurotrophic mechanism involving CGRP for each intrinsic laryngeal muscle is different.

Ambiguus nucleus neurons innervating the abdominal esophagus are malpositioned in the reeler mouse

To examine whether the migration of ambiguus nucleus (NA) neurons is affected in the reeler mouse, recombinant replication-deficient adenoviral vector carrying E. coli-galactosidase gene (lacZ) was injected into the abdominal esophagus of the reeler mouse and normal control at two months of age prior to 5 days of sacrifice of the animals. In the normal control, lacZ-positive neurons were found in the compact formation of the NA, whereas, in the reeler, they were scattered from the base of the fourth ventricle to the ventro-lateral margin of the medulla. The present study confirmed that NA neurons are malpositioned in the reeler mouse, suggesting that the migration of NA neurons is guided by the reelin-related protein (Reelin).

Distribution of nitric oxide synthase in the esophagus of the cat and monkey

The distribution of nitrergic neurons and processes in the esophagus of the cat and monkey was studied by light microscopic immunocytochemistry using a specific antibody against purified rat brain nitric oxide synthase and immunoperoxidase procedures. Immunoreactive nerve fibers were found pervading the myenteric plexus, submucous plexus and plexus of the muscularis mucosae, and particularly in the lower esophagus a few immunoreactive fibers entered the epithelium as free nerve endings, some of which derived from perivascular fibers. In the upper esophagus immunoreactive motor end-plates were found in the striated muscle. Thirty-forty-five percent of neuronal cell bodies found in the intramural ganglia and along the course of nerve fiber bundles were immunoreactive and were of the three morphological types earlier described. In the intramural ganglia immunoreactive nerve fibers formed a plexus in which varicose nerve terminals were in close relation to immunoreactive and non-immunoreactive neurons. The intramural blood vessels that crossed the different layers of the esophageal wall were surrounded by paravascular and perivascular plexuses containing immunoreactive nerve fibers. The anatomical findings suggest that nitric oxide is involved in neural communication and in the control of peristalsis and vascular tone in the esophagus. In the lower esophagus a few nitrergic nerve fibers are anatomically disposed to subserve a sensory-motor function.

Solitarial premotor neuron projections to the rat esophagus and pharynx: implications for control of swallowing

BACKGROUND & AIMS

The buccopharyngeal and esophageal phases of swallowing are controlled by distinct networks of premotor neurons localized in the nucleus tractus solitarius. The neuronal circuitry coordinating the two phases was investigated using a combination of central and peripheral tracing techniques.

METHODS

Using pseudorabies virus, a transsynaptic tracer, in anesthetized rats, third-order esophageal neurons (neurons projecting to premotor neurons) were identified. In a separate protocol that combined transsynaptic and retrograde fluorescent tracing, third-order esophageal neurons projecting to pharyngeal motoneurons (buccopharyngeal premotor neurons) were then identified.

RESULTS

Third-order esophageal neurons were identified in the interstitial and intermediate subnuclei of the nucleus tractus solitarius and in other medullary, pontine, midbrain, and forebrain nuclei. A subpopulation of these neurons (double labeled) in the interstitial and intermediate subnuclei were found to project to pharyngeal motoneurons (buccopharyngeal premotor neurons) and to be linked synaptically to esophageal premotor neurons.

CONCLUSIONS

The synaptic link between buccopharyngeal and esophageal premotor neurons provides an anatomic pathway for the central initiation of esophageal peristalsis and its coordination with the pharyngeal phase of swallowing. This neural circuitry within the nucleus tractus solitarius is consistent with a complex central control mechanism for the swallowing motor sequence that can function independently of afferent feedback.

