Brain stem projections of sensory and motor components of the vagus complex in the cat: II. Laryngeal, tracheobronchial, pulmonary, cardiac, and gastrointestinal branches

A comparison of the distribution of central cholinergic neurons as demonstrated by acetylcholinesterase pharmacohistochemistry and choline acetyltransferase immunohistochemistry

The topographical distribution of cholinergic cell bodies has been studied in the rat brain and spinal cord by choline acetyltransferase (ChAT)-immunohistochemistry and acetylcholinesterase (AChE)-pharmacohistochemistry using diisopropylfluorophosphate (DFP). The ChAT-containing cells and the cells that stained intensely for AChE 4-8 hr after DFP were mapped in detail on an atlas of the forebrain (telencephalon, diencephalon) hindbrain (mesencephalon, rhombencephalon) and cervical cord (C2, C6). Striking similarities were observed between ChAT-positive cells and neuronal soma that stained intensely for AChE both in terms of cytoarchitectural characteristics, and with respect to the distribution of the labelled cells in many areas of the central nervous system (CNS). In the forebrain these areas include the caudatoputamen, nucleus accumbens, medial septum, nucleus of the diagonal band, magnocellular preoptic nucleus and nucleus basalis magnocellularis. In contrast, a marked discrepancy was observed in the hypothalamus and ventral thalamus where there were many neurons that stained intensely for AChE, but where there was an absence of ChAT-positive cells. No cholinergic perikarya were detected in the cerebral cortex, hippocampus, amygdala and dorsal diencephalon by either histochemical procedure. In the hindbrain, all the motoneurons constituting the well-established cranial nerve nuclei (III-VII, IX-XII) contained ChAT and exhibited intense staining for AChE. Further, a close correspondence was observed in the distribution of labeled neurons obtained by the two histochemical procedures in the midbrain and pontine tegmentum, including the laterodorsal tegmental nucleus, some areas in the caudal pontine and bulbar reticular formation, and the central gray of the closed medulla oblongata. On the other hand, AChE-intense cells were found in the nucleus raphe magnus, ventral part of gigantocellular reticular nucleus, and flocculus of the cerebellum, where ChAT-positive cells were rarely observed. According to both techniques, no positive cells were seen in the cerebellar nuclei, the pontine nuclei, or the nucleus reticularis tegmenti pontis. Large ventral horn motoneurons and, occasionally, cells in the intermediomedial zone of the cervical cord displayed ChAT-immunoreactivity and intense AChE staining. On the other hand, AChE-intense cells were detected in the dorsal portion of the lateral funiculus, but immunoreactive cells were not found in any portion of the spinal cord white matter.(ABSTRACT TRUNCATED AT 400 WORDS)

Vagal neurons and pathways to the rat's lower viscera: an electrophysiological study

The vagal pathways to the rat's pancreas are anatomically difficult to describe. A stimulation/recording technique has been used on various segments of the vagus to trace vagal pathways to the lower viscera, and a microelectrode recording technique to locate vagal neurons of origin in the brain stem's dorsal motor nucleus (DMX). The two main pathways (right cervical vagus to dorsal celiac branch and left cervical vagus to ventral celiac branch) are supplemented by two accessory ones where each cervical vagus gives some fibers to its contralateral homologue at the diaphragmatic level. These pathways consist almost exclusively of C-fibers. Neurons of origin of the dorsal vagal trunk fibers have been identified by the collision test and occupy the caudal half of the DMX; those of the dorsal celiac branch fibers originate from the medial part of that area.

Parabrachial nuclei damage in infant rats produces residual deficits in gustatory preferences/aversions and sodium appetite

Ten-day-old rats sustained bilateral electrolytic lesions of the parabrachial nuclei in the pons (PBN). Growth measures and tests of sensorimotor, feeding and drinking behaviors, sodium appetite, and gustatory capacities were made between ages 1 and 150 days. PBN rats displayed a transient period of attenuated suckling, as evidenced by body weight loss. When tested soon after weaning, PBN rats were hyperdipsic in response to cellular dehydration and during food deprivation. This effect, however, was temporary. When tested as adults, PBN rats were hypodipsic in response to extracellular fluid volume depletion, they displayed alterations in sodium appetite, showed "exaggerated" preferences and aversions to saccharin and NaCl solutions, and they displayed attenuated quinine aversions. These results are generally similar to the behaviors of rats sustaining more central gustatory pathway lesions as adults. The functional significance of the PBN in the developing rat for preference/aversion and sodium appetite behaviors are discussed.

The location of chronotropic cardioinhibitory vagal motoneurons in the medulla of the rabbit

Vagal preganglionic motoneurons originating in nucleus ambiguus (NA) and dorsal vagal nucleus (DVN) were identified via retrograde labeling with horseradish peroxidase (HRP). DVN and NA were then explored for cardiovascular responsive sites using microstimulation. Stimulation within DVN from slightly caudal to obex to 3.00 mm rostral to obex produced a primary bradycardia (n = 15, X = -123 bpm). Stimulation within NA from slightly rostral to obex to 1.5 mm caudal to obex produced a similar primary bradycardia (n = 15, X = -127 bpm). Extracellular recordings were made from 7 cells in DVN and 10 cells in NA in regions producing maximal bradycardia to electrical stimulation. These cells were antidromically activated by cervical vagus nerve (VN) stimulation, increased their firing rates to systemic injection of phenylephrine (PE), revealed an expiratory rhythm, showed an increase in firing rate coinciding with spontaneous and elicited decreases in heart rate, had conduction velocities in the A-delta and B-fiber range, and produced bradycardia upon stimulation through the recording electrode with thresholds as low as 4 microA. The data indicate that in rabbits, chronotropic cardioinhibitory vagal motoneurons are discretely localized on the lateral, caudal portions of DVN and NA between 0.5 mm caudal and 1.5 mm rostral to obex.

