Projections of calcitonin gene-related peptide immunoreactive neurons in the vagal ganglia of the rat

We have studied the connections of calcitonin gene-related peptide immunoreactive (CGRP-ir) sensory neurons in the ganglia of the vagus nerve. Many CGRP-ir neurons were identified in the jugular ganglion located in the cranial cavity, while fewer CGRP-ir neurons were found in the nodose ganglion located at the level of the jugular foramen. Application of Fluorogold to the cut end of the cervical vagus nerve resulted in many Fluorogold-labeled neurons in both the jugular and the nodose ganglia. Application of Fluorogold to the cut end of the subdiaphragmatic vagus nerve resulted in Fluorogold-labeled neurons mostly in the nodose ganglion with only a few labeled neurons in the jugular ganglion. Injection of Fluorogold into the heart resulted in Fluorogold-labeled neurons in both the jugular and the nodose ganglia. Double labeling combining CGRP immunohistochemistry and Fluorogold retrograde tracing showed that in cases of both the application of Fluorogold to the cut end of the cervical vagus nerve and the injection of Fluorogold into the heart, about 40% of the Fluorogold-labeled neurons in the jugular ganglion expressed CGRP-like immunoreactivity. These results indicate that many CGRP-ir neurons in the jugular ganglion innervate the cervical and thoracic visceral organs, including the heart, but only a few CGRP-ir neurons project to the abdominal visceral organs.     

Distribution of calcitonin gene-related peptide-like immunoreactivity in the medulla oblongata of the cat, in relation to choline acetyltransferase-immunoreactive motoneurones and substance P-immunoreactive fibres

The immunohistochemical distribution of calcitonin gene-related peptide (CGRP)-like immunoreactivity (ir) in the cat medulla oblongata was examined using an antiserum to rat alpha-CGRP. Comparative distributions of substance P (SP)-like and choline acetyltransferase (ChAT)-like ir were also studied on sections adjacent to those stained for CGRP, and on sections simultaneously stained for CGRP by double staining techniques. The vast majority of ChAT-ir motoneurones in somatomotor or branchiomotor cranial nuclei (of VI, VII and XII nerves) and their accessory nuclei also displayed a coarsely granular CGRP-ir, shown by electron microscopic examination to represent immunoreactive Golgi bodies. The nucleus ambiguus (IX and X nerves), a mixed branchiomotor and visceromotor nucleus, showed CGRP-ir in a lower proportion of its motoneurones, whereas the purely viseromotor dorsal motor vagal nucleus (X nerve) contained no CGRP-ir cells. A few CGRP-ir but ChAT-negative cells were seen in the ventromedial reticular formation, lateral cuneate nucleus, infratrigeminal nucleus and nucleus of the solitary tract. Coarse, often varicose CGRP-ir fibres were most prominent in the X and IX cranial nerve rootlets, the spinal tract of the V nerve and the solitary tract, and also in the V spinal nucleus and nucleus of the solitary tract. Many of these also appeared to contain SP-ir. The central patterns of CGRP and SP-ir fibres thus reflect the previously reported coexistence of these peptides in sensory afferent cells of the trigeminal and nodose ganglia. These results are consistent with a role for CGRP as a transmitter or modulator in efferents to striated muscle, sensory afferents and intrinsic neurones in the cat brain stem.     

Patterns of unit responses to visual stimuli in the cat caudate nucleus under chloralose anesthesia.

After injection of horseradish peroxidase (HRP) into the right cardiac branches of the vagus nerve in the cat, the majority of HRP-labeled neurons were located ipsilaterally in the reticular formation ventrolateral to the nucleus ambiguus. Additionally, HRP-labeled neurons were also observed within the nucleus ambiguus (Am) and the dorsal motor nucleus of the vagus nerve (DM).     