Discrete subregions of the rat midbrain periaqueductal gray project to nucleus ambiguus and the periambigual region

We investigated the organization of projections from the rat midbrain periaqueductal gray to nucleus ambiguus and the periambigual region using retrograde and anterograde tract tracing techniques. Retrograde tracing results revealed that neurons that project to nucleus ambiguus arise from three discrete, longitudinally organized columns of neurons located in the supraoculomotor central gray, lateral and ventrolateral periaqueductal gray. Anterograde tracing studies demonstrated that projections from these three columns of periaqueductal gray neurons terminate with topographic specificity in nucleus ambiguus and the periambigual region. Double-labelling studies demonstrated that periaqueductal gray neurons terminate in close contiguity to cholinergic neurons in the compact, semicompact, loose and external formations of nucleus ambiguus. The present results suggest that projections from periaqueductal gray to nucleus ambiguus may mediate, in part, certain cardiovascular adjustments and vocalizations produced by stimulation of periaqueductal gray.

Direct synaptic projections to esophageal motoneurons in the nucleus ambiguus from the nucleus of the solitary tract of the rat

Neurons of the nucleus of the solitary tract (NTS) serve as interneurons in swallowing. We investigated the synaptology of the terminals of these neurons and whether they project directly to the esophageal motoneurons in the compact formation of the nucleus ambiguus (AmC). Following wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) injection into the NTS, many anterogradely labeled axodendritic terminals were found in the neuropil of the AmC. The majority of labeled axodendritic terminals (89%) contained round vesicles and made asymmetric synaptic contacts (Gray's type I), but a few (11%) contained pleomorphic vesicles and made symmetric synaptic contacts (Gray's type II). More than half of the labeled terminals contacted intermediate dendrites (1-2 microm diameter). There were no retrogradely labeled medium-sized motoneurons, but there were many retrogradely labeled small neurons having anterogradely labeled axosomatic terminals. A combined retrograde and anterograde transport technique was developed to verify the direct projection from the NTS to the esophageal motoneurons. After the esophageal motoneurons were retrogradely labeled by cholera toxin subunit B conjugated HRP, the injection of WGA-HRP into the NTS permitted ultrastructural recognition of anterogradely labeled axosomatic terminals contacting directly labeled esophageal motoneurons. Serial sections showed that less than 20% of the axosomatic terminals were labeled in the esophageal motoneurons. They were mostly Gray's type I, but a few were Gray's type II. In the small neurons, more than 30% of axosomatic terminals were labeled, which were exclusively Gray's type I. These results indicate that NTS neurons project directly not only to the esophageal motoneurons, but also to the small neurons which have bidirectional connections with the NTS.

Ultrastructural characterization of pharyngeal and esophageal motoneurons in the nucleus ambiguus of the rat

The viscerotopic organization of the upper alimentary tract has been established in the nucleus ambiguus, but there is little information about the morphology of the individual neurons innervating the pharynx and esophagus. We studied the ultrastructure of pharyngeal (PH), cervical esophageal (CE), and subdiaphragmatic esophageal (SDE) motoneurons labeled by retrogradely transported wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) in the compact formation of the nucleus ambiguus. WGA-HRP was injected into the lower pharynx, or the cervical and subdiaphragmatic esophagus of male rats. The retrogradely labeled PH neurons in the rostral portion of the compact formation were large (26.1 x 50.1 microns, 906.7 microns2), polygonal, and contained well-developed cell organelles with a round nucleus. Subsurface cisterns connected with rough endoplastic reticulum were often present near the postsynaptic membrane. Both CE and SDE neurons in the compact formation were medium-sized, round or oval, and contained well-developed cell organelles, although the SDE neuron was significantly larger than the CE neuron (24.9 x 33.6 microns, 593.0 microns2 in the SDE neuron, and 19.5 x 30.2 microns, 440.3 microns2 in the CE neuron). The average number of axosomatic terminals in a sectional plane was largest in PH neurons (29.0), smaller in CE neurons (7.9), and smallest in SDE neurons (4.2). The number of axosomatic terminals containing round vesicles (Gray's type I) was almost equal to that of terminals containing pleomorphic vesicles (Gray's type II) in PH and CE neurons, but there were few Gray's type II axosomatic terminals in SDE neurons. Desmosome-like junctions at somato-somatic or somato-dendritic apposition were often present in the area surrounding SDE neurons. There were also small unlabeled neurons (9.5 x 18.1 microns, 131.8 microns2) in the compact formation of the nucleus ambiguus. The small neurons contained poorly developed cell organelles and an irregular shaped nucleus with invaginated nuclear membrane, and had no Nissl bodies. These results indicate that PH neurons have the characteristics of somatic motoneurons, and that CE and SDE neurons are similar to visceral motoneurons.