Synaptic interaction of vagal afferents and catecholaminergic neurons in the rat nucleus tractus solitarius

Combined radioautography and immunocytochemistry were used to define the ultrastructure and synaptic relations between vagal sensory afferents and catecholaminergic (CA) neurons of the A2 group located within the nucleus tractus solitarius (NTS) of rat brain. The vagal afferents were radioautographically labeled by tritiated amino acids anterogradely transported from the nodose ganglion. Immunocytochemical labeling for tyrosine hydroxylase (TH) served for the identification of catecholaminergic neurons. The radiographically labeled axons seen by light microscopy were widely distributed throughout the more caudal NTS. The reduced silver grains were more densely distributed within the NTS located homolateral to the injected nodose ganglion. The radioautographically labeled processes were localized in regions containing catecholaminergic neurons as indicated by immunoreactivity for TH. Electron microscopic analysis of the medial NTS at the level of the obex demonstrated that the reduced silver grains were localized within axon terminals. The radioautographically labeled terminals were 2-3 microns in diameter, contained numerous small, clear and a few large, dense vesicles, and formed predominately axodendritic synapses. Many of the recipient dendrites contained immunoreactivity for TH. In rare instances, vagal afferents formed synaptic appositions with both TH-labeled and unlabeled axon terminals and neuronal soma. This study provides the first ultrastructural evidence that the catecholaminergic neurons within the NTS receive direct synapses from sensory neurons in the nodose ganglion.

Long descending projections of the hypothalamus in the pigeon, Columba livia

An autoradiographic analysis was performed on the descending projections of nucleus periventricularis magnocellularis (PVM) of the hypothalamus in the pigeon. A PVM-medullospinal pathway was observed coursing posteriorly through the lateral hypothalamus, ventrolateral midbrain tegmentum, and into the spinal lemniscus (ls) in the ventrolateral pons and medulla. In the pons, some fibers course dorsomedially from ls and terminate at the lateral border of the locus coeruleus. At medullary levels, fibers from ls sweep dorsomedially in the plexus of Horsley and project to certain regions of the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (NX). Specifically, PVM fibers project heavily into NTS subnuclei medialis superficialis, medialis ventralis, and lateralis (sulcalis) dorsalis as well as into the ventral parvocellular subnucleus of NX. Fibers in ls were traced caudally into the lateral funiculus as far as upper cervical levels of the spinal cord. Although autoradiographs of lower cervical or thoracic spinal cord sections were not available, PVM fibers do descend to thoracic spinal cord levels, as evidenced by the retrograde transport of horseradish peroxidase. In addition to the medullospinal pathway, the autoradiographs demonstrated PVM projections to septum, diencephalon, and midbrain. Labeled PVM fibers are found in the lateral septal nucleus, nucleus of the anterior pallial commisure, dorsomedial thalamic nucleus, dorsolateral anterior thalamic nucleus (pars ventralis), median eminence, medial and lateral hypothalamus, medial mammillary area, and nucleus intercollicularis and central gray of the midbrain. The projection of fibers to medullospinal regions and median eminence suggests that PVM is homologous to the mammalian paraventricular nucleus. These projections to specific subnuclei of NTS and NX denote hypothalamic control over certain autonomic functions.

ACTH-related peptide containing neurons within the medulla oblongata of the rat

Neurons containing antigenic determinants of 16 Kdalton fragment, ACTH, gamma-LPH, and beta-endorphin have been identified in the nucleus tractus solitarius and lateral reticular formation of the rat brainstem. Immunoreactive fibers extend longitudinally in dorsal and ventral midline tracts throughout the length of the brainstem, and are also concentrated in lateral reticular regions known to contain catecholamine nuclei. ACTH-containing neurons could participate with brainstem catecholamine cell groups in controlling visceral function.

Central connections of the sensory and motor nuclei of the vagus nerve

Recent morphological and immunohistochemical studies bearing on the central pathways involved in processing vagal afferent information and in modulating the activity of vagal preganglionic neurons are summarized. The nucleus of the solitary tract (NTS), the principal recipient of first order vagal afferent inputs, projects to preganglionic cell groups of both divisions of the autonomic nervous system, to motor nuclei of cranial nerves that supply the face and tongue, to a series of 'relay' nuclei in the brainstem, and to a number of cell groups in the hypothalamus and the limbic region of the telencephalon that integrate autonomic, neuroendocrine and regulatory behavioral responses. With the exception of the cranial nerve motor nuclei, each cell group in receipt of direct inputs from the NTS projects back to this region and/or to the vagal motor nuclei, and is thereby in a position to influence vagal motor outflow. This central vagal system is further characterized by the presence of neurons that contain an impressive diversity of neuropeptides and monoamines. Examples are cited to illustrate how biochemically specified projections within this system are organized, and how they provide potential substrates for encoding information transfer between its components.

Afferent interactions of cranial nerves involved in ingestion

Substantial behavioral evidence implicates visceral afferent activity in the regulation of feeding behavior. One mechanism often suggested for this influence involves visceral afferent activity interacting with oral or gustatory afferent activity. This brief review summarizes the anatomical and electrophysiological evidence that indicates that such interactions might in fact take place. The available evidence for interactions between visceral and gustatory afferent messages is far from convincing, but perhaps only because the issue has seldom been addressed. The most direct tests suggested by the hypothesis advanced remain to be carried out.

Nucleus tractus solitarii respiratory neurons in the chemoreceptor pathway activated by almitrine

In anaesthetized, paralysed and artificially ventilated dogs, activities were recorded from the phrenic nerve and from respiratory units within the nucleus tractus solitarii (NTS). The inspiratory neurons were classified according to their discharge pattern and their response to lung inflation. Two categories of cells with an augmenting discharge pattern were detected: the R alpha inspiratory neurons (18 units) inhibited by lung inflation and the R beta cells (10 units) activated by inflation. Prolonged stimulation of peripheral chemoreceptors by almitrine (50 micrograms/kg i.v.) induced an increase in the firing rate of R alpha and R beta inspiratory neurons. In addition almitrine stimulated R beta cells classified as expiratory-inspiratory units. Two expiratory neurons were found in the NTS and the firing rate of these cells was enhanced by almitrine. It is concluded that the NTS respiratory neurons are strongly involved in the chemoreceptor pathway activated by almitrine.

Localization of motoneurons innervating the levator veli palatini muscle in the cat

Recent investigations of the nucleus ambiguus (NA) have attempted to identify motoneurons associated with the branchiomeric muscles of the larynx and pharynx. However, relatively little attention has been directed to the levator veli palatini muscle (LVP) which is critical in respiration, deglutition and eustachian tube function. Although the consensus is that cranial nerve X (vagus) innervates this muscle, some investigators have suggested that the LVP is innervated by either cranial nerve VII (facial) or IX (glossopharyngeal). The present study was designed to identify the specific location of LVP motoneurons within the brainstem. Horseradish peroxidase (HRP) was injected into the LVP of 18 cats. Following a survival period of 24-48 hours, animals were sacrificed and tissue processed according to Mesulam's TMB procedure. HRP labeled cells were located in the rostral NA both ipsilateral and contralateral to the side of injection and in the ipsilateral retrofacial nucleus (RFN). There were no labeled cells in the facial nucleus. Innervation of the LVP by cranial nerve VII would thus be excluded. This is the first report to definitively localize LVP motoneurons. Although the innervation of LVP by cranial nerve X is generally agreed upon in basic anatomy textbooks, identification of LVP motoneurons within the NA does not exclude innervation by cranial nerve IX.

