Inhibition of transient lower esophageal sphincter relaxation and gastroesophageal reflux by metabotropic glutamate receptor ligands

BACKGROUND & AIMS: Transient lower esophageal sphincter relaxation (TLESR) is the major mechanism of gastroesophageal acid reflux. TLESR is mediated via vagal pathways, which may be modulated by metabotropic glutamate receptors (mGluRs). Group I mGluRs (mGluR1 and 5) have excitatory effects on neurons, whereas group II (mGluR2 and 3) and group III (mGluR4, 6, 7, and 8) are inhibitory. This study determined the effect of mGluRs on triggering of TLESR and reflux in an established conscious ferret model. METHODS: Esophageal manometric/pH studies were performed in ferrets with chronic esophagostomies. TLESR were induced by a gastric load of 25 mL glucose (pH 3.5) and 30 mL air. RESULTS: In control treated animals, gastric load induced 3.52 +/- 0.46 TLESRs per 47-minute study, 89.7% of which were associated with reflux episodes (n = 16). The mGluR5 antagonist MPEP inhibited TLESR dose dependently, with maximal 71% +/- 7% inhibition at 35 micromol/kg (n = 9; P < .0001). MPEP also significantly reduced reflux episodes (P < .001) and increased basal lower esophageal sphincter pressure (P < .05). MPEP inhibited swallowing dose dependently, suggesting a common action on trigger mechanisms for swallowing and TLESR. The more selective analogue, MTEP, had more potent effects (90% +/- 6% inhibition TLESR at 40 micromol/kg; n = 8; P < .0001). In contrast, the group I agonist DHPG tended to increase TLESR. The group II agonist (2R, 4R)-APDC was ineffective, whereas the group III agonist L-(AP4 slightly reduced TLESR (33% at 11 micromol/kg; P < .05). The selective mGluR8 agonist (S)-3, 4-DCPG inhibited TLESR by 54% at 15 micromol/kg (P < .01). CONCLUSIONS: mGluR5 antagonists potently inhibit TLESR and reflux in ferrets, implicating mGluR5 in the mechanism of TLESR. mGluR5 antagonists are therefore promising as therapy for patients with GERD.     

Alterations in the brain-gut axis underlying visceral chemosensitivity in Nippostrongylus brasiliensis-infected mice

BACKGROUND & AIMS: Visceral hypersensitivity, a hallmark of irritable bowel syndrome, is generally considered to be mechanosensitive in nature and mediated via spinal afferents. Both stress and inflammation are implicated in visceral hypersensitivity, but the underlying molecular mechanisms of visceral hypersensitivity are unknown. METHODS: Mice were infected with Nippostrongylus brasiliensis (Nb) larvae, exposed to environmental stress and the following separate studies performed 3-4 weeks later. Mesenteric afferent nerve activity was recorded in response to either ramp balloon distention (60 mm Hg), or to an intraluminal perfusion of hydrochloric acid (50 mmol/L), or to octreotide administration (2 micromol/L). Intraperitoneal injection of cholera toxin B-488 identified neurons projecting to the abdominal viscera. Fluorescent neurons in dorsal root and nodose ganglia were isolated using laser-capture microdissection. RNA was hybridized to Affymetrix Mouse whole genome arrays for analysis to evaluate the effects of stress and infection. RESULTS: In mice previously infected with Nb, there was no change in intestinal afferent mechanosensitivity, but there was an increase in chemosensitive responses to intraluminal hydrochloric acid when compared with control animals. Gene expression profiles in vagal but not spinal visceral sensory neurons were significantly altered in stressed Nb-infected mice. Decreased afferent responses to somatostatin receptor 2 stimulation correlated with lower expression of vagal somatostatin receptor 2 in stressed Nb-infected mice, confirming a link between molecular data and functional sequelae. CONCLUSIONS: Alterations in the intestinal brain-gut axis, in chemosensitivity but not mechanosensitivity, and through vagal rather than spinal pathways, are implicated in stress-induced postinflammatory visceral hypersensitivity.     