Distribution of bombesin-like immunoreactivity in the nucleus of the solitary tract and dorsal motor nucleus of the rat and human: colocalization with tyrosine hydroxylase

Bombesin is a peptide neurotransmitter/neuromodulator with important autonomic and behavioral effects that are mediated, at least in part, by bombesin-containing neurons and nerve terminals in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (DMV). The distribution of bombesin-like immunoreactive nerve terminals/fibers and cell bodies in relation to a viscerotopically relevant subnuclear map of this region was studied by using an immunoperoxidase technique. In the rat, bombesin fiber/terminal staining was heavy in an area that included the medial subnucleus of the NTS and the DMV over their full rostral-caudal extent. Distinctly void of staining were the gelatinous, central, and rostral commissural subnuclei and the periventricular area of the NTS, regions to which gastric, esophageal, cecal, and colonic primary afferents preferentially project. The caudal commissural and dorsal subnuclei had light bombesin fiber/terminal staining, as did the intermediate, interstitial, ventral, and ventrolateral subnuclei. With colchicine pretreatment, numerous cell bodies were stained in the medial and dorsal subnuclei, with fewer neurons in the caudal commissural, intermediate, interstitial, ventral, and ventrolateral subnuclei. Bombesin-like immunoreactive neurons were found in numerous other areas of the brain, including the ventrolateral medulla, the parabrachial nucleus, and the medial geniculate body. In the human NTS/DMV complex, the distribution of bombesin fiber/terminal staining was very similar to the rat. In addition, occasional bombesin-like immunoreactive neurons were labeled in a number of subnuclei, with clusters of neurons labeled in the dorsal and ventrolateral subnuclei. Double immunofluorescence studies in rat demonstrated that bombesin colocalizes with tyrosine hydroxylase in neurons in the dorsal subnucleus of the NTS. Bombesin does not colocalize with tyrosine hydroxylase in any other location in the brain. In conclusion, the distribution of bombesin in the NTS adheres to a viscerotopically relevant map. This is the anatomical substrate for the effects of bombesin on gastrointestinal function and satiety and its likely role in concluding a meal. The anatomic similarities between human and rat suggest that bombesin has similar functions in the visceral neuraxis of these two species. Bombesin coexists with catecholamines in neurons in the dorsal subnucleus, which likely mediate, in part, the cardiovascular effects of bombesin.

Extensive projections from the midbrain periaqueductal gray to the caudal ventrolateral medulla: a retrograde and anterograde tracing study in the rat

We investigated the innervation of the caudal ventrolateral medulla by the midbrain periaqueductal gray in the rat using retrograde and anterograde tract-tracing. Iontophoretic injection of Fluoro-Gold or cholera toxin B subunit into the caudal ventrolateral medulla resulted in retrogradely labeled neurons in discrete regions of the periaqueductal gray. These labeled cells were observed throughout the rostrocaudal extent of the periaqueductal gray and were distributed (as percentage of total labeled cells) in its lateral (53-67%), ventrolateral (14-28%), ventromedial (7-16%) and dorsomedial aspects (7-10%). About 70-72% of labeled cells were found in the caudal half of the periaqueductal gray and 28-30% in the rostral half. In the ventromedial periaqueductal gray, more labeled cells were seen in the contralateral side (5-13%) than the ipsilateral side (2-3%), whereas for other periaqueductal gray areas labeling was preferentially ipsilateral. Phaseolus vulgaris leucoagglutinin anterograde tracing was used to confirm the retrograde labeling results. Following iontophoretic injection into the periaqueductal gray, labeled fibers and terminals were observed throughout the rostrocaudal extent of the caudal ventrolateral medulla. Injections in the lateral and/or ventrolateral aspect of the periaqueductal gray yielded more anterograde labeling in the ipsilateral than the contralateral caudal ventrolateral medulla, while injections in the ventromedial aspect of the periaqueductal gray produced labeling preferentially in the contralateral caudal ventrolateral medulla. The present study indicates that specific regions of the periaqueductal gray project to the caudal ventrolateral medulla and may regulate cardiovascular and respiratory functions through these connections.