Nucleus tractus solitarius lesions block the behavioral actions of cholecystokinin

Cholecystokinin (CCK) has been implicated as a signal for the syndrome of satiety in a variety of species. Several lines of evidence point to a peripheral site of action for the behavioral effects of CCK. Peripheral CCK receptors appear to activate a gut-brain pathway involving the sensory fibers of the vagus nerve. To investigate the central anatomical substrate of this visceral-behavioral control system, the terminal regions of the sensory tract of the vagus were lesioned. Radiofrequency lesions of the nucleus tractus solitarius abolished the effects of acute doses of CCK on exploratory behaviors. Sham lesions had no effect on baseline exploratory behaviors and did not influence the ability of CCK to decrease spontaneous exploratory behaviors. These findings delineate the first central site along the ascending sensory pathway which appears to mediate the satiety-related behavioral effects of CCK.

Visceral representation within the nucleus of the tractus solitarius in the pigeon, Columba livia

This study describes the distribution of organ-specific populations of vagal afferent fibers within the nucleus of the solitary tract (nTS) in the pigeon. The central projections of vagal sensory neurons were visualized by the centripetal and trans-ganglionic transport of horseradish peroxidase from either the central cut ends of peripheral vagal branches or from HRP injection sites in peripheral vagal target tissues. This paper also includes a detailed description of the cytoarchitectural organization of the nTS in the pigeon based on studies of Nissl-stained material. Vagal afferent fibers that innervate different peripheral target organs are partially segregated within cytoarchitecturally distinct subnuclei of the nTS. Gastrointestinal afferents, for example, project primarily to medial subnuclei. On the other hand, pulmonary, and on the basis of earlier studies, cardiovascular afferents, project primarily to lateral subnuclei. Moreover, the rostral to caudal distribution of gastrointestinal afferents corresponds to the rostrocaudal topography of the gastrointestinal tract. In addition, our data demonstrate a projection of gastrointestinal afferents to the lateral descending tract of the trigeminal nerve that appears to terminate in the external cuneate nucleus. The cytoarchitectural organization of visceral representations within the pigeon nTS corresponds closely to recent descriptions of this cell group in mammals. Comparison of our results with studies of the central connections of nTS neurons suggests that the subnuclear distribution of organ-specific vagal afferents within nTS plays a critical role in the organization of ascending and descending visceral afferent pathways.

The afferent and preganglionic parasympathetic innervation of the rat liver, demonstrated by the retrograde transport of horseradish peroxidase

The afferent and parasympathetic preganglionic innervations of the rat liver were investigated by the use of retrograde transport of horseradish peroxidase (HRP). Vagal nerve fibers reach the rat liver by way of the left and right hepatic nerves, which originate from the homonimous abdominal vagal trunks. Three different experimental protocols were used: (i) intraparenchymal HRP injections; (ii) retrograde HRP injection through the common bile duct; (iii) HRP application to the central end of the severed hepatic nerves. The technical problems inherent in these 3 methods were experimentally investigated, with regard to the possible leakage of HRP from the liver after retrograde injection. It is concluded that leakage of HRP occurs, but it is not sufficient to cause non-specific labeling. Neurons of the lower thoracic dorsal root ganglia (DRG) are bilaterally labeled following intraparenchymal and retrograde HRP injections. Bilateral labeling of the nodose ganglia (NGs) following retrograde injection is still observed after subdiaphragmatic section of the left abdominal vagus, whereas cervical transection prevents labeling of the ipsilateral NG. Labeling produced by exposure of the left hepatic nerve to HRP is prevented by subdiaphragmatic transection of the left abdominal vagus. Efferent neurons located bilaterally in the dorsal motor nucleus (DMN) and in the left nucleus ambiguus (NA) are labeled following retrograde HRP injection. Only ipsilateral labeling is observed after HRP application to the cut left hepatic nerve. HRP exposure of the left abdominal vagus yields bilateral labeling in both DMN and NA. It is concluded that: (i) the afferent innervation of the rat liver is provided by the lower thoracic DRG and by the NGs of both vagi, mostly by the left; partial crossing of vagal afferent fibers takes place at thoracic level; and (ii) the liver receives efferent fibers bilaterally from the DMN and from the left NA; the DMN neurons project to the liver via the homolateral hepatic nerves, and those of the NA via the left hepatic nerve.

Subnuclear organization of the dorsal motor nucleus of the vagus nerve in the pigeon, Columbia livia

The present study is the first of two papers describing the cytoarchitectural and functional organization of the dorsal motor nucleus of the vagus nerve (DMN complex) in the pigeon. This paper describes the distribution of vagal motoneurons within the pigeon brainstem, and the cytoarchitectural organization of the DMN complex. Our description is based on studies of Nissl-stained tissue from normal animals and on experimental studies using retrograde tracing techniques. Cells within the DMN complex were classified according to size, morphology, location, and staining characteristics. These studies demonstrate that vagal motoneurons are localized to (1) the DMN complex, (2) the region of the nucleus ambiguus, and (3) the region of the reticular formation extending between the dorsal motor nucleus and the nucleus ambiguus. Our cytoarchitectural indicate that the DMN complex is composed of at least 11 cytoarchitecturally distinct subnuclei. These subnuclei are evident in normal tissue and are especially prominent in cases where HRP backfilling produces a Golgi-like staining of the motoneurons. The subnuclei can be distinguished by their positions within the DMN complex and by the size, shape, and staining characteristics of their constituent neurons. Comparison of these data with studies in other species indicates similar patterns of cytoarchitectural organization in the DMN complex of some mammals. The diversity of nuclear subgroups within the DMN complex may be related to the heterogeneity of target organs innervated by these cells.

Postnatal synaptic development of the rat

Presynaptic boutons of the dorsomedial region of the nucleus tractus solitarius (NTS) were studied during the first 30 days of postnatal development of the rat. Electron micrographs were analyzed by conventional and stereological techniques to determine the area and volumetric density and fraction, and the number per linear length on both the dendrites and cell bodies. The numerical density and volumetric fraction of boutons in the NTS increased rapidly within the first 10 postnatal days. The number of boutons per area and volume remained stable between 10 and 30 days. Twice as many boutons synapsed on the larger dendrites than the cell bodies during the first 10 days, and then increased to 4 times the number of synapses per linear length on the cell body after the tenth postnatal day. The rapid synaptic development and shift in shift in sites of synaptic contact on neurons of the NTS suggest synaptic contacts rapidly change during early postnatal development.

