Bombesin immunoreactive neurons in the hypothalamic paraventricular nucleus innervate the dorsal vagal complex in the rat

Bombesin-like immunoreactivity has been localized within neuronal cell bodies of the hypothalamus and nerve terminals within the dorsal vagal complex. The possibility that the hypothalamus is a source for bombesin-like immunoreactive terminals within the dorsal vagal complex was examined using the combined retrograde tracing and immunohistochemical technique. After injections of retrograde tracer were made into the dorsal vagal complex, cells in the hypothalamus labeled with both retrograde tracer and bombesin immunoreactivity were localized in the parvocellular part of the paraventricular nucleus. In the paraventricular nucleus most of the vagal projecting bombesin immunoreactive neurons were located within the medial parvocellular subdivision. Approximately 30% of the bombesin immunoreactive neurons in this subnucleus projected to the dorsal vagal complex. The results suggest that the paraventricular hypothalamic nucleus is a major source of bombesin terminals within the dorsal vagal complex. This pathway may mediate some of the autonomic nervous system changes that are observed when bombesin is injected within the central nervous system. Additionally, this data adds to a growing amount of evidence supporting the role of bombesin as a peptide neurotransmitter.     

Olanzapine treatment decreases the density of muscarinic M2 receptors in the dorsal vagal complex of rats

In this study, we investigated the effects of antipsychotic drugs, olanzapine and haloperidol, on the density of the muscarinic M2 receptors in the dorsal vagal complex (DVC) and hypoglossal nucleus (HN). Female Sprague Dawley rats were treated with olanzapine, haloperidol or vehicle (control) for 1 (short-term) or 12 weeks (long-term). Quantitative autoradiography was used to investigate the M2 receptor density in the DVC and HN using a muscarinic antagonist [(3)H] AF-DX384. Olanzapine, but not haloperidol, treatment induced a significant decrease in the binding density of M2 receptors in the DVC compared to control groups. Although the HN showed a higher density of [(3)H] AF-DX384 binding than the DVC, treatment with both olanzapine and haloperidol did not induce any significant changes in [(3)H] AF-DX384 binding in the HN. These results suggest that olanzapine-induced body weight gain may be associated with functional changes in the muscarinic neurotransmission in the DVC.     

Projections of the lateral hypothalamus and bed nucleus of the stria terminalis to the dorsal vagal complex in the pigeon

The dorsal vagal complex is composed of the nucleus tractus solitarii (Nts) and the dorsal motor nucleus of the vagus (DMN X). In the pigeon, these nuclei are composed of cytoarchitectonically well-defined subnuclear groups, which have connections that are partially segregated to specific organs (Katz and Karten: J. Comp. Neurol. 218:42-73, '83b, J. Comp. Neurol. 242:397-414, '85). The present study sought to determine whether forebrain afferents to Nts-DMN X are differentially distributed to specific subnuclei and thereby modulate the functions of specific organs. Forebrain afferents to the dorsal vagal complex were determined by retrograde tracing techniques. Labeled perikarya were found in the bed nucleus of the stria terminalis (BNST), ventral paleostriatum, and stratum cellulare externum (SCE) of the lateral hypothalamus, and in the medial hypothalamus, nucleus periventricularis magnocellularis (PVM), which is the avian homologue to a portion of the mammalian paraventricular nucleus. The pattern of axonal distribution to Nts-DMN X subnuclei from the BNST-ventral paleostriatum and SCE were investigated by anterograde tracing techniques. These experiments revealed axonal projections distributed to specific Nts-DMN X subnuclei. However, there is a high degree of overlap of the axonal projections to Nts-DMN X subnuclei from BNST-ventral paleostriatum and SCE, as well as from PVM (Berk and Finkelstein: J. Comp. Neurol. 220:127-136, '83). Labeled fibers from BNST-ventral paleostriatum and SCE project heavily to Nts subnuclei medialis superficialis, lateralis dorsalis, and medialis ventralis and to DMN X subnucleus ventralis parvicellularis. Fewer labeled fibers were found in Nts subnucleus medialis intermedius and extremely sparse labeling was found in Nts subnucleus medialis dorsalis. The Nts and DMN X subnuclei that receive forebrain projections also have peripheral connections with the aortic nerve, crop, esophagus, glandular stomach, and caudal abdominal organs. Thus, the forebrain could modulate the functions of these segments of the cardiovascular and digestive systems.     