Influence of peripheral targets on the expression of calcitonin gene-related peptide immunoreactivity in rat cranial motoneurones

Calcitonin gene-related peptide-like immunoreactivity (CGRP-ir) is displayed by motoneurons that innervate striated muscle but is absent from preganglionic parasympathetic motoneurons. One hypothesis to explain this is that CGRP gene expression in motoneurons is, in part, dependent on influences from the innervated organ. To test this hypothesis, we cross-anastomosed the right hypoglossal and cervical vagal nerves of rats so that the vagal motoneurons grew to innervate the musculature of the tongue. Following a recovery period of 17 to 52 weeks, the distribution of CGRP-ir in the dorsal motor vagal nucleus was determined in both cross-anastomosed animals and self-anastomosed control animals. Successful reinnervation of the tongue musculature by vagal motoneurons was demonstrated by showing that electrical stimulation of the central vagus/peripheral hypoglossal nerve produced a twitch of the tongue muscles. Motoneurones of the dorsal motor vagal nucleus, which now innervated the tongue were found to express CGRP-ir, which was evident from the double labeling of neurons with both horseradish peroxidase and CGRP-ir. Motoneurones of the dorsal motor vagal nucleus contralateral to the cross-anastomosis remained CGRP negative. Similarly, motoneurons of the dorsal motor vagal nucleus in control animals where the vagus nerve was self-anastomosed remained CGRP negative, showing that an induction of CGRP expression is not a result of nerve section itself. We suggest that a signal from the striated muscle transported retrogradely via the motor axon regulates expression of CGRP-ir in motoneurons.

Transsynaptic localization of pharyngeal premotor neurons in rat

We determined the anatomy and connectivity of the brainstem circuit controlling the buccopharyngeal phase of swallowing, using pseudorabies virus to identify linked circuits of neurons. Pharyngeal vagal afferents terminate on premotor neurons in the interstitial and intermediate subnuclei of the nucleus of the solitary tract, which in turn, innervate pharyngeal motoneurons in the semicompact subnucleus of the nucleus ambiguus. This circuit is separate and distinct from the esophageal swallowing circuit.

Ultrastructure and synaptology of the nucleus ambiguus in the rat: the compact formation

The fine structure of the esophagomotor compact formation of the nucleus ambiguus was studied. Esophageal motoneurons are atypical in that they have extensive direct somato-somatic and somato-dendritic appositions without intervening glial processes. A unique feature is the presence of finger- and leaf-like somatic protrusions which partially wrap longitudinally oriented dendrites and, occasionally, small groups of dendrites and axons. The neuropil contains many longitudinally oriented, small-diameter dendrites of relatively uniform size (1.1 +/- 0.4 S.D. micrograms in diameter). Motoneuronal somatic profiles have 0-5 synapses per profile which represents a synaptic density of 10.6 synapses per soma. Axodendritic synapses measure 0.5 x 0.7 microgram in the transverse plane and are up to 3.0 micrograms long in the sagittal plane. Many axon terminals contact both a soma and dendrite in close apposition. Most axon terminals (> 90%) contain round vesicles and form asymmetric junctions with somata and dendrites. Axon terminal degeneration after electrolytic lesions and labelling after injection of wheat germ agglutinin-horseradish peroxidase in the nucleus of the tractus solitarius show that afferent connections to the compact formation form axodendritic synapses. The ultrastructure and synaptology of esophageal motoneurons is characterized by the close apposition of somata and dendrites (somatic-dendritic bundling), and the longitudinal orientation of dendrites (dendritic bundling), axons and axon terminals in the neuropil. These features may be important morphological substrates for synchronization and coordination of esophageal motoneuronal activity and esophageal peristalsis.