Axonal trajectories of masticatory motoneurons: a genu formation of axons of jaw-opening motoneurons in the cat

Axonal courses of jaw-opening motoneurons were examined in the cat by applying horseradish peroxidase to the central cut end of the nerve branch which supplies the mylohyoid and/or the anterior digastric muscle. The axons of mylohyoid and anterior digastric motoneurons, which are located in the ventromedial division of the trigeminal motor nucleus, initially swing dorsally before running ventrolaterally to leave the pons; axons proceeding in the more rostral levels make turns in the more dorsomedial tegmental regions, and those running in the most rostral levels form a small genu in the region near the midline under the floor of the fourth ventricle.

Anatomical localization of the cells of origin of efferent fibers in the superior laryngeal and recurrent laryngeal nerves of dogs

Using horseradish peroxidase, we identified the cells of origin of motor fibers in the superior laryngeal and recurrent laryngeal nerves of dogs. Cells giving rise to fibers in the superior laryngeal nerve were found in the dorsal motor nucleus and the nucleus ambiguus, whereas cells giving rise to fibers in the recurrent laryngeal nerve were found in the nucleus ambiguus and nucleus retroambigualis, but usually not in the dorsal motor nucleus.

Central connections of the hepatic branch of the vagus nerve: a horseradish peroxidase histochemical study

The hepatic branch of the vagus nerve has been implicated as an important source of afferent input controlling both physiological and behavioral homeostasis. In addition, it is clear that parasympathetic efferents to the liver can significantly alter hepatic functions. In order to begin physiological studies on the nature of hepatic afferent and efferent relations, it will be necessary to understand the central anatomical organization of the components of this small visceral nerve. By carefully exposing and dissecting the hepatic branch of the vagus and applying crystalline horseradish peroxidase (HRP) to it, we were able to elucidate a predominant pattern of afferent terminations within the left subnucleus gelatinosus, the medial division of the left solitary nucleus and the left lateral edge of the area postrema. Efferent nuclei were concentrated in the left dorsal motor nucleus of the vagus (DMN) with a few scattered neurons located in the right DMN as well as the left anterior nucleus ambiguous.

Insula of the old world monkey. III: Efferent cortical output and comments on function

The insula sends neural efferents to cortical areas from which it receives reciprocal afferent projections. A collective consideration of afferents and efferents indicates that the insula has connections with principal sensory areas in the olfactory, gustatory, somesthetic (SI and SII), and auditory (AI and AII) modalities. There are additional connections with association areas for the visual (TEm), auditory (supratemporal plane), and somesthetic (posterior parietal cortex) modalities; with paramotor cortex (area 6 and perhaps MII); with polymodal association cortex; and with a wide range of paralimbic areas in the orbital, temporopolar, and cingulate areas. The topographic distribution of these connections suggests that the posterodorsal insula is specialized for auditory-somesthetic-skeletomotor function whereas the anteroventral insula is related to olfactory-gustatory-autonomic function. Most of the insula, especially its anteroventral portions, have extensive interconnections with limbic structures. Through its connections with the amygdala, the insula provides a pathway for somatosensory, auditory, gustatory, olfactory, and visceral sensations to reach the limbic system. The cortical areas connected with the granular sector of the insula are also granular in architecture whereas virtually all the connections of the agranular insula arise from allocortical, agranular, or dysgranular areas. Thus, there is a correspondence between the architecture of insular sectors and the areas with which they have connections. The insula is heavily interconnected with temporopolar and lateral orbital areas. Furthermore, many cortical connections of the lateral orbital cortex are quite similar to those of the insula. These common connectivity patterns support the conclusion, based on architectonic observations, that the insulo-orbito-temporopolar component of the paralimbic brain should be considered as an integrated unit of cerebral organization.

Area postrema lesions produce feeding deficits in the rat: effects of preoperative dieting and 2-deoxy-D-glucose

To investigate the possible role of the area postrema (AP) in the control of food intake and body weight, male albino rats were divided into four groups: (a) animals dieted to 80% of their original body weights prior to receiving AP lesions, (b) nondieted animals with AP lesions, (c) animals dieted to 80% prior to receiving sham lesions, and (d) nondieted animals with sham lesions. Lesions of the AP in nondieted rats resulted in hypophagia, hypodipsia and body weight loss followed by recovery of normal intake and maintenance of body weight at a fixed percentage of the sham operated animals' weight. Reducing body weight prior to surgery led to body weight maintenance levels equivalent to those of the nondieted groups. We also tested the animals for sensitivity to glucoprivation caused by intraperitoneal injections of 2-deoxy-D-glucose (2-DG). Injections of 2-DG produced hyperphagia in sham lesioned rats, but not in rats with AP lesions. Our data suggest that the effects of AP lesions on intake and body weight are similar, in several important respects, to the lateral hypothalamic feeding syndrome and to the effects of subdiaphragmatic vagotomy. We discuss the results with respect to hierarchical levels of neural circuitry involved in controlling feeding behavior.

The central projections of the trigeminal, facial, glossopharyngeal and vagus nerves: an autoradiographic study in the rat

The central distributions of primary afferent axons in the facial, trigeminal (mandibular branch), glossopharyngeal, and vagal nerves of the rat have been re-examined using the autoradiographic tracing technique after injections of [3H]proline or [3H]leucine into their peripheral ganglia. Within the nucleus of the solitary tract (NST), the labeled terminals from VII, V, IX and X form a continuous distribution that spans the length of this nucleus. Sensory axons in VII terminate mainly within the lateral division of the rostral NST, although some of the terminals extend further caudally within the nucleus. Immediately caudal to the rostral NST, the distribution continues with major contributions from V and IX. Both are confined mainly to the lateral division of the NST, although some of the fibers in IX terminate within the medial division. Injections into the inferior ganglion of X confirm the extensive distribution of vagal axons as they ramify significantly within the lateral division, and virtually monopolize the medial division of the NST. Thus, the major zone of convergency for these 4 cranial nerves is the lateral division of the nucleus from the level of the entering fascicles of IX caudally to the level of the area postrema. Furthermore, only X has a crossed projection as vagal axons invade the commissural nucleus and the medial division of the contralateral NST. Vagal fibers also enter the area postrema bilaterally. Finally, some afferent fibers from VII, IX and X descend in the dorsal part of the spinal trigeminal tract and terminate within the marginal subdivision of the spinal trigeminal nucleus pars caudalis, as well as the dorsal horn of the cervical spinal cord.