Different contributions of ASIC channels 1a, 2, and 3 in gastrointestinal mechanosensory function

AIMS: Members of the acid sensing ion channel (ASIC) family are strong candidates as mechanical transducers in sensory function. The authors have shown that ASIC1a has no role in skin but a clear influence in gastrointestinal mechanotransduction. Here they investigate further ASIC1a in gut mechanoreceptors, and compare its influence with ASIC2 and ASIC3. METHODS AND RESULTS: Expression of ASIC1a, 2, and 3 mRNA was found in vagal (nodose) and dorsal root ganglia (DRG), and was lost in mice lacking the respective genes. Recordings of different classes of splanchnic colonic afferents and vagal gastro-oesophageal afferents revealed that disruption of ASIC1a increased the mechanical sensitivity of all afferents in both locations. Disruption of ASIC2 had varied effects: increased mechanosensitivity in gastro-oesophageal mucosal endings, decreases in gastro-oesophageal tension receptors, increases in colonic serosal endings, and no change in colonic mesenteric endings. In ASIC3-/- mice, all afferent classes had markedly reduced mechanosensitivity except gastro-oesophageal mucosal receptors. Observations of gastric emptying and faecal output confirmed that increases in mechanosensitivity translate to changes in digestive function in conscious animals. CONCLUSIONS: These data show that ASIC3 makes a critical positive contribution to mechanosensitivity in three out of four classes of visceral afferents. The presence of ASIC1a appears to provide an inhibitory contribution to the ion channel complex, whereas the role of ASIC2 differs widely across subclasses of afferents. These findings contrast sharply with the effects of ASIC1, 2, and 3 in skin, suggesting that targeting these subunits with pharmacological agents may have different and more pronounced effects on mechanosensitivity in the viscera.     

Localization and activation of glucagon-like peptide-2 receptors on vagal afferents in the rat

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent proglucagon-derived hormone that stimulates intestinal growth through poorly understood paracrine and/or neural pathways. The relationship between GLP-2 action and a vagal pathway is unclear. Our aims were to determine whether 1) the GLP-2 receptor (GLP-2R) is expressed on vagal afferents by localizing it to the nodose ganglia; 2) exogenous GLP-2 stimulates the vagal afferent pathway by determining immunoreactivity for c-fos protein in the nucleus of the solitary tract (NTS); and 3) functional ablation of vagal afferents attenuates GLP-2-mediated intestinal growth in rats maintained with total parenteral nutrition (TPN). A polyclonal antibody against the N terminus of the rat GLP-2R was raised and characterized. The GLP-2R was localized to vagal afferents in the nodose ganglia and confirmed in enteroendocrine cells, enteric neurons, and nerve fibers in the myenteric plexus using immunohistochemistry. Activation of the vagal afferent pathway, as indicated by c-fos protein immunoreactivity in the NTS, was determined by immunohistochemistry after ip injection of 200 microg human GLP-2. GLP-2 induced a significant 5-fold increase in the number of c-fos protein immunoreactive neurons in the NTS compared with saline. Ablation of vagal afferent function by perivagal application of capsaicin, a specific afferent neurotoxin, abolished c-fos protein immunoreactivity, suggesting that activation of the NTS due to GLP-2 is dependent on vagal afferents. Exogenous GLP-2 prevented TPN-induced mucosal atrophy, but ablation of vagal afferent function with capsaicin did not attenuate this effect. This suggests that vagal-independent pathways are responsible for GLP-2 action in the absence of luminal nutrients during TPN, possibly involving enteric neurons or endocrine cells. This study shows for the first time that the GLP-2R is expressed by vagal afferents, and ip GLP-2 activates the vagal afferent pathway.     