The ultrastructural localization of enkephalin and substance P immunoreactivities in the nucleus tractus solitarii of the cat

In the medial and commissural subdivisions of the nucleus tractus solitarii enkephalin and substance P immunoreactivities were localized within synaptic terminals, unmyelinated axons, and neuronal cell bodies. Both enkephalin and substance P immunoreactivities were contained within synaptic terminals which had a mixture of small clear vesicles and dense core vesicles. The presence of dense core vesicles within both the enkephalin- and substance P-immunoreactive terminals was a consistent feature, although they were not associated with the actual synaptic junction. While enkephalin- and substance P-immunoreactive terminals shared a similar morphology, their respective distributions along the dendritic tree were quite distinct. Enkephalin-immunoreactive terminals contacted mainly the cell body and proximal portions of the dendritic tree. In contrast, substance P-immunoreactive terminals synapsed predominantly with spines and shafts of small to medium-sized dendrites. Few substance P-immunoreactive terminals contacted proximal dendrites and they were never presynaptic to the neuronal cell body. This apparent segregation of synaptic terminals on neurons suggests that enkephalin synapses have a more pronounced effect than substance P terminals.     

Organization of serotonin 1A and 1B receptors in the nucleus of the solitary tract

We utilized 3H-8-hydroxy-N,N-dipropyl-2-aminotetralin (3H-DPAT) and 125I-iodocyanopindolol (125I-CYP) to label serotonin (5HT) 1A and 5HT1B receptors, respectively, in sections of the rat brain after characterizing the pharmacologic specificity of these agents. We then used quantitative autoradiography to measure the concentrations of 5HT1A and 5HT1B receptors in individual subnuclei of the nucleus of the solitary tract (NTS) and adjacent structures of the dorsal vagal complex. The highest 5HT1A receptor concentrations were observed within the central and intermediate subnuclei of the NTS, with low quantities of 3H-DPAT binding sites observed in the hypoglossal nucleus and dorsal motor nucleus of the vagus. In contrast, the density of 5HT1B receptors was relatively homogeneous through all NTS subnuclei, with the highest concentrations localized within the ventrolateral subnucleus. The hypoglossal and dorsal motor nuclei had slightly higher 5HT1B receptor densities than the NTS subnuclei, whereas the area postrema had a very low density. These data suggest that 5HT1A receptors are organized in a manner consistent with the cytoarchitectural and hodological parcellation of the NTS into individual subnuclei. The high concentrations of 5HT1A receptors in the central and intermediate subnuclei suggest a role for these receptors in medullary reflex pathways subserving deglutition. The relatively high density of 5HT1B receptors in the ventrolateral subnucleus suggests that these receptors modulate respiratory neurons, whereas the diffuse organization of 5HT1B receptors in the remaining subnuclei suggests that they are associated with central 5HT afferent pathways to the NTS. Further studies will be required to understand the physiologic role of 5HT1 receptors within the NTS.     

Thyrotropin-releasing hormone-immunoreactive nerve terminals synapse on the dendrites of gastric vagal motoneurons in the rat

Thyrotropin-releasing hormone stimulates vagally mediated gastric acid secretion and motility by an undefined central mechanism in the rat. The present study sought to determine the anatomical basis for this stimulatory effect by examining the ultrastructural relationship of nerve terminals immunoreactive for thyrotropin-releasing hormone with the dendrites of gastric vagal motoneurons. A light and electron microscopic double immunostaining technique was employed using the beta subunit of unconjugated cholera toxin as a neural tracer. Cholera toxin (50 microliters, 0.25%) was injected into the ventral stomach musculature in five rats. After 72 hours' survival, animals were sacrificed by transcardiac perfusion fixation. Retrogradely transported cholera toxin was immunocytochemically localized in vagal gastric motoneurons and their dendrites in the dorsal motor nucleus of the vagus and nucleus of the solitary tract, alone or in combination with the immunocytochemical localization of thyrotropin-releasing hormone. Ultrastructural analysis of double-labeled material revealed thyrotropin-releasing hormone-immunoreactive nerve terminals making asymmetric synaptic contacts on the retrogradely labeled dendrites of vagal gastric motoneurons. Nerve terminals immunoreactive for thyrotropin-releasing hormone also made asymmetric and symmetric synaptic contacts with unlabeled dendrites of undetermined perikaryal origin. In addition, nonsynaptic varicosities immunoreactive for thyrotropin-releasing hormone were frequently observed in the vagal nuclei. The synaptic contacts between thyrotropin-releasing hormone-immunoreactive nerve terminals and vagal gastric motoneuronal dendrites provide one possible basis for the profound stimulatory effect of central thyrotropin-releasing hormone on gastric vagal motor activity.     