Afferent and efferent innervation of the rat esophagus

Summary The technique of retrograde labeling of nerve cells with HRP and nuclear yellow as well as transganglionic anterograde HRP-tracing of sensory projections into the CNS were used to establish the motor and sensory innervation pattern of two parts of the rat esophagus: the cervical and the abdominal segment. For comparison, also the innervation of the anterior wall of the stomach was studied.Application of HRP to the cervical part of the esophagus resulted in bilateral labeling of neurons in the nucleus ambiguns exclusively, while application of the tracer to the abdominal part was followed by labeling of cells in both the nucleus ambiguus and the dorsal motor nucleus of the vagus. Application of tracer to the wall of the stomach caused labeling of cells in the dorsal motor nucleus of the vagus exclusively. Labeling appeared always bilaterally.In all experiments there was a profuse labeling of primary afferent neurons with cell bodies in both nodose ganglia and endings in certain subnuclei of the solitary nucleus. Endings related to the cervical esophagus projected into the ventral subnuclei, projections from the abdominal esophagus were located in the ventral and medial subnuclei, those from the stomach in the medial subnucleus solely. The area postrema and the commissural nucleus received afferents from both organs, the esophagus and the stomach.Double labeling experiments with HRP and nuclear yellow provided no signs of overlap of sensory innervation areas of the sites investigated in this study. Within the wall of the esophagus no labeled intramural cells nor nerve fibers were found in sections beyond the injection sites.     

Innervation of the sacroiliac joint in rats by calcitonin gene-related peptide-immunoreactive nerve fibers and dorsal root ganglion neurons

The sacroiliac joint (SIJ) can be a source of low back pain. Calcitonin gene-related peptide (CGRP) has been reported to play a significant role in nociceptive processing. However, the occurrence of CGRP-immunoreactive (CGRP-ir) sensory nerve fibers in the SIJ has not been fully defined. The present study investigated CGRP-ir nerve fibers supplying the SIJ. CGRP-ir nerve fibers in the vicinity of the SIJ cartilage and CGRP-ir neurons in the bilateral dorsal root ganglia (DRG) were examined immunohistochemically by administering anti-CGRP antiserum to rats. The SIJ was decalcified and cut into sections, and the CGRP-ir fibers around the SIJ cartilage were counted under microscopy. In another group, fluoro-gold (F-G), a neural tracer, was injected into the SIJ from the dorsal or ventral side with dorsal or ventral denervation. The number of F-G-labeled CGRP-ir neurons was counted in individual DRG. CGRP-ir fibers were observed more frequently in the tissues adjacent to the cranial part of the SIJ surface. In the case of dorsal denervation (ventral nerve supply), the CGRP-ir neurons composed 18.2% of the F-G-labeled neurons. In the case of ventral denervation (dorsal nerve supply), the CGRP-ir neurons composed 40.9% of the F-G-labeled neurons. There was a statistically significant difference in the number of CGRP-ir neurons between the ventral and dorsal nerve supplies to the SIJ. The cranial part of the dorsal side could be the part most associated with pain in the SIJ.     

Localization in the vagal ganglia of calcitonin gene-related peptide- and calretinin-immunoreactive neurons that innervate the cervical and the subdiaphragmatic esophagus of the rat

We have determined the localization of calcitonin gene-related peptide-immunoreactive (CGRP-ir) and calretinin-ir neurons in the vagal ganglia that innervate the cervical or subdiaphragmatic esophagus. Many CGRP-ir neurons were found exclusively in the jugular ganglion located in the cranial cavity. Calretinin-ir neurons were distributed throughout the vagal ganglia. Injection of Fluorogold into the cervical esophagus resulted in many Fluorogold-labeled neurons in the jugular and nodose ganglia. Injection of Fluorogold into the subdiaphragmatic esophagus resulted in many Fluorogold-labeled neurons, with most in the nodose ganglion. In the case of Fluorogold injection into the cervical esophagus, double-labeling combining immunohistochemistry and retrograde tracing showed that about 40% of the Fluorogold-labeled neurons in the jugular ganglion express CGRP-like immunoreactivity, and about 20% of the Fluorogold-labeled neurons in both the jugular and nodose ganglia express calretinin-like immunoreactivity. In the case of injection into the subdiaphragmatic esophagus, only a few Fluorogold-labeled neurons express CGRP-like immunoreactivity or calretinin-like immunoreactivity in the vagal ganglia. These results indicate that the cervical esophagus receives projections from many CGRP-ir neurons in the jugular ganglion and from calretinin-ir neurons in the jugular and nodose ganglia, while the subdiaphragmatic esophagus receives projections from only a few CGRP-ir and calretinin-ir neurons in the vagal ganglia.     