Expression and localization of the cystic fibrosis transmembrane conductance regulator mRNA and its protein in rat brain

In previous studies we have characterized the expression of the cystic fibrosis transmembrane conductance regulator (CFTR) protein in clathrin-coated vesicles derived from bovine brain and in neurons of rat brain. In this study we have further characterized the expression of the CFTR protein mRNA and protein in rat brain with reverse transcriptase polymerase chain reaction amplification (RT-PCR), in situ hybridization, and immunocytochemistry. The expression of CFTR mRNA and protein in discrete areas of brain, including the hypothalamus, thalamus, and amygdaloid nuclei, which are involved in regulation of appetite and resting energy expenditure, is identical. The presence of CFTR in neurons localized to these regions of brain controlling homeostasis and energy expenditure may elucidate the pathogenesis of other nonpulmonary and gastrointestinal manifestations which commonly are observed in children with cystic fibrosis. Dysregulation of normal neuropeptide vesicle trafficking by mutant CFTR in brain may serve as a pathogenic mechanism for disruption of homeostasis.

Galanin-immunoreactive nerve terminals innervating the striated muscle fibers of the rat esophagus

Galanin (GAL) immunohistochemistry combined with acetylcholinesterase (AChE) histochemistry was applied to demonstrate the innervation of the rat esophageal muscle coats. GAL immunoreactivity was found in a number of nerve cell bodies in the myenteric ganglia and in numerous varicose and non-varicose nerve fibers in the myenteric plexus and around blood vessels. Many GAL-positive varicose fibers ran in the internodal strands and along the striated muscle fibers. They often ramified and terminated on the muscle fibers to form arborizing structures, which were most abundant in the thoracic portion of the esophagus. Such GAL-positive terminals were localized in most (87.7%) of AChE-reactive motor endplates on the esophageal striated muscles. Left supranodose vagotomy caused a significant decrease of the GAL-arborizing terminals on the striated muscles of the esophagus. This suggests that they are terminals of efferent fibers in the vagus nerve.

Localization of nitric oxide synthase in the brain stem neural circuit controlling esophageal peristalsis in rats

BACKGROUND/AIMS

The central subnucleus of the nucleus of the solitary tract has been implicated in central reflex control of esophageal peristalsis. This study determined the presence of nitric oxide synthase in the brain stem circuit controlling esophageal peristalsis by combining transsynaptic retrograde tract tracing with pseudorabies virus and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH) histochemistry.

METHODS

Virus was injected into the esophagus of 10 of 15 rats. After 60-63 hours, brain sections were processed for viral immunofluorescence and NADPH histochemistry.

RESULTS

Fluorescent neuronal labeling was limited to the compact formation of the nucleus ambiguus and the central subnucleus of the nucleus of the solitary tract. Most fluorescence-labeled neurons in the central subnucleus stained positively for NADPH (double labeled). In the compact formation, there were almost no double-labeled neurons; however, NADPH-stained terminals surrounded fluorescence-labeled motoneurons.

CONCLUSIONS

NO synthase is present in premotor neurons of the central subnucleus of the nucleus of the solitary tract that innervate esophageal motoneurons in the compact formation of the nucleus ambiguus. NADPH staining in both somata and terminals of esophageal premotor neurons suggests that NO is involved in neurotransmission in the central subnucleus and at the site of synaptic contact between esophageal premotor neurons and motoneurons in the compact formation of the nucleus ambiguus.