Subregional topography of capillaries in the dorsal vagal complex of rats: I. Morphometric properties

Cytoarchitectonic and neurochemical studies of the dorsal vagal complex in the caudal medulla oblongata of rats indicate the existence of distinct anatomical and functional compartments within its components. We applied morphometric methods to discern whether capillary networks differed quantitatively between subregions and zones of area postrema, nucleus tractus solitarii (NTS), and dorsal motor nucleus of the vagus nerve (DMN) of rats. Analysis of 11 subdivisions of area postrema identified both "true" (range in luminal diameter of 3-7.5 microns) and sinusoidal (luminal diameter greater than 7.5 microns) capillaries that, together, made the capillary density for most of area postrema 75% greater than that found in NTS and DMN (526/mm2 vs about 300/mm2). The rank order of true capillary density in area postrema along its rostracaudal axis was caudal greater than central greater than rostral, whereas the reverse order was true for sinusoidal capillaries. Dorsal (periventricular) and medial zones of area postrema throughout its rostrocaudal axis tended to have higher values for capillary density, volume, surface area, luminal diameter, and pericapillary space volume than lateral or ventral zones bordering NTS. Within 200 microns of obex, the ventral zone of rostral area postrema was distinct, having a relatively sparse capillary density that may indicate morphological specializations limiting blood-tissue communication in this subregion. There were no quantitative differences in capillary dimensions between DMN and three subnuclei of NTS. These studies add to extant evidence that the dorsal vagal complex is differentiated for specific functions. Area postrema, especially, has topographical diversity in its capillary organization that likely corresponds to complex roles in neuroendocrine, autonomic, and chemosensory mechanisms.     

Autoradiographic localization of thyrotropin-releasing hormone receptors in the rat central nervous system

We employed quantitative autoradiography to examine the distribution of thyrotropin-releasing hormone (TRH) receptors in the rat CNS. The binding of [3H]3-methyl-histidine-TRH [( 3H]MeTRH) to TRH receptors in frozen rat brain sections was saturable, of a high affinity (Kd = 5 nM), and specific for TRH analogs. Autoradiograms of [3H]MeTRH binding showed highest concentrations of TRH receptors in the rhinencephalon, including accessory olfactory bulb, nuclei of the amygdala, and the ventral dentate gyrus and subiculum of the hippocampus. Moderate TRH receptor concentrations were found within the thalamus and hypothalamus, in most regions of the rhombencephalon, such as the cranial nerve nuclei, and in the substantia gelatinosa of the spinal cord. Neocortex and basal ganglia contained low densities of TRH receptors. This distribution correlates well with the sensitivity of brain regions to the known effects of TRH, and suggests that TRH receptors may mediate the actions of TRH in the rat CNS.     

Subregional topography of capillaries in the dorsal vagal complex of rats: II. Physiological properties

The differentiated cytoarchitecture, neurochemistry, and capillary organization of the rat dorsal vagal complex prompted this comprehensive investigation of microvascular physiology in 11 subdivisions of area postrema, 5 subnuclei of nucleus tractus solitarii (NTS), the dorsal motor nucleus of the vagus nerve, and 4 other gray matter structures in the dorsal medulla oblongata. Microvascular exchangeable volume (residual plasma volume), capillary blood and plasma flow, and unidirectional transfer constants for a tracer amino acid, [14C]alpha-aminoisobutyric acid (AIB), varied considerably among the structures analyzed. Exchangeable volume, largest in area postrema medial zones (about 29 microliters.g-1) and smallest in medullary gray matter (7-11 microliters.g-1), correlated directly with subregional densities of capillaries and rates of tissue glucose metabolism. Capillary blood flow (range of 1,430-2,147 microliters.g-1.min-1), plasma flow, and tissue glucose metabolism (range of 0.48-0.71 mumol.g-1.min-1) were linearly related in the dorsal vagal complex. The most striking quantitative difference among structures in this brain region were the rates of transcapillary influx and derived permeability X surface area (PS) products of [14C]AIB, which has physicochemical properties resembling those of hormones. PS products for AIB were negligible in most medullary gray matter regions (less than 1 microliter.g-1.min-1, indicative of blood-brain barrier properties), but were 20-59X and 99-402X higher in NTS subnuclei and area postrema, respectively. An extraordinary feature of the microcirculation in area postrema was the long-duration transit of tracer sucrose and blood, a characteristic that would amplify the sensing ability of area postrema as it monitors the composition of the circulation.     