Cooperative activation of cultured vagal afferent neurons by leptin and cholecystokinin

To test the hypothesis that leptin can directly activate vagal afferent neurons, we used fluorescence imaging to detect acute changes in cytosolic calcium after leptin application to primary cultures of vagal afferent neurons dissociated from adult rat nodose ganglia. We found that approximately 40% of vagal afferent neurons exposed to leptin (40 ng/ml) responded with rapid and reversible increases in cytosolic calcium. These responses were dependent upon extracellular calcium. As previously reported, about 35% of vagal afferents increase cytosolic calcium in response to the gut-peptide cholecystokinin (CCK). A majority (74%) of neurons that responded to CCK also exhibited increases in cytosolic calcium in response to leptin. In addition, synergistic increases in cytosolic calcium were observed when leptin and CCK were applied in combination. These results demonstrate that leptin acts directly on vagal afferent neurons to trigger acute influxes of extracellular calcium. Our results also suggest cooperation between leptin and CCK in the activation of some vagal afferent neurons. Acute activation of vagal afferents by leptin alone and in combination with CCK may contribute to modulation of visceral reflexes and control of food intake.     

Sensory substance P innervation of the stomach and pancreas. Demonstration of capsaicin-sensitive sensory neurons in the rat by combined immunohistochemistry and retrograde tracing

The sensory innervation of the stomach and pancreas has been identified by retrograde tracing using the fluorescent dye True Blue (Illing, Gross-Umstadt, Federal Republic of Germany), coupled with the immunohistochemical localization of substance P. Labeled cells were visualized in spinal ganglia, nodose ganglia, celiac ganglion, and dorsal motor nucleus of the vagus after injection of True Blue into both stomach and pancreas. Substance P immunoreactivity was found in 35%-50% of gastric spinal afferent neurons and in approximately 15% of pancreatic spinal afferents. In rats treated at birth with the sensory neurotoxin capsaicin there was a reduction of about 70% in True Blue-labeled cells in the spinal and nodose ganglia, and virtually complete loss of substance P in these ganglia. There was also a marked depletion of substance P-immunoreactive fibers in the pancreas, and in the submucosa of the stomach. The results suggest that the substance P-containing spinal afferents that project to the gastric submucosa are an important component of the gastric sensory innervation.     

New insights into neurohormonal regulation of pancreatic secretion

The existence of high- and low-affinity cholecystokinin (CCK)-A receptors on rodent pancreatic acini is well established. Until recently, CCK was believed to act directly on pancreatic acini to stimulate pancreatic secretion in both rodents and humans. However, conclusive evidence that human pancreatic acini lack functional CCK-A receptors has been presented. Despite substantial differences in rodent and human pancreatic physiology, CCK appears to act via vagal cholinergic pathways to mediate pancreatic secretion in both species. Structural and functional evidence suggests that CCK acts on vagal afferent fibers, which may explain how CCK doses that produce physiologic plasma CCK levels act via vagal cholinergic pathways to stimulate pancreatic secretion. Although most knowledge of vagal CCK-A receptors comes from research on rodents, physiologic studies suggest that this information is applicable to humans. In contrast to its effect on satiety, which is mediated by low-affinity vagal CCK-A receptors, CCK acts through high-affinity CCK-A receptors to evoke pancreatic secretion, suggesting that different affinity states of the vagal CCK receptors mediate different digestive functions. Vagal afferent pathways also transmit sensory information about the mechanical and physiochemical state of the digestive tract, mediated in part by serotonin, which, in turn, influences pancreatic secretion. A synergistic interaction between CCK and serotonin at the level of the nodose ganglia may explain the robust postprandial pancreatic secretion despite a modest postprandial increase in plasma CCK. Important physiologically, these findings not only explain discrepancies in previous in vivo vs. in vitro studies, but they revolutionize our current concept of the mechanism of CCK on pancreatic exocrine secretion.     

Modulation of the intracellular calcium concentration in photoreceptor terminals by a presynaptic metabotropic glutamate receptor.