Brainstem projections of sensory and motor components of the vagus nerve in the rat

The sensory and motor connections of the cervical vagus nerves and of its inferior ganglion (nodose ganglion) have been traced in the medulla and upper cervical spinal cord of 16 male Wistar rats by using horseradish peroxidase (HRP) neurohistochemistry. The use of tetramethyl benzidine (TMB) as the substrate for HRP permitted the visualization of transganglionic and retrograde transport in sensory nerve terminals and perikarya, respectively. The vagus nerve in the rat enters the medulla in numerous fascicles with points of entry covering the entire lateral aspect of the medulla extending from level +4 to -6 mm rostrocaudal to the obex. Fascicles of vagal sensory fibers enter the dorsolateral aspect of the medulla and travel to the tractus solitarius (TS) which was labeled for over 8.8 mm in the medulla. The caudal extent of the TS receiving vagal projections was found in lamina V of the cervical spinal cord (C1 to C2). Sensory terminal fields could be visualized bilaterally in the nucleus of the tractus solitarius (nTS), area postrema (ap) and dorsal motor nucleus of the vagus nerve (dmnX). The ipsilateral projection to the nTS and the dmnX was heavier than that found on the contralateral side. The area postrema was intensely labeled on both sides. Motor fibers from HRP-labeled perikarya in the dmnX travel ventromedially in a distinct fascicle and subsequently subdivide into a number of small fiber bundles that traverse the medullary reticular formation in the form of a fine network of HRP-labeled fibers. As these fibers from the dmnX approach the ventrolateral aspect of the medulla they are joined by axons from the nucleus ambiguus (nA), nucleus retroambigualis (nRA) and the retrofacial nucleus (nRF). These latter fibers form hairpin loops in the middle of the reticular formation to accompany the axons from the dmnX exiting from the medulla in a ventrolateral location. HRP-labeled perikarya, in contrast to transganglionically transported HRP in sensory terminals in the nTS, were visualized on one side only, thus indicating that motor control via the vagus nerve is exerted only by motor neurons located ipsilaterally. Sensory information on the other hand, diverges to many nuclear subgroups located on both sides of the medulla.

Hexamethonium-resistant gastric contractions by stimulation of the vagal nuclei. An antidromic activation of vagal afferents?

Experiments were performed in chloralosed cats, laparotomized with ligated adrenals and spinalized in the cervical region. Blood pressure, heart rate and gastric motility were monitored. Stimulations were performed in two brain stem regions, viz. a "control region" including the nucleus ambiguous and a "dorsal region" approximately corresponding to the dorsal vagal nucleus and the solitarius complex. From both regions were regularly elicited gastric motor responses that were either excitatory, biphasic or inhibitory in direction, and always associated with prompt bradycardia and hypotension. After hexamethonium blockade of the "conventional" efferent vagal excitatory and relaxatory fibres to the stomach, stimulation of the control region no longer augmented gastric motility, while gastric contractions which could be abolished by atropine or vagotomy were produced from the dorsal region. The bradycardia and hypotension responses from both regions were also blocked by hexamethonium and then stimulations often led to delayed pressor responses, resistant to both vagotomy and atropine. The present results, together with previous findings (Delbro et al. 1981, 1982) suggest that the hexamethonium-resistant gastric contractions, elicited by stimulation of the mentioned dorsal region of the brain stem, are due to antidromic activation of afferent gastric vagal fibres with excitatory collaterals to intramural cholinergic neurons.

Sites of origin and termination of gastric vagus preganglionic neurons: an HRP study in the rat

Using the horseradish peroxidase (HRP) method, we studied the relation between sites and forms of gastric vagus preganglionic neurons in the rat and gastric regions on which they project. Fifty microliters of a physiological saline solution containing 3 mg of HRP was injected into 6 different gastric regions: cardia, lesser curvature, pyloric antrum, greatger curvature, ventral corpus and dorsal corpus. After a survival period of 24h, the medulla oblongata was serially sectioned and processed for histochemical demonstration of HRP. In the medulla oblongata, HRP-labeled cells were distributed in 2 regions: (1) in the regions within the dorsal vagus nucleus (DVN); (2) in the regions within the ambiguous complex. The labeled cells in the DVN were observed in every experiment, while ones in the ambiguous complex were only seen in the cardia and lesser curvature experiments. In the ventral corpus experiment the labeled cells were observed dominantly on the left side and in the dorsal corpus experiment dominantly on the right side. The majority of the labeled cells in the ambiguous complex were medium-sized and multipolar in shape, while the majority of ones in the DVN were medium-sized and fusiform in shape.

A study of the extrinsic innervation of the guinea pig pylorus with the horseradish peroxidase tracing technique

The extrinsic innervation of the guinea pig pylorus was studied by the use of the horseradish peroxidase (HRP) tracing technique. Forty-eight hours after injection of HRP into the pyloric sphincter labeled neurons of varying sizes were found throughout the rostrocaudal extent of the dorsal motor nuclei of the vagus. No HRP positive cells were seen in the medial solitary nuclei or the ambiguous nuclei. Many HRP-positive cells were observed in the celiac-superior mesenteric ganglion complex. Occasional cells in the superior cervical and stellate ganglia were also labeled. When the vagal ganglia were analyzed many enzyme-containing cells were found in the nodose ganglia and some cells in the jugular ganglia. Furthermore, about 15-20% of the labeled afferent neurons were located in dorsal root ganglia on both sides, with the majority of cells at the T5--T10 levels. The results are discussed in relation to recent transmitter histochemical findings as well as possible functional roles of the neurons.

Selective retrograde transport of 3H-serotonin in vagal afferents

A new serotonergic afferent vagal component has been demonstrated in the cat by radioautography. Twenty-four hours after a bilateral injection of tritiated serotonin (3H-5-HT) into the area of the nucleus of the solitary tract (NST), heavily and lightly labelled cell bodies were observed in the nodose ganglia. After unilateral injections of 3H-5-HT into the same area, labelled ganglionar cell bodies were found in the ipsilateral nodose ganglion. Some were also found in the contralateral one, suggesting a serotonergic crossed fibers component. Dense clusters of silver grains, depicting typical labelling of neuronal varicosities, were observed in the NST. After destruction of the serotonergic terminals with 5,7-dihydroxytryptamine, followed by injection of 3H-5-HT, the number of labelled cell bodies decreased dramatically in the ipsilateral nodose ganglia and the clusters of silver grains disappeared in the NST. After ligature or section of the supranodose vagal nerve, following injection of 3H-5-HT into the NST, no radioautographic reaction was observed in the homolateral nodose ganglia. The present study demonstrates the existence of a peripheral serotonergic system in vagal afferents. The physiological implications of this new serotonergic visceral pathway remain to be studied.