Organization and distribution of the upper and lower esophageal motoneurons in the medulla and the spinal cord of the rat

The upper cervical esophagus is exerted on swallowing and peristalsis by somatic and visceral motoneurons, whereas the lower esophagus is exerted on only peristalsis by visceral motoneurons. We examined the origin of the esophageal motoneurons and whether there were any differences between the distributions of the upper and the lower esophageal motoneurons in the medulla and the spinal cord using cholera toxin subunit b (CTb) as the retrograde tracer. Following injection of CTb into the cervical esophagus resulted in heavy labeling of the neurons in the nucleus ambiguus including the compact (AmC), semicompact (AmS) and loose (AmL) formations, and the medial column of lamina IX at the C1-C5 levels of the cervical spinal cord corresponding to the spinal accessory nucleus. A few labeled neurons were found in the inferior salivatory nucleus, the rostral division of the dorsal motor nucleus of the vagus (DMX), the accessory facial nucleus and the lateral column of lamina IX at the C2 and C3 levels. All these labeled neurons showed ChAT immunoreactivity. When CTb was injected into the cut end of the unilateral recurrent laryngeal nerve, many labeled neurons were found in the ipsilateral AmC, the AmL, and the bilateral medial column at the C1 and C2 levels. Following injection of CTb into the subdiaphragmatic esophagus resulted in heavy labeling of the neurons only in the AmC and the DMX. When CTb was injected into the sternomastoid muscle, many labeled neurons were found in the medullary reticular formation, the facial nucleus, the medial column at the C1-C3, C5 and C6 levels, and the lateral column at the C2, C3, C5 and C6 levels. Injections of a Fluoro-Gold into the cervical esophagus and a CTb into the sternomastoid muscle or the subdiaphragmatic esophagus in the same animal showed many double labeled neurons in the medial column of the accessory nucleus at the C1 and C2 levels, but no double labeled neurons in the AmC. These results indicated that the upper cervical esophagus is innervated by the visceral medullary vagal motoneurons as well as the somatic spinal accessory motoneurons. The lower esophagus is innervated only by the visceral medullary vagal motoneurons.     

Calcitonin gene-related peptide immunoreactive sensory neurons in the vagal and glossopharyngeal ganglia innervating the larynx of the rat

We have examined whether calcitonin gene-related peptide-immunoreactive (CGRP-ir) neurons in the vagal and glossopharyngeal ganglia innervate the larynx. Many CGRP-ir neurons were located mostly in the superior glossopharyngeal–jugular ganglion complex that was fused the superior glossopharyngeal ganglion and the jugular ganglion in the cranial cavity. When Fluorogold was applied to the cut end of the superior laryngeal nerve (SLN) or the recurrent laryngeal nerve (RLN), many Fluorogold-labeled neurons were found in the superior glossopharyngeal–jugular ganglion complex and the nodose ganglion. Double-labeling for CGRP and Fluorogold showed that about 80% of Fluorogold-labeled neurons in the superior glossopharyngeal–jugular ganglion complex expressed CGRP-like immunoreactivity in the case of application to the SLN, and about 50% of Fluorogold-labeled neurons expressed CGRP-like immunoreactivity in the case of the RLN. Only a few double-labeled neurons were found in the nodose ganglion. The number of the Fluorogold-labeled neurons and double-labeled neurons in the superior glossopharyngeal–jugular ganglion complex in the case of the SLN was larger than that in the case of the RLN. These results indicate that sensory information from the larynx might be conveyed by many CGRP-ir neurons located in the superior glossopharyngeal–jugular ganglion complex by way of the SLN and the RLN.     