Fast excitatory neurotransmission in the central nervous system is mediated through glutamate acting on ionotropic glutamate receptors. However, glutamate acting on metabotropic glutamate receptors (mGluRs) can also exert an inhibitory action. Here, we report by immunocytochemistry and physiology, to our knowledge, the first glutamate receptor to be found in terminals of photoreceptors in the mammalian retina-the group III metabotropic glutamate receptor mGluR8. Glutamate is the transmitter of photoreceptors, and thus mGluR8 functions as an autoreceptor. Activation of mGluR8 by the group III mGluR agonists L-2-amino-4-phosphonobutyrate and L-serine-O-phosphate, or by glutamate itself, evokes a decrease in the intracellular calcium ion concentration ([Ca(2+)](i)) in isolated photoreceptors. This effect is blocked by the group III mGluR antagonists (RS)-alpha-methyl-4-phosphonophenylglycine and (RS)-alpha-methylserine-O-phosphate. Agonists for other classes of glutamate receptors-N-methyl-D-aspartic acid, quisqualic acid, kainic acid, or (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-have no effect on the [Ca(2+)](i) in isolated photoreceptors. The down-regulation of the [Ca(2+)](i) in photoreceptors by mGluR8 provides evidence for an inhibitory feedback loop at the photoreceptor synapse in the mammalian retina. This negative feedback may be a mechanism for the fine adjustment of the light-regulated release of glutamate from photoreceptors and may serve as a safety device against excitotoxic levels of release at this tonic synapse. Such a mechanism may provide a model for feedback inhibition in other parts of the central nervous system.     

Glutamate induces apoptosis in anterior pituitary cells through group II metabotropic glutamate receptor activation

Glutamate can induce neuronal cell death by activating ionotropic glutamate receptors (iGluRs) as well as metabotropic glutamate receptors (mGluRs). In the present study, we investigated whether glutamate induces apoptosis of cultured anterior pituitary cells from female rats. Glutamate (1 mm) significantly reduced the metabolic activity of viable cells and increased the percentage of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL)-positive cells and caspase-3 activity in anterior pituitary cells. The inhibitory effect of glutamate on the viability of anterior pituitary cells was not observed in the presence of [2S]-alpha-ethylglutamic acid (0.75 mm), a specific group II mGluR antagonist. Also, (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (LCCG-I; 0.75 mm), a specific group II mGluR agonist, reduced viability and increased the percentage of TUNEL-positive anterior pituitary cells. Group I and III mGluRs and iGluRs agonists failed to modify the metabolic activity of anterior pituitary cells. Glutamate and LCCG-I increased the percentage of TUNEL-positive lactotropes and somatotropes. The subunit mGluR2/3, belonging to group II mGluR, was localized in these cell types. Glutamate increased nitric oxide (NO) synthase (NOS) activity and inducible NOS expression in anterior pituitary cells. N-methyl-l-arginine (NMMA, 0.5 mm), a NOS inhibitor, potentiated the apoptotic effect of glutamate in anterior pituitary cells, indicating that NO may restrain glutamate-induced apoptosis. Incubation of anterior pituitary cells with a cAMP analog (N6, 2'-o-dibutyryladenosine 3', 5'-cyclic monophosphate; 1 mm) attenuated the apoptosis induced by glutamate. Glutamate and LCCG-I decreased prolactin release from anterior pituitary cells. N6, 2'-o-dibutyryladenosine 3', 5'-cyclic monophosphate reversed the inhibitory effect of glutamate on prolactin release, but NMMA failed to modify it. Our data show that glutamate induces apoptosis of lactotropes and somatotropes through group II mGluR activation, probably by decreasing cAMP synthesis.     

Metabotropic glutamate and GABAB receptors contribute to the modulation of glucose-stimulated insulin secretion in pancreatic beta cells