Ultrastructural evidence in mice that transganglionically transported horseradish peroxidase-wheat germ agglutinin conjugate reaches the intraspinal terminations of sensory neurons

Horseradish peroxidase conjugated to wheat germ agglutinin (HRP-WGA) has been localized by electron microscopy in the central projections of primary sensory neurons following injection of the tracer into the gastrocnemius muscle of mice. The tracer was taken up by nerve terminals in the muscle and transported transganglionically into the central spinal cord terminations of the primary sensory neurons. The HRP-WGA was localized using a new tetramethylbenzidine ultracytochemical method and the diaminobenzidine-glucose oxidase technique. The results demonstrate that the HRP-WGA is transported into the axon terminals after passing through the sensory ganglion. These data provide an experimental basis for the use of the conjugate to map the central projections of sensory neurons.

Medullary cells of origin of physiologically identified cardiac nerves in the dog

Individual cardiac nerves from which stimulation elicited cardioinhibition (bradycardia and negative inotropism) were identified in 24 of 38 dogs. Subsequently, 3-25 microliters of 30% horseradish peroxidase (HRP) were injected into an identified cardiac nerve. After a 3-day survival period, the medulla oblongata was processed for HRP histochemistry. Retrograde labeling was observed to be concentrated primarily in the ipsilateral nucleus ambiguus (NA) and in medium-sized neurons located ventral and lateral to the larger neurons of the principal NA cell column. This latter location was so characteristic that it has been designated the ventrolateral nucleus ambiguus (VLNA). Labeled neurons were found at all levels of the NA and VLNA and their distribution was similar irrespective of the cardiac nerve injected. Relatively few labeled neurons were observed in the dorsal motor nucleus of the vagus nerve (DMV) except after injections into the left and right recurrent cardiac nerves and the left cranial vagal nerve. In some dogs labeled cells were present only in and ventrolateral to the NA and not in the DMV, even though stimulation of the injected nerve elicited both bradycardia and negative inotropism. These results demonstrate that ventrolateral regions of the NA represent the major site of cardioinhibitory motor neurons in the dog that they can regulate both rate and force.

The ultrastructure of the subnucleus gelatinosus of the nucleus of the tractus solitarius in the cat

The dorsomedial region of the nucleus of the tractus solitarius termed the subnucleus gelatinosus (SNG) was studied at the light and electron microscopic level in the cat. In cresyl violet and luxol fast blue stained sections the SNG contained small neuronal somata that were scattered throughout a pale-staining neuropil containing few myelinated fibers. These neurons were difficult to impregnate with Golgi staining techniques, but in successful impregnations the somata were observed to be 10--19 micrometers in diameter and bore few sparsely branching primary dendrites. Spines were present on the dendrites of some neurons and were more numerous on distal portions of the dendritic tree. Ultrastructural examination of the SNG revealed that the neuronal complement consisted of round, oval, or spindle shaped neurons with little or no organized Nissl substance. Rare myelin-like ensheathments of neuronal perikarya were also observed. Bundles of fine unmyelinated axons that coursed mainly longitudinally were a prominent feature of the area. The most common type of axon terminal observed contained mainly round clear vesicles, approximately 31 nm in diameter, and made asymmetrical synaptic contact with a dendritic profile. Pleomorphic vesicle-containing terminals involved in symmetrical synaptic contact were also commonly seen. Axodendritic and axosomatic synapses were associated with terminals containing either round clear vesicles or pleomorphic vesicles. Less commonly, dendrodendritic and dendrosomatic synapses were seen, the presynaptic elements of which contained pleomorphic vesicles. Following removal of a nodose ganglion, degenerating terminals of vagal afferent fibers were observed throughout the neuropil. Such terminals contained round, clear vesicles with an occasional large, dense-cored vesicle, and made axodendritic and axosomatic synaptic contacts.

Origins of cardiac vagal preganglionic fibers: a retrograde transport study

The origin of cardiac preganglionic neurons in the rat was investigated using the retrograde transport of horseradish peroxidase (HRP). A single injection of HRP was made into the right myocardium in either a sinoatrial or mid-ventricular location. Labeled cells were found in the mid- and lower medulla primarily in and around the nucleus ambiguous (NA) 600-1800 micrometers above the obex. The dorsal motor nucleus of X (DMN) was sparsely labeled and a few cells were found in an intermediate zone near the level of the obex. Labeling was bilateral with slightly heavier labeling found ipsilateral to the injection site than contralateral to it. Following a unilateral vagotomy, labeled cells were only found ipsilateral to the intact vagus. Atrial and midventricular injections yielded similar results. Occasionally only 1-2 cells in the NA were labeled per section. Inspection of serial sections revealed that in these sparsely labeled rats, the HRP was often in the same location within the NA forming a column of cells within the nucleus. The columns sometimes extended at least 240 micrometers in the rostral-caudal direction. The columnar organization was most apparent in rats with few labeled cells presumably because it was obscured in nuclei that were heavily labeled. In a second group of rats, the right vagus was cut at the cervical level and dipped in HRP to determine the extent of the NA and DMN in rats. In these animals, heavier labeling was found in the DMN than in the NA. Cells in the DMN were filled from the upper spinal cord to its most rostral extent 1200 micrometers above the obex. Thus, although the DMN and NA send projections in the vagus nerve, those axons terminating in the myocardium primarily originate in the NA.

The brain-stem projections of pulmonary stretch afferent neurones in cats and rabbits

1. Micro-electrode recordings were made from slowly adapting pulmonary stretch afferents within the nodose ganglia of cats and rabbits. Recordings sites were distributed throughout the ganglia. 2. The projections of these afferents to the medulla oblongata were studied by antidromic stimulation. 'Point' and 'Field' type depth--threshold curves were interpreted as corresponding to stimulation of the main afferent axons and its branches, respectively. Increases in antidromic latency in conjunction with 'field' contours was additional evidence in support of this interpretation. 3. In cats, most (six out of seven) afferents had extensive branches, and probably also terminations, within the medial subnucleus of the ipsilateral nucleus tractus solitarius (n.t.s.). Two of these, plus one other afferent, also had projections to the lateral and ventrolateral subnuclei. 4. In rabbits the projections of such afferents were similar, i.e. mainly to the medial subnucleus of the n.t.s. (eight out of eleven) but also extending into the nucleus alaris, and occasionally to lateral and ventrolateral subnuclei (two out of eleven) or to both regions (one out of eleven). 5. Branching of single afferents was seen to occur over up to 3 mm of the rostro-caudal extent of the intermediate region of the n.t.s. The significance of the observations is discussed.