Nitrergic innervation of the rat esophagus: focus on motor endplates

Nitric oxide synthase immunocytochemistry and correlated NADPH-diaphorase histochemistry were utilized to investigate nitrergic innervation of the rat esophagus. Almost all neuronal cell bodies and fibers around blood vessels, and in submucosa and mucosa which were immunoreactive for NOS, also co-stained for NADPH-diaphorase. A combined demonstration of motor endplates with tetramethylrhodamine alpha-bungarotoxin or calcitonin gene-related peptide immunocytochemistry demonstrated a nitrergic co-innervation of striated muscle fibers in all portions of the esophagus. The proportion of endplates co-stained increased from 35% to 78% from the cervical to the abdominal portion of the esophagus. These data indicate a role for NO in neuromuscular transmission in striated muscle of the esophagus.

Innervation of the larynx, pharynx, and upper esophageal sphincter of the rat

We identified a 'semicircular' compartment of the rat thyropharyngeus muscle at the pharyngoesophageal junction and used the glycogen depletion method to determine how the fibers of this muscle (as well as all others of the pharynx and larynx) are innervated by different cranial nerve branches. The semicircular compartment appears anatomically homologous to the human cricopharyngeus muscle, an important component of the upper esophageal sphincter. While we found very little overlap in the muscle targets of the pharyngeal, superior laryngeal and recurrent laryngeal nerves within the pharynx and larynx, the semicircular muscle receives a dual, interdigitating innervation from two vagal branches: the pharyngeal nerve and a branch of the superior laryngeal nerve we call the dorsal accessory branch. After applying horseradish peroxidase to either of these two nerves, we compared the distribution and number of cells labeled in the brainstem. The dorsal accessory branch conveys a more heterogeneous set of efferent fibers than does the pharyngeal nerve, including the axons of pharyngeal and esophageal motor neurons and parasympathetic preganglionic neurons. The observed distribution of labeled motor neurons in nucleus ambiguus also leads us to suggest that the semicircular compartment is innervated by two subsets of motor neurons, one of which is displaced ventrolateral to the main pharyngeal motor column. This arrangement raises the possibility of functional differences among semicircular compartment motor neurons correlated with the observed differences in brainstem location of cell bodies.

Brain stem localization of rodent esophageal premotor neurons revealed by transneuronal passage of pseudorabies virus

BACKGROUND/AIMS

Brain stem premotor neurons control swallowing through contacts with both afferent neurons and motoneurons. The location and connectivity of premotor neurons innervating the esophagus was determined using pseudorabies virus.

METHODS

In 30 rats, viral injections were made into either the cervical or subdiaphragmatic esophagus, cricothyroid muscle, or stomach. After a 48-62-hour survival, brain sections were processed immunocytochemically for the virus.

RESULTS

Neuronal labeling was limited to the compact formation of the nucleus ambiguus for survivals of 48-54 hours. At 57-62-hour survivals, virus-labeled second-order neurons (premotor neurons) were localized to the central subnucleus of nucleus of the solitary tract. Injections in the cricothyroid muscle and stomach resulted in distinct patterns of motoneuronal labeling in the nucleus ambiguus and dorsal motor nucleus and premotor neuronal labeling in the nucleus of the solitary tract.

CONCLUSIONS

Virus-labeled premotor neurons in the nucleus of the solitary tract occurred as a result of retrograde transport of the virus from the nucleus ambiguus because no viral antigen was present in the tractus solitarius. The esophagus is controlled by a central circuit whereby esophageal vagal afferents terminate on premotor neurons in the central subnucleus that in turn innervate esophageal motoneurons in the nucleus ambiguus.