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 μl 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 μl 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.     

Chemical coding and central projections of gastric vagal afferent neurons

Abstract  Vagal afferents that innervate gastric muscle or mucosa transmit distinct sensory information from their endings to the nucleus of the tractus solitarius (NTS). While these afferent subtypes are functionally distinct, no neurochemical correlate has been described and it is unknown whether they terminate in different central locations. This study aimed to identify gastric vagal afferent subtypes in the nodose ganglion (NG) of ferrets, their terminal areas in NTS and neurochemistry for isolectin-B4 (IB4) and calcitonin gene-related peptide (CGRP). Vagal afferents were traced from gastric muscle or mucosa and IB4 and CGRP labelling assessed in NG and NTS. 7 ± 1% and 6 ± 1% of NG neurons were traced from gastric muscle or mucosa respectively; these were more likely to label for CGRP or for both CGRP and IB4 than other NG neurons ( P  <   0.01). Muscular afferents were also less likely than others to label with IB4 ( P  <   0.001). Less than 1% of NG neurons were traced from both muscle and mucosa. Central terminals of both afferent subtypes occurred in the subnucleus gelatinosus of the NTS, but did not overlap completely. This region also labelled for CGRP and IB4. We conclude that while vagal afferents from gastric muscle and mucosa differ little in their chemical coding for CGRP and IB4, they can be traced selectively from their peripheral endings to NG and to overlapping and distinct regions of NTS. Thus, there is an anatomical substrate for convergent NTS integration for both types of afferent input.     

Oxytocin-immunoreactive innervation of identified neurons in the rat dorsal vagal complex

Background Oxytocin (OXT) has been implicated in reproduction and social interactions and in the control of digestion and blood pressure. OXT‐immunoreactive axons occur in the dorsal vagal complex (DVC; nucleus tractus solitarius, NTS, dorsal motor nucleus of the vagus, DMV, and area postrema, AP), which contains neurons that regulate autonomic homeostasis. The aim of the present work is to provide a systematic investigation of the OXT‐immunoreactive innervation of dorsal motor nucleus of the vagus (DMV) neurons involved in the control of gastrointestinal (GI) function. Methods We studied DMV neurons identified by (i) prior injection of retrograde tracers in the stomach, ileum, or cervical vagus or (ii) induction of c‐fos expression by glucoprivation with 2‐deoxyglucose. Another subgroup of DMV neurons was identified electrophysiologically by stimulation of the cervical vagus and then juxtacellularly labeled with biotinamide. We used two‐ or three‐color immunoperoxidase labeling for studies at the light microscopic level. Key Results Close appositions from OXT‐immunoreactive varicosities were found on the cell bodies, dendrites, and axons of DMV neurons that projected to the GI tract and that responded to 2‐deoxyglucose and juxtacellularly labeled DMV neurons. Double staining for OXT and choline acetyltransferase revealed that OXT innervation was heavier in the caudal and lateral DMV than in other regions. OXT‐immunoreactive varicosities also closely apposed a small subset of tyrosine hydroxylase‐immunoreactive NTS and DMV neurons. Conclusions & Inferences Our results provide the first anatomical evidence for direct OXT‐immunoreactive innervation of GI‐related neurons in the DMV.     

Distribution of neurotensin-immunoreactivity within baroreceptive portions of the nucleus of the tractus solitarius and the dorsal vagal nucleus of the rat