大鼠心脏迷走神经节前纤维的起源：HRP法研究

将辣根过氧化物酶(HRP)结晶涂于大鼠右侧迷走神经心支近侧断端,在同侧迷走神经背侧运动核、疑核以及两核之间的网状结构内发现标记细胞。根据实验结果,对心脏迷走神经节前纤维的起源进行了讨论。     

Brain-derived neurotrophic factor immunoreactive vagal sensory neurons innervating the gastrointestinal tract of the rat

We have determined whether brain-derived neurotrophic factor immunoreactive (BDNF-ir) neurons in the vagal ganglia innervate the gastrointestinal tract. Many BDNF-ir neurons were medium in size and located throughout the jugular and nodose ganglia. When Fluorogold was injected into the wall of the cervical esophagus, many retrogradely Fluorogold-labeled neurons were found in both the jugular ganglion and the nodose ganglion. When Fluorogold was injected into the body of the stomach or applied to the cut end of the subdiaphragmatic vagus nerve, numerous Fluorogold-labeled neurons were found mostly in the nodose ganglion. Double-labeling combining immunohistochemistry for BDNF and retrograde tracing with Fluorogold showed that more than 90% of the neurons in the jugular ganglion and the nodose ganglion projecting to the cervical esophagus contained BDNF-like immunoreactivity. In the cases of both Fluorogold injection into the stomach and Fluorogold application to the subdiaphragmatic vagus nerve, almost all Fluorogold-labeled neurons in the nodose ganglion contained BDNF-like immunoreactivity. These results indicated that almost all vagal sensory neurons located in either the jugular ganglion or the nodose ganglion that innervate the gastrointestinal tract are BDNF-ir neurons.     

鸡舌咽神经传出神经元在脑干的分布

目的 研究鸡舌咽神经传出神经元在脑干的分布。方法 选用13只健康来抗鸡,分离暴露舌咽神经干,在岩神经节处注射4ulCB-HRP,动物存活约35h,灌注固定,取延髓作冰冻连续切片,TMB法呈色,光镜下观察。结果 舌咽神经传出神经元主要位于舌咽神经背运动核,部分位于迷走神经背运动核的前端和面神经腹侧核。结论 鸡舌咽神经背运动核和迷走神经背运动核有相互重叠的现象,其位置与哺乳类的明显不同。     

Co-localization of choline acetyltransferase and tyrosine hydroxylase within neurons of the dorsal motor nucleus of the vagus

In the present study, we employed a dual-immunofluorescent labeling procedure to determine if the biosynthetic enzymes tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) are co-localized within neurons in the dorsal medulla of rat. Within this region TH-labeled neurons are distributed within the nuclei of the solitary tracts and medial aspect of the dorsal motor nucleus of the vagus. The absence of dopamine-beta-hydroxylase immunoreactivity within TH-labeled cells in the medial portion of the dorsal motor nucleus of the vagus suggests that these neurons are dopaminergic. Cholinergic perikarya also are present in the dorsal medulla and are distributed throughout the dorsal motor nucleus of the vagus and hypoglossal nucleus. Of these ChAT-positive perikarya, a small percentage limited to the medial aspect of the dorsal motor nucleus of the vagus (i.e., corresponding to the location of dopamine neurons) also contain TH. The existence of TH within ChAT-positive neurons in the dorsal motor nucleus of the vagus provides an anatomical substrate with which to suggest that catecholaminergic and cholinergic fibers contribute to the vagus nerve and may serve to explain some of the cardiac and gastric effects resulting from systemic administration of catecholamine agents.     