Aims/hypothesis: The neurotransmitters glutamate and γ-aminobutyric acid (GABA) could participate in the regulation of the endocrine functions of islets of Langerhans. We investigated the role of the metabotropic glutamate (mGluRs) and GABA_B (GABA_BRs) receptors in this process. Methods: We studied the expression of mGluRs and GABA _BRs in rat and human islets of Langerhans and in pancreatic α-cell and beta-cell lines using RT-PCR and immunoblot analysis. Effects of mGluR and GABA _B R agonists on insulin secretion were determined by radioimmunoassays and enzyme-linked immunoadsorbent assays (ELISAs). Results: We detected mGluR3 and mGluR5 (but not mGluR1, 6 and 7) mRNAs in all of the samples examined. Trace amount of mGluR2 was found in MIN6 beta cells; mGluR4 was identified in rat islets; and mGluR8 expression was detected in rat islets, RINm5F and MIN6 cells. GABA _BR1 a/b and 2 mRNAs were identified in islets of Langerhans and MIN6 cells. The expression of mGluR3, mGluR5, GABA_BR1 a/b and GABA_BR2 proteins was confirmed using specific antibodies. Group I (mGluR1/5) and group II (mGluR2/3) specific mGluR agonists increased the release of insulin in the presence of 3 to 10 mmol/l or 3 to 25 mmol/l glucose, respectively, whereas a group III (mGluR4/6–8) specific agonist inhibited insulin release at high (10–25 mmol/l) glucose concentrations. Baclofen, a GABA_BR agonist, also inhibited the release of insulin but only in the presence of 25 mmol/l glucose. Conclusion/interpretation: These data suggest that mGluRs and GABA_BRs play a role in the regulation of the endocrine pancreas with mechanisms probably involving direct activation or inhibition of voltage dependent Ca²⁺-channels, cAMP generation and G-protein-mediated modulation of K_ATP channels. [Diabetologia (2002) 45: 242–252] Received: 18 September 2001 and in revised form: 5 November 2001     

Angiotensin Receptors and the Vagal System

ABSTRACT

Angiotensin II (Ang II) is known to attenuate the vagal component of the baroreflex at both central and peripheral cardiac sites. Ang II receptor binding sites occur in both the nucleus of the solitary tract (NTS), where they are associated with vagal afferent terminals, and in the dorsal motor nucleus of vagus. In this study we have examined the distribution of Ang II binding sites in the cell bodies of vagal afferents in the nodose ganglion, and investigated whether these receptors are transported in the vagus nerve. Dense Ang II receptor binding was observed over neuronal cell bodies in the nodose ganglion and, in streaks, in the vagus nerve. Vagal ligation distal to the nodose ganglion resulted in a marked accumulation of receptor binding sites, proximal to the ligature, with a moderate increase on the distal side. These results demonstrate that Ang II receptor binding sites occur in the nodose ganglion and are transported centrally in the vagus to be located on presynaptic terminals in the NTS and also peripherally where they may occur on terminals of the vagus.     

Hyperpolarization-activated cyclic nucleotide-gated cation channel subtypes differentially modulate the excitability of murine small intestinal afferents

AIM:To assess the role of hyperpolarization-activated cyclic nucleotide-gated cation(HCN) channels in regulating the excitability of vagal and spinal gut afferents.METHODS:The mechanosensory response of mesenteric afferent activity was measured in an ex vivo murine jejunum preparation.HCN channel activity was recorded through voltage and current clamp in acutely dissociated dorsal root ganglia(DRG) and nodose ganglia(NG) neurons retrogradely labeled from the small intestine through injection of a fluorescent marker(DiI).The isoforms of HCN channels expressed in DRG and NG neurons were examined by immunohistochemistry.RESULTS:Ramp distension of the small intestine evoked biphasic increases in the afferent nerve activity,reflecting the activation of low-and high-threshold fibers.HCN blocker CsCl(5 mmol/L) preferentially inhibited the responses of low-threshold fibers to distension and showed no significant effects on the high-threshold responses.The effect of CsCl was mimicked by the more selective HCN blocker ZD7288(10 μmol/L).In 71.4% of DiI labeled DRG neurons(n = 20) and 90.9% of DiI labeled NG neurons(n = 10),an inward current(I h current) was evoked by hyperpolarization pulses which was fully eliminated by extracellular CsCl.In neurons expressing I h current,a typical "sag" was observed upon injection of hyperpolarizing current pulses in current-clamp recordings.CsCl abolished the sag entirely.In some DiI labeled DRG neurons,the I h current was potentiated by 8-Br-cAMP,which had no effect on the I h current of DiI labeled NG neurons.Immunohistochemistry revealed differential expression of HCN isoforms in vagal and spinal afferents,and HCN 2 and HCN 3 seemed to be the dominant isoform in DRG and NG,respectively.CONCLUSION:HCNs differentially regulate the excitability of vagal and spinal afferent of murine small intestine.     