Presence of calcitonin gene-related peptide in intraepithelial nerve fibers and motor end-plates of the cat esophagus: a light and electron microscopic study

The morphology and distribution of the motor end-plates in the striated muscle and the terminal nerve fibers in the epithelium of the wall of the esophagus, which contain calcitonin gene-related peptide, were studied by light and electron microscopic immunocytochemistry, Varicose immunoreactive nerve fibers arising from the subepithelial plexus were seen to penetrate into the epithelium where they ended in terminal boutons. These nerve fibers lost their Schwann cells just at the point of penetration into the epithelium. Characteristically, the epithelial cells of the spinous layer showed prominent tonofilaments in the part of the cytoplasm in contact with the immunoreactive nerve varicosities, but membrane specializations between these structures were not observed. In the striated muscle of the esophageal wall there were small, elliptical, immunoreactive motor end-plates, which contained a small number of axonal clear vesicles and mitochondria. They were associated with relatively short and rarely branched junctional folds, reduced postjunctional surfaces and few organelles in the underlying sarcoplasm, features characteristic of the neuromuscular junctions of slow-fatiguing red muscle fibers. The two types of immunoreactive nerve endings, epithelial and muscular, presumably participate in afferent and efferent limbs respectively of the neural control of esophageal motility. The relationship between immunoreactive nerve terminals and epithelial cells in the spinous layer exhibiting prominent tonofilaments allowed us to speculate about the existence of two different patterns of reception to sensory stimuli. The intraepithelial fibers that end in the middle layer of the epithelium could be related to mechanoreceptor reflexes, while those that end in the upper layer may be related to thermoreceptor reflexes or facilitate information about the chemical and other characteristics of foods.

NADPH-diaphorase-positive nerve fibers associated with motor endplates in the rat esophagus: new evidence for co-innervation of striated muscle by enteric neurons

NADPH-diaphorase histochemistry was combined with demonstration of acetylcholinesterase and immunocytochemistry for calcitonin gene-related peptide to study esophageal innervation in the rat. Most of the myenteric neurons stained positively for NADPH-diaphorase, as did numerous varicose nerve fibers in the myenteric plexus, among striated muscle fibers, around arterial blood vessels, and in the muscularis mucosae. A majority of motor endplates (as demonstrated by acetylcholinesterase histochemistry or calcitonin gene-related peptide immunocytochemistry) were associated with fine varicose NADPH-diaphorase-positive nerve fibers. Analysis of brainstem nuclei, sensory vagal, spinal, and sympathetic ganglia in normal and neonatally capsaicin-treated rats, and comparison with anterogradely labeled vagal branchiomotor, preganglionic and sensory fibers led to the conclusion that NADPH-diaphorase-positive fibers on motor endplates originate in esophageal myenteric neurons. No association of NADPH-diaphorase-positive nerve fibers with motor endplates was found in other organs containing striated muscle. These results suggest extensive, presumably nitrergic, co-innervation of esophageal striated muscle fibers by enteric neurons. Thus, control of peristalsis in the esophagus of the rat may be more complex than hitherto assumed.

The central vagal efferent supply to the esophagus and lower esophageal sphincter of the cat

BACKGROUND

Little is known of the central efferent neurons innervating the smooth muscle esophagus. The aim of this study was to define the location of the efferent neural pathways of the brain stem swallowing mechanism in the cat, particularly those supplying the esophageal body smooth muscle.

METHODS

Fluorescent, retrogradely transported tracers were injected into the cervical striated muscle and thoracic smooth muscle segments of the esophagus and also the lower esophageal sphincter.

RESULTS

Striated muscle efferents were found in the rostral nucleus ambiguus, but approximately 8% were located in the dorsal motor vagal nucleus. Smooth muscle efferents were present in the dorsal motor vagal nucleus in two groups, one rostral and one caudal to the obex. An additional group was found in nucleus retroambiguus. Approximately 8% of the total smooth muscle efferents were present in rostral nucleus ambiguus and were lateral to the striated muscle efferents. The lower esophageal sphincter efferents had a similar distribution to the smooth muscle efferents, but the rostral concentration of cells in the dorsal motor vagal nucleus was shifted caudally.

CONCLUSIONS

Esophageal body smooth muscle motoneurons are arranged with a similar distribution to those innervating the lower esophageal sphincter but with some topographic variation.