Motor neurons of the laryngeal nerves

The present study was undertaken to determine the relationship between the motor neurons of the superior and recurrent laryngeal nerves within the nucleus ambiguus. The retrograde transport of horseradish peroxidase was utilized to identify the motor neurons subsequent to its application to the proximal transected end of the superior and recurrent laryngeal nerves. Labeled superior laryngeal motor neurons were distributed ventrolaterally in the rostral portion of the nucleus. The recurrent laryngeal motor neurons were distributed throughout the nucleus with two distinct populations: a rostral group and a caudal group. The rostral group overlaps the motor neurons of the superior laryngeal nerve. The caudal group occupies that portion of the nucleus that is classically described for the recurrent laryngeal nerve. Additional superior laryngeal nerve labeled perikarya were found in the dorsal motor nucleus of the vagus. This study defines the rostral distribution of the recurrent laryngeal nerve motor neurons and suggests that this rostral group is a component of the neuroanatomical substrate that is involved in the co-activation of the laryngeal abductors controlling the laryngeal aperture.     

Motor neurons of the laryngeal nerves.

The present study was undertaken to determine the relationship between the motor neurons of the superior and recurrent laryngeal nerves within the nucleus ambiguus. The retrograde transport of horseradish peroxidase was utilized to identify the motor neurons subsequent to its application to the proximal transected end of the superior and recurrent laryngeal nerves. Labeled superior laryngeal motor neurons were distributed ventrolaterally in the rostral portion the nucleus. The recurrent laryngeal motor neurons were distributed throughout the nucleus with two distinct populations: a rostral group and a caudal group. The rostral group overlaps the motor neurons of the superior laryngeal nerve. The caudal group occupies that portion of the nucleus that is classically described for the recurrent laryngeal nerve. Additional superior laryngeal nerve labeled perikarya were found in the dorsal motor nucleus of the vagus. This study defines the rostral distribution of the recurrent laryngeal nerve motor neurons and suggests that this rostral group is a component of the neuroanatomical substrate that is involved in the co-activation of the laryngeal abductors controlling the laryngeal aperture.     

Calcitonin gene-related peptide immunoreactive neurons innervating the soft palate,the root of tongue,and the pharynx in the superior glossopharyngeal ganglion of the rat

We have examined whether calcitonin gene-related peptide immunoreactive (CGRP-ir) neurons in the glossopharyngeal ganglia innervate the soft palate, the root of tongue, and the pharynx of the rat. Immunohistochemical observations revealed that numerous CGRP-ir neurons are located in the superior glossopharyngeal ganglion located ventrolateral to the medulla oblongata in the cranial cavity, and that CGRP-ir neurons are also located in the inferior glossopharyngeal ganglion at the jugular foramen. When Fluorogold was injected into the soft palate, the root of tongue, or the pharyngeal constrictor muscles, many retrogradely Fluorogold-labeled neurons were found in the superior glossopharyngeal ganglion and the nodose ganglion, and several Fluorogold-labeled neurons were found in the inferior glossopharyngeal ganglion. Double labeling with immunohistochemistry for CGRP and Fluorogold showed that in every case of injections of Fluorogold into the soft palate, the root of tongue, or the pharynx, about 30% of the Fluorogold-labeled neurons in the superior glossopharyngeal ganglion expressed CGRP-like immunoreactivity, while no double-labeled neurons were found in the inferior glossopharyngeal ganglion or the nodose ganglion. These results indicate that nociceptive sensory information from the soft palate, the root of tongue, and the pharynx might be conveyed by the neurons in the superior glossopharyngeal ganglion to the nucleus tractus solitarii.     

Immunohistochemical mapping of natriuretic peptide receptor-A in the brainstem of Macaca fascicularis

Natriuretic peptide receptor-A (NPR-A) mediates the biological effects of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), and is involved in maintaining cardiovascular homeostasis. In this immunohistochemical study we examined the distribution of NPR-A in the brainstem of the cynomolgus monkey. NPR-A immunoreactivity was localized to neurons in specific brainstem regions. NPR-A-immunoreactive perikarya were found in the red nucleus and the oculomotor nucleus in the midbrain, the parabrachial nucleus and the locus coeruleus in the pons, and the dorsal motor nucleus of the vagus, the hypoglossal nucleus, the cuneate nucleus, the gracile nucleus, the nucleus ambiguus, the lateral reticular nucleus, the reticular formation, and the inferior olivary nucleus in the medulla oblongata. Extensive networks of immunoreactive fibers were apparent in the red nucleus, the oculomotor nucleus, the principal sensory trigeminal nucleus, and the parabrachial nucleus. Double immunostaining revealed NPR-A immunoreactivity in cholinergic neurons of the parabrachial nucleus, the dorsal motor nucleus of vagus, the hypoglossal nucleus, and the nucleus ambiguus. However, there was no colocalization of NPR-A and tyrosine hydroxylase in the locus coeruleus. The wide anatomical distribution of NPR-A-immunoreactive structures suggests that natriuretic peptides, besides having a role in the central regulation of endocrine and cardiovascular homeostasis, may also mediate diverse physiological functions.     