Antigen inhalation unmasks NK-2 tachykinin receptor-mediated responses in vagal afferents

The majority of airway sensory innervation originates from afferent neurons whose somata reside in vagal (nodose and jugular) ganglia. Using guinea pigs immunized with chick ovalbumin, we have discovered that airway inflammation provokes phenotypic changes in the tachykinin responsiveness of nodose neurons. Bath application of substance P (SP; 0.1 to 10 microM) to nodose neurons isolated from guinea pigs with normal uninflamed airways did not elicit measurable changes in resting electrophysiological properties. In sharp contrast, 80% of nodose neurons isolated 24 h after in vivo aerosolized antigen challenge of the airway were depolarized by 100 nM SP. Inhalation of a nonantigenic protein did not evoke the expression of SP responses. Pharmacological analysis revealed that SP responses unmasked by airway inflammation were mediated by neurokinin-2 (NK-2) tachykinin receptors. There are several potential mechanisms for transduction of an "unmasking signal" from the inflamed airway to vagal afferent somata. The vagus nerve may relay the signal, either through anterograde transport and/or nerve impulse activity. Alternatively, a signal generated by airway inflammation may be carried by the circulation to the nodose ganglia. Unilateral vagotomy significantly reduced the percentage of SP-responsive neurons compared with intact controls, suggesting that the vagus nerve is required for unmasking of NK-2 responses.     

Somatostatin sst(2) receptor-mediated inhibition of mesenteric afferent nerves of the jejunum in the anesthetized rat

BACKGROUND & AIMS: Octreotide inhibits visceral sensations in clinical studies, but the site of action and the receptor type(s) involved are unknown. Our aim was to investigate the effects of octreotide, the selective sst(2) receptor agonist (BIM 23027), and the sst(2) antagonist (Cyanamid154806) on the activity of mesenteric afferent fibers innervating the rat jejunum. Their effects were investigated on baseline discharge, mechanosensitivity, and responses to algesic chemicals. METHODS: Extracellular multiunit recordings of jejunal afferent nerve firing were made in pentobarbitone-anesthetized (60 mg/kg intraperitoneally) male Wistar rats. RESULTS: Octreotide and BIM23027 (0.001-100 microg/kg intravenously) each evoked a long-lasting inhibition of baseline discharge, which was blocked by cyanamid 154806 (3 mg/kg) and absent in chronically vagotomized animals. Afferent responses to bradykinin were also inhibited by an sst(2) receptor-mediated mechanism but were unaffected by vagotomy. Ramp distentions of the jejunum evoked a biphasic activation of afferent nerve discharge, the low threshold component of which was attenuated in vagotomized animals. Sst(2) receptor agonists significantly inhibited the mechanosensitivity of spinal, but not vagal, afferents. CONCLUSIONS: These data suggest that activation of somatostatin sst(2) receptors inhibit populations of mesenteric afferents likely to be involved in nociceptive transmission.     

帕金森病模型大鼠海马mGluR5的表达变化及意义

目的探讨帕金森病(PD)模型大鼠海马mGluR5的表达变化及意义。方法将SD大鼠随机分为正常对照组(A组)、PD模型组(B组)和非竞争性NMDA受体拮抗剂D-AP-5+PD组(C组),通过免疫组织化学方法观察多克隆抗体mGluR5在大鼠海马的表达变化。结果正常对照组中大鼠海马有丰富的mGluR5表达;PD模型组中大鼠海马mGluR5表达明显下降;在非竞争性NMDA受体拮抗剂D-AP-5+PD组中,大鼠海马mGluR5表达又明显上调。结论帕金森病模型大鼠海马各区mGluR5表达下降,可能是神经细胞的一种自我保护作用。mGluR5可能与帕金森病认知和情感及记忆功能障碍有关。帕金森病模型大鼠海马各区经用非竞争性NMDA受体拮抗剂D-AP-5处理后,海马mGluR5表达明显上调,推测mGluR5表达下降可能在帕金森病长时程增强(LTP)诱导过程中具有重要作用,其作用机制可能为NMDA受体依赖性。     

Identification and substance P content of vagal afferent neurons innervating the epithelium of the guinea pig trachea.