Medullary origin of vagal preganglionic axons to the heart of the cat

It is apparent from the literature that a controversy exists concerning the site of origin of cardiac vagal preganglionic axons. Physiological studies have suggested that the location of these neurons may be different in different species and there has been disagreement between physiological and anatomical findings in the same species. We now present anatomical and neurophysiological studies suggesting that in the cat cardiac vagal preganglionic neurons are located in two medullary regions: the areas of the dorsal motor nucleus of the vagus (DMV) and of the nucleus ambiguus (AMB). This suggestion is based on the following observations. Firstly, after application of horseradish peroxidase to the right cardiac branches of the vagus nerve, labeled neurons were found primarily in the regions of te DMV and AMB. Additional scattered neurons were found in the reticular formation between these two nuclei. Secondly, following injections of tritiated amino acids into either the DMV or AMB, labeled vagal fibers were found in the atrial myocardium. Finally, electrical stimulation of the right cardiac branches of the vagus nerve antidromically activated DMV or AMB, labeled vagal fibers were found in the atrial myocardium. Finally, neurons in the DMV and AMB regions with latencies corresponding to conduction velocities of B-fibers. In addition, these neurons were orthodromically excited by electrical stimulation of the carotid sinus and aortic depressor nerves.

Identification and localization of the motor nuclei and sensory projections of the glossopharyngeal, vagus, and hypoglossal nerves of the cockatoo (Cacatua roseicapilla), Cacatuidae

Horseradish peroxidase (HRP) has been applied to the proximal severed ends of glossopharyngeal (N IX), vagus (NX), and hypoglossal (N XII) cockatoo in order to localize the motoneurons and sensory projections of these nerves which are involved in the control of the bird's feeding and phonatory behaviors. Application of HRP to N IX labeled four rhombencephalic nuclei: (1) a large-celled, retrofacial nucleus supplying M. geniohyoideus, the major tongue extensor; (2) a dorsal nucleus composed of medium-sized cells, projecting to most branches of N IX; (3) a ventrolateral nucleus supplying, amongst other structures, the floor of the pharynx and larynx; and (4) a ventral portion of the dorsal motor nucleus of the vagus. Neurons labeled by application of HRP to the cervical vagus comprise the classically defined dorsal motor nucleus and a ventrolateral medullary nucleus which is coextensive with that of the glossopharyngeus: together they probably constitute a nucleus ambiguus. Application of HRP to hypoglossal branches labeled a large nucleus intermedius (IM) and neurons ventral, ventrolateral, and caudal to it. The rostral third of IM supplies the lingual muscles, the caudal two-thirds the tracheosyringeal muscles. Many labeled neurons were found in the "jugular" ganglion following HRP treatment of each of the three nerves, especially N IX and N XII, which innervate the tongue. Central projections of these neurons are to nuclei of the descending trigeminus and to largely nonoverlapping portions of the principal trigeminal nucleus. It is hypothesized that these afferents provide sensory information necessary for the efficient processing and passage of food in the mouth.

Localization of sympathetic postganglionic neurons of physiologically identified cardiac nerves in the dog

Cardiac nerves were identified physiologically and injected with horseradish peroxidase in 38 dogs. Retrogradely labeled neurons were present in the greatest number in the middle cervical ganglion, whereas fewer labeled neurons were present in the stellate ganglion. Only occasional neurons in the superior cervical ganglion were labeled, and no labelphysiologically and injected with horseradish peroxidase in 38 dogs. Retrogradely labeled neurons were present in the greatest number in the middle cervical ganglion, whereas fewer labeled neurons were present in the stellate ganglion. Only occasional neurons in the superior cervical ganglion were labeled, and no labelphysiologically and injected with horseradish peroxidase in 38 dogs. Retrogradely labeled neurons were present in the greatest number in the middle cervical ganglion, whereas fewer labeled neurons were present in the stellate ganglion. Only occasional neurons in the superior cervical ganglion were labeled, and no labeled cells were found in the T3 to T6 paravertebral ganglia or in the ganglia contralateral to the nerve injected. following injections into specific cardiac nerves, retrograde labeling was widespread within the middle cervical ganglion, and the distributions of labeled neurons from different nerves overlapped considerably. In the middle cervical ganglion there was little or no regional grouping of cells projecting to specific cardiac nerves. within the stellate ganglion, however, te cardiac-sympathetic cells were clustered primarily at the cranial pole near toe origin of the ventral and dorsal ansae. Mediastinal ganglia and ganglia located in cardiac nerves were frequently as heavily labeled as the ipsilateral stellate ganglion. The occurrence of heavy labeling in mediastinal and cardiac nerve ganglia indicates that these hitherto unreported ganglia play a significant role in cardiac neural regulation. These data imply that the organization of sympathetic neurons controlling the heart is much more complex than has previously been considered.

Hindbrain GABA receptors influence parasympathetic outflow to the stomach

Blockade of gamma-aminobutyric acid receptor function by direct microinjection of bicuculline into the nucleus ambiguous in cats produced a marked increase in gastric motility which was mediated by the vagus nerve. This effect was reversed by muscimol. These data indicate that the nucleus ambiguous may be an important brain site influencing gastric function and that the neurotransmitter controlling parasympathetic overflow from this nucleus to the stomach is gamma-aminobutyric acid.