Distribution of mu-opioid receptors in rat visceral premotor neurons

Agonists of the mu-opioid receptor (MOR) can modulate the activity of visceral premotor neurons, including cardiac premotor neurons. Neurons in brainstem regions containing these premotor neurons also contain dense concentrations of the MOR1. This study examined the distribution of MOR1 within two populations of visceral premotor neurons: one located in the dorsal motor nucleus of the vagus and the other in the nucleus ambiguus. Visceral premotor neurons contained the retrograde tracer Fluoro-Gold following injections of the tracer into the pericardiac region of the thoracic cavity. MOR1 was localized using immunogold detection of an anti-peptide antibody. Visceral premotor neurons in both regions contained MOR1 at somatic and dendritic sites, although smaller dendrites were less likely to contain the receptor than larger dendrites, suggesting there may be selective trafficking of MOR1 within these neurons. MOR1 labeling in nucleus ambiguus neurons was more likely to be localized to plasma membrane sites, suggesting that ambiguus neurons may be more responsive to opioid ligands than neurons in the dorsal motor nucleus of the vagus. In addition, many of the dendrites of visceral premotor neurons were in direct apposition to other dendrites. MOR1 was often detected at these dendro-dendritic appositions that may be gap junctions. Together these findings indicate that the activity of individual visceral premotor neurons, as well as the coupling between neurons, may be regulated by ligands of the MOR.     

Galanin inhibits gut-related vagal neurons in rats

Galanin plays an important role in the regulation of food intake, energy balance, and body weight. Many galanin-positive fibers as well as galanin-positive neurons were seen in the dorsal vagal complex, suggesting that galanin produces its effects by actions involving vagal neurons. In the present experiment, we used tract-tracing and neurophysiological techniques to evaluate the origin of the galaninergic fibers and the effect of galanin on neurons in the dorsal vagal complex. Our results reveal that the nucleus of the solitary tract is the major source of the galanin terminals in the dorsal vagal complex. In vivo experiments demonstrated that galanin inhibited the majority of gut-related neurons in the dorsal motor nucleus of the vagus. In vitro experiments demonstrated that galanin inhibited the majority of stomach-projecting neurons in the dorsal motor nucleus of the vagus by suppressing spontaneous activity and/or producing a fully reversible dose-dependent membrane hyperpolarization and outward current. The galanin-induced hyperpolarization and outward current persisted after synaptic input was blocked, suggesting that galanin acts directly on receptors of neurons in the dorsal motor nucleus of the vagus. The reversal potential induced by galanin was close to the potassium ion potentials of the Nernst equation and was prevented by the potassium channel blocker tetraethylammonium, indicating that the inhibitory effect of galanin was mediated by a potassium channel. These results indicate that the dorsal motor nucleus of the vagus is inhibited by galanin derived predominantly from neurons in the nucleus of the solitary tract projecting to the dorsal motor nucleus of the vagus nerve. Galanin is one of the neurotransmitters involved in the vago-vagal reflex.     

鸡迷走神经传出神经元及其突起的分布

用10只约一年龄的白色来杭鸡,将CB-HRP7μl注入颈部迷走神经干内,动物存活48小时,经主动脉弓处灌流固定。取延髓作40μl厚的冰冻连续切片,TMB法成色。光镜观察。标记的神经元主要位于廷髓的迷走神经背核、疑核及中间带。迷走背核及疑核中的树突都呈放射状分布到周围几个方向。     

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

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