Both the nodose and jugular vagal ganglia provide sensory innervation to the airways. The purpose of this study was to localize and characterize the substance P (SP) content of vagal afferent neurons that project specifically to the tracheal epithelium. A retrograde neuronal tracer, fast blue dye or rhodamine-labeled latex microspheres, was instilled into the guinea pig trachea. After 7 d, the nodose and jugular ganglia were removed, sectioned, and prepared for immunocytochemistry. Sections of tracheal mucosa demonstrated that fast blue dye diffused throughout the airway wall, whereas the rhodamine-labeled microspheres, as expected, did not penetrate the basement membrane and were thus localized to the epithelium. When the diffusible fast blue dye was used, approximately 60% of the labeled neurons were found in the nodose ganglia and 40% in the jugular ganglia. By contrast, when the beads were used to label only epithelial nerve fibers, 97 +/- 1% of the tracheal neurons taking up the dye were derived from jugular neurons, 60 +/- 6% of which contained SP immunoreactivity. These studies demonstrate that, in contrast to the submucosa, nerve fibers innervating the epithelium of the trachea are derived nearly exclusively from neurons with cell bodies in the jugular ganglia.     

CCK-induced reduction of food intake and hindbrain MAPK signaling are mediated by NMDA receptor activation

The dorsal vagal complex of the hindbrain, including the nucleus of the solitary tract (NTS), receives neural and humoral afferents that contribute to the process of satiation. The gut peptide, cholecystokinin (CCK), promotes satiation by activating gastrointestinal vagal afferents that synapse in the NTS. Previously, we demonstrated that hindbrain administration of N-methyl-D-aspartate (NMDA)-type glutamate receptor antagonists attenuate reduction of food intake after ip CCK-8 injection, indicating that these receptors play a necessary role in control of food intake by CCK. However, the signaling pathways through which hindbrain NMDA receptors contribute to CCK-induced reduction of food intake have not been investigated. Here we report CCK increases phospho-ERK1/2 in NTS neurons and in identified vagal afferent endings in the NTS. CCK-evoked phospho-ERK1/2 in the NTS was attenuated in rats pretreated with capsaicin and was abolished by systemic injection of a CCK1 receptor antagonist, indicating that phosphorylation of ERK1/2 occurs in and is mediated by gastrointestinal vagal afferents. Fourth ventricle injection of a competitive NMDA receptor antagonist, prevented CCK-induced phosphorylation of ERK1/2 in hindbrain neurons and in vagal afferent endings, as did direct inhibition of MAPK kinase. Finally, fourth ventricle administration of either a MAPK kinase inhibitor or NMDA receptor antagonist prevented the reduction of food intake by CCK. We conclude that activation of NMDA receptors in the hindbrain is necessary for CCK-induced ERK1/2 phosphorylation in the NTS and consequent reduction of food intake.     

Role of visceral afferent mechanisms in functional bowel disorders

This report analyzes the clinical and physiological evidence supporting a role for altered visceral afferent mechanisms in the pathogenesis of two functional bowel syndromes: noncardiac chest pain and the irritable bowel syndrome. Considerable recent evidence indicates that increased contractility is present only in a minority of patients and that hypercontractile episodes are not temporally related to abdominal pain. In contrast, altered sensation and motor reflexes in response to physiological stimuli, such as mechanical distention or acid, is common when appropriately investigated. The vagal and spinal afferent innervation mediates visceral sensation and is involved in multiple reflex loops regulating gastrointestinal effector function, such as motility and secretion. Sensory input can be modulated peripherally at the afferent nerve terminal, at the level of prevertebral ganglia, the spinal cord, and the brainstem. An up-regulation of afferent mechanisms would result both in altered conscious perception of physiological stimuli and in altered motor reflexes. Current evidence is consistent with an alteration in the peripheral functioning of visceral afferents and/or in the central processing of afferent information in the etiology of altered somatovisceral sensation and motor function observed in patients with functional bowel disease.