Innervation of the thymus gland by brain stem and spinal cord in mouse and rat

Central nervous system (CNS) projections to the thymus were studied in the mouse and rat using the horseradish peroxidase (HRP)-retrograde transport method. With discrete HRP injections localized to the thymus, labeled neurons are evident in both medulla and spinal cord. In the medulla the largest population of labeled neurons is present in the retrofacial nucleus. Within this cytoarchitectonically distinct nucleus, the majority of neurons are labeled with large HRP injections in the thymus. In addition to retrofacial nucleus, scattered labeled neurons are found throughout the rostrocaudal extent of the nucleus ambiguus and in the dorsal medullary tegmentum adjacent to the dorsal motor vagus nucleus. With HRP injections restricted to thymus parenchyma, no labeled neurons are evident in the dorsal motor vagus nucleus. Three groups of spinal cord neurons are labeled. In segments C2-C4, neurons localized to the ventral horn are labeled in two distinct columns, one located lying laterally in the ventral horn and the other located medially. Labeling of neurons in these segments is distinct from that of large motor neurons located medially in the ventral horn extending from the level of the decussation of the pyramids through the C1 segment. The location and sizes of neurons labeled in these areas following HRP injection in the thymus are identical in the mouse and rat. These observations provide evidence for previously unknown projections from spinal cord and brain stem to the thymus which may play an important role in the regulation of thymic function.

Baroreflex actions of substance P microinjected into the nucleus tractus solitarii in rat: a consequence of local distortion

Biologically active substance P (SP) (1000 ng in 0.1 microliter saline) microinjected into the nucleus tractus solitarii (NTS) of 25 rats did not affect arterial pressure, heart rate, or the baroreceptor reflex. However, microinjection of saline alone in volumes greater than 0.3 microliter consistently elicited hypotension and bradycardia followed occasionally by transient hypertension. These data suggest that previously reported cardiovascular effects of SP microinjected into the NTS resulted from local distortion.

Evidence for the site of the superior salivatory nucleus in the guinea pig: a retrograde HRP study

Horseradish peroxidase (HRP) was applied to the proximal end of the severed lingual nerve distal to where it was joined by the chorda tympani nerve in 15 female guinea pigs. Labeled cells were seen in the lateral reticular formation dorsal to the facial nucleus along the medial edge of the spinal nucleus of V. These cells were aligned vertically and partially within the facial nerve fibers which were emerging from the facial nucleus lying ventrally. HRP-reactive axons were also seen among the facial nerve fibers coursing dorsomedially toward the genu of the facial nerve. These results demonstrated for the first time the locus of the superior salivatory nucleus in the guinea pig and were consistent with anatomical results previously reported in other species. In addition, labeled fibers indicated that superior salivatory nucleus axons became incorporated in the facial nerve immediately dorsal to its origin.

Antagonism of the baroreceptor reflex by glutamate diethyl ester, an antagonist to L-glutamate

Recent reports have suggested that the excitatory amino acid L-glutamate is a neurotransmitter released by baroreceptor afferent nerves at their termination in the nucleus tractus solitarii (NTS). In this study we have examined the effect on arterial pressure, heart rate and baroreflex activity of the glutamate antagonist glutamate diethyl ester (GDEE) microinjected into the NTS of 50 rats anesthetized with Chloralose. Bilateral injections of GDEE produced dose dependent transient hypertension. The threshold dose was 2.5 micrograms/NTS and at a dose of 15 micrograms/NTS a maximal rise in arterial pressure and heart rate (from 95 +/- 8.7 mm Hg to 153 +/- 6.4 mm Hg and from 322 +/- 14.7 beats/min to 364 +/- 16.2 beats/min respectively, P less than 0.001, n = 6) occurred. A dose of 15 micrograms/NTS also completely blocked the baroreflex when injections were made bilaterally and it totally antagonized the cardiovascular effects of L-glutamate when injected immediately prior to L-glutamate. The hypertension, the antagonism of L-glutamate, and the blockade of the baroreflex persisted for 20-30 min. In that L-glutamate mediates a baroreflex-like response upon injection into NTS and in that GDEE blocks that response while at the same time blocking the naturally occurring baroreflex, the data are consistent with L-glutamate being a neurotransmitter of baroreflex afferents.

Carotid sinus nerve projections to the brain stem in the cat

The distribution of carotid sinus nerve (CNS) afferent and efferent fibers in the brain stem was examined in eight cats using horseradish peroxidase (HRP) neurohistochemistry. The transganglionic transport of HRP yielded dense extraperikaryal labeling within the nucleus of the tractus solitarius (nTS). Labeling was also present in the area postrema (ap) and in the region of the nucleus ambiguus (nA). The nTS labeling was bilateral, the ipsilateral side being more intense. Within the nTS, the labeling was not uniform, being heaviest in the dorsal, dorsolateral and commissural subnuclei. Moderate labeling was seen in the ventrolateral nTS. In the region of the obex, HRP labeled fibers could be followed from the nTS to the region of the nA, where extraperikaryal labeling could be seen. HRP labeled perikarya were found in the rostral pole of nA. In two controls, the CSN was sectioned close to its junction to the glossopharyngeal nerve just prior to HRP injection. In both cases, no labeling was found in either the petrosal ganglion or brain stem.

Brain stem localization of vagal preganglionic neurons

The central distribution of vagal preganglionic neurons has been examined using the retrograde transport of horseradish peroxidase (HRP). In 27 adult cats, the entire vagus nerve was exposed to HRP. In 13 other cats we examined the brain stem following microinjections of HRP (10 microliter) into individual visceral organs - lung, heart and stomach. Comparison of individual cases led to the conclusion that different patterns exist for each visceral organ. The preganglionic (parasympathetic) innervation of the entire vagus nerve arises from the dorsal motor nucleus of the vagus (dmnX), nucleus ambiguus (nA), nucleus retroambigualis (nRA), nucleus dorso-medialis (ndm), spinal nucleus of the accessory (nspA) and from the reticular formation between the dmnX and nA. Axons arising from the nA do not traverse the medulla laterally; rather they are initially directed dorso-medially toward the dmnX where they bend at right angles and accompany axons of neurons in the dmnX. The motor nuclei innervating the lungs, heart and stomach are dmnX, the nA and nRA: the dmnX contributes fibers to the heart, lungs and stomach from a region of 10 mm of medulla rostrocaudally; the nA contributes efferents to the 3 viscera studied from the entire 6 mm contributing vagal efferents; the nRA contributes efferents to the stomach in addition to providing innervation to the larynx and trachea (see 19). The area postrema (ap) receives afferent input from the lungs, heart and stomach, as indicated by extraperikaryal grains of HRP reaction product resulting from transganglionically transported HRP (through the ganglion nodosum). Sensory terminal labeling in the various subnuclei of the nucleus of the tractus solitarius (nTS) was also examined and it was found that no specific region of the medulla is devoted to receiving input from any one visceral organ; rather the rostro-caudal extent of vagal afferent terminals in the medulla spans the entire length of the medulla. Differences between the central representation of different viscera seemed to lie within the organization of the nuclear subgroups of the nTS.