We have examined the distribution of neurotensin immunoreactivity within subnuclear regions of the nucleus of the tractus solitarius (NTS) and the dorsal motor nucleus of the vagus nerve (DVN) in the rat. In order to determine which regions of the NTS were involved in the regulation of baroreceptor reflexes, we mapped the central distribution of the aortic branch of the vagus nerve using transganglionic transport of horseradish peroxidase. Comparison of the pattern of aortic nerve innervation with that of the distribution of neurotensin-immunoreactive cells and fibers shows the dorsomedial nucleus of the NTS both to be the primary site of aortic baroreceptor termination and to contain the highest concentration of neurotensin-immunoreactive elements within the NTS. Neurotensin-immunoreactive fibers are also present in medial regions of the NTS adjacent to the area postrema where they may be involved in the modulation of vagal gastric afferents. Double-label experiments, in which, on the same tissue sections, neurotensin immunohistochemistry was combined with retrograde horseradish peroxidase labeling of DVN neurons, reveal a topographic innervation of vagal preganglionic motoneurons by neurotensin-immunoreactive fibers. The heaviest innervation is of lateral portions of the DVN and adjacent ventral portions of the NTS at the level of the obex, an area which may contain cardiac motoneurons. In this region neurotensin-immunoreactive fibers can be observed in close proximity to retrogradely labeled cells. The concentration of neurotensin elements in a region of the NTS which is involved in the control of baroreceptor reflexes provides a morphological basis for the cardiovascular effects produced by central administration of the peptide. Additional control may be exerted at the level of the motoneuron, as evidenced by apparent neurotensin fiber innervation of presumptive cardiac preganglionic neurons. Similarly, the distribution of neurotensin fibers suggests that the peptide may be acting in gastric regulatory areas of the NTS or on vagal secretomotor neurons to regulate gastric acid secretion.     

Innervation of the nucleus of the solitary tract and the dorsal vagal nucleus by thyrotropin-releasing hormone-containing raphe neurons

The nucleus of the solitary tract and the dorsal vagal nucleus are richly innervated by thyrotropin-releasing hormone (TRH)-containing fibers arising from the caudal raphe nuclei. After transection of vertically oriented fibers by a horizontal knife-cut in the medulla oblongata, TRH-staining disappeared from the vagal nuclei while it increased in transected nerve fibers ventral to the knife-cut. TRH-containing cells are mainly located in the nucleus raphe pallidus and raphe obscurus. TRH-containing fibers run dorsally within the raphe and enter the dorsal vagal complex at its rostral tip. Then they turn caudally and send branches laterally. Immediately caudal to the level of the obex, several TRH-containing fibers cross over the central canal. Cells in regions other than the raphe (hypothalamus or other rostral areas, ventrolateral medulla, cranial nerves) must contribute little to the TRH innervation of the nucleus of the solitary tract and dorsal vagal nucleus, since various knife-cuts transecting all above possible connections did not alter the TRH innervation pattern or TRH concentrations of these vagal nuclei.     

Alpha-2A-adrenergic receptors are present on neurons in the central nucleus of the amygdala that project to the dorsal vagal complex in the rat

The descending pathway between the central nucleus of the amygdala (CeA) and the dorsal vagal complex (DVC) is an important substrate for autonomic functions associated with emotion. Activity in this circuit is crucially modulated by catecholamines and agonists of the alpha-2A-adrenergic receptor (alpha(2A)-AR), which relieve cardiovascular and gastrointestinal symptoms associated with experience of aversive stimuli. The subcellular distribution of alpha(2A)-AR within the CeA, however, has not been characterized. It is also not known if any alpha(2A)-AR-expressing neurons in the CeA project to the dorsal vagal complex. In order to address these questions, we examined the immunocytochemical labeling of alpha(2A)-AR in the CeA of rats receiving microinjection of the retrograde tracer fluorogold (FG) into the dorsal vagal complex at the level of the area postrema, an area involved in cardiorespiratory and gastrointestinal functions. Of all alpha(2A)-AR-labeled profiles in the CeA, the majority were either dendrites (42%) or somata (24%). alpha(2A)-AR labeling was often present on the plasmalemma in dendrites and was mainly found in endosome-like organelles in somata. Of all alpha(2A)-AR immunoreactive somata, 62% also contained immunolabeling for FG and 23% of all dendrites also showed labeling for the retrograde tracer. The intracellular distribution of alpha(2A)-AR did not differ in somata or dendrites with or without detectable FG. The remaining singly labeled alpha(2A)-AR profiles consisted of axons (11%), axon terminals (12%), and glial processes (13%). In numerous instances, alpha(2A)-AR-labeled glia or axon terminals were apposed to DVC projecting neurons. Together, this evidence suggests that the principal site for alpha(2A)-AR activation is at extrasynaptic sites on dendrites of CeA neurons, many of which project to the DVC and also show endosomal receptor labeling. In addition, these results indicate that activation of alpha(2A)-AR in the CeA may influence the activity of DVC projecting neurons through indirect mechanisms, including changes in presynaptic transmitter release or glial function. These results suggest that alpha(2A)-AR agonists in the CeA may modulate numerous processes including stress-evoked autonomic reactions and feeding behavior.     

Medullary sites mediating some abdominal vagal reflexes in the ferret using [C]2-deoxyglucose

The central projections of some abdominal visceral afferents passing through the vagal communicating branch were studied in anesthetized ferrets using [¹⁴C]2-deoxyglucose autoradiography. The reflex effects of electrical stimulation of the vagal communicating branch were studied while measurements of jejunal motor activity and transmural potential difference, a marker of electrogenic epithelial transport were made concurrently. The aim of this study was to examine brainstem projections of some afferent fibers in the communicating branch of the thoracic vagus nerve that are necessary for the reflex regulation of small intestinal motor activity and epithelial transport. In urethane-anesthetized ferrets, electrical stimulation of the cur central end of the vagal communicating branch increased jejunal motor activity and electrogenic epithelial transport. In addition, glucose utilization in the left medial sub-nucleus of the nucleus tractus solitarius and the dorsal motor nucleus of the vagus was significantly increased as compared with sham-operated non-stimulated control animals. Identical areas on the contralateral side of the brain showed no change in glucose utilization as compared with sham-operated non-stimulated controls. This functional brain-mapping study strongly suggests that the left medial sub-nucleus tractus solitarius and the dorsal motor nucleus of the vagus, in the ferret, are involved in processing alimentary affrent activity from both the small intestinal musculature and epithelium as well as the reflex changes in efferent vagal nerve activity to the same regions of the alimentary tract.     

Immunocytochemical characterization of rat brainstem neurons with vagal afferent input from the stomach challenged by acid or ammonia

Exposure of the gastric mucosa to backdiffusing acid is signalled to the brainstem via vagal afferents. This study examined whether exposure of the Sprague-Dawley rat stomach to hydrochloric acid (HCl) or ammonium hydroxide (NH4OH), a noxious chemical produced by Helicobacter pylori, activates different vagal afferent pathways as reflected by different circuitries in the medullary brainstem. Two hours after intragastric treatment with HCl or NH4OH the activation of neurons in the nucleus tractus solitarii at the rostrocaudal extension of the area postrema (NTSAP) was visualized by c-Fos immunohistochemistry and their chemical coding characterized by double-labelling immunohistochemistry. Exposure of the rat gastric mucosa to HCl (0.15-0.5 M) or NH4OH (0.1-0.3 M) led to a concentration-dependent expression of c-Fos in the NTSAP. The number and distribution of NTSAP neurons activated by 0.35 M HCl and 0.3 M NH4OH were similar; the highest number of activated neurons occurring in the medial part of the NTSAP. Some 60% of the NTSAP neurons activated by intragastric HCl and NH4OH stained for the high affinity glutamate transporter EAAC1, while some 30% contained calbindin or neuropeptide Y. Glutamate receptors of the N-methyl-D-aspartate type were found on approximately 50% of the c-Fos-positive cells in the NTSAP, whereas tachykinin NK1, NK2 and NK3 receptors were present on 5-10% of the activated neurons. The similar number and distribution of c-Fos-expressing neurons within the NTSAP and their identical chemical coding indicate that exposure of the rat stomach to backdiffusing concentrations of HCl and NH4OH activates the same vagal afferent-NTSAP pathway.     

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.     

Prenatal ontogeny of substance P-like immunoreactivity in the nucleus tractus solitarii and dorsal motor nucleus of the vagus nerve of the human fetus: an immunocytochemical study

By using immunocytochemical method, the prenatal ontogeny of substance P-like immunoreactivity (SP-LI) was demonstrated in the dorsal motor nucleus of the vagus nerve (nX) and the nucleus tractus solitarii (nTS) of the human fetus at fetal age (menstruation age) of 11.5 weeks to 40 weeks. The time of initial appearance of SP-LI in the human brainstem nTS was between the fetal age 11.5 weeks and 16 weeks. At fetal age 16 weeks, the nTS showed moderate density of SP-LI fibers and terminals in subnucleus dorsalis of the nTS and nX. While the fetus grew, the density of SP-LI in the human fetus brainstem nTS and nX increased gradually from fetal age 16 weeks to 40 weeks. According to the Nissl staining, at fetal age 23 weeks, the nTS of human fetus can be subdivided into dorsal, medial, dorsolateral, ventrolateral and ventral gelatinosus subnuclei. The cytoarchitectonic subdivisions of human fetus nTS is in good agreement with the results obtained by immunocytochemical staining. These findings indicated that substance P (SP) might play an important role in the development of human brainstem nX, nTS, their related cranial nerves, and in their functional establishment during the pranatal period.