Mucosal acid challenge activates nitrergic neurons in myenteric plexus of rat stomach (original) (raw)
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European Journal of Neuroscience, 2004
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 (NH 4 OH), a noxious chemical produced by Helicobacter pylori , activates different vagal afferent pathways as re¯ected by different circuitries in the medullary brainstem. Two hours after intragastric treatment with HCl or NH 4 OH the activation of neurons in the nucleus tractus solitarii at the rostrocaudal extension of the area postrema (NTS AP ) 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 NH 4 OH (0.1±0.3 M) led to a concentration-dependent expression of c-Fos in the NTS AP . The number and distribution of NTS AP neurons activated by 0.35 M HCl and 0.3 M NH 4 OH were similar; the highest number of activated neurons occurring in the medial part of the NTS AP . Some 60% of the NTS AP neurons activated by intragastric HCl and NH 4 OH stained for the high af®nity 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 NTS AP , whereas tachykinin NK 1 , NK 2 and NK 3 receptors were present on 5±10% of the activated neurons. The similar number and distribution of c-Fos-expressing neurons within the NTS AP and their identical chemical coding indicate that exposure of the rat stomach to backdiffusing concentrations of HCl and NH 4 OH activates the same vagal afferent ± NTS AP pathway.
Animals
The enteric nervous system (ENS) is the part of the nervous system that is located in the wall of the gastrointestinal tract and regulates the majority of the functions of the stomach and intestine. Enteric neurons may contain various active substances that act as neuromediators and/or neuromodulators. One of them is a gaseous substance, namely nitric oxide (NO). It is known that NO in the gastrointestinal (GI) tract may possess inhibitory functions; however, many of the aspects connected with the roles of this substance, especially during pathological states, remain not fully understood. An experiment is performed here with 15 pigs divided into 3 groups: C group (without any treatment), C1 group (“sham” operated), and C2 group, in which experimental inflammation was induced. The aim of this study is to investigate the influence of inflammation on nitrergic nervous structures in the muscular layer of the porcine descending colon using an immunofluorescence method. The obtained resul...
Pain, 2001
Noxious challenge of the rat gastric mucosa by hydrochloric acid (HCl) is signaled to the nucleus tractus solitarii (NTS) and area postrema (AP). This study examined the participation of glutamate and tachykinins in the medullary transmission process. Activation of neurons was visualized by in situ hybridization autoradiography of c-fos messenger RNA (mRNA) 45 min after intragastric (IG) administration of 0.5 M HCl or saline. IG HCl caused many neurons in the NTS and some neurons in the AP to express c-fos mRNA. The NMDA glutamate receptor antagonist MK-801 (2 mg/kg), the NK 1 tachykinin receptor antagonist GR-205,171 (3 mg/kg) and the NK 2 receptor antagonist SR-144,190 (0.1 mg/kg) failed to signi®cantly reduce the NTS response to IG HCl, whereas the triple combination of MK-801, 190 inhibited it by 45±50%. Only in rats that had been preexposed IG to HCl 48 h before the experiment was MK-801 alone able to depress the NTS response to IG HCl. In contrast, the c-fos mRNA response in the AP was signi®cantly augmented by MK-801, an action that was prevented by coadministration of 190. Inhibition of neuronal nitric oxide synthase with 7-nitroindazole (45 mg/kg) was without effect on the IG HCl-evoked c-fos mRNA expression in the NTS and AP. Our data show that glutamate acting via NMDA receptors and tachykinins acting via NK 1 and NK 2 receptors cooperate in the vagal afferent input from the acid-threatened stomach to the NTS and participate in the processing of afferent input to the AP in a different and complex manner. These opposing interactions in the AP and NTS and the increase in NMDA receptor function in the NTS after a gastric acid insult are likely to have a bearing on the neuropharmacology of dyspepsia.
Neurogastroenterology & Motility, 2001
During intestinal in¯ammation, motility disturbances are not restricted to in¯amed regions, but may also occur in remote non-in¯amed sites of the gastrointestinal tract. Our aim was to investigate the motor function of the gastric fundus after the induction of terminal ileitis in the rat. Ileal in¯ammation was induced by intraluminal installation of 2,4,6-trinitrobenzenesulphonic acid (TNBS) into the ileum. In¯ammation was assessed both histologically and biochemically. Contractions and relaxations of longitudinal muscle strips from the gastric fundus were studied 36 h and 1 week later. During the acute phase of ileal in¯ammation (36 h), the non-in¯amed stomach was distended. The contractility of longitudinal muscle strips of the gastric fundus was decreased due to a post-receptor defect. In addition, nonadrenergic noncholinergic (NANC) relaxations were inhibited due to neuronal dysfunction. Aortic contractility remained normal and the mere presence of food in the stomach did not account for the disturbed neuromuscular function in the gastric fundus. Ablation of extrinsic primary afferent neurones by capsaicin further impaired gastric fundus contractility. Transection and re-anastomosis of the jejunum reversed the effect of TNBS-induced ileitis on the neuromuscular function of the gastric fundus. One week after TNBS, cholinergic neurotransmission was increased in the gastric fundus. During acute ileitis, smooth muscle cell contractility and inhibitory NANC neurotransmission are inhibited in the non-in¯amed gastric fundus. This phenomenon may be mediated by intrinsic connections within the enteric nervous system.
American Journal of Physiology-Gastrointestinal and Liver Physiology, 1997
Responses of myenteric AH and S neurons to local application of chemicals to the mucosa of the guinea pig small intestine were obtained using conventional intracellular recording techniques. Preparations were dissected to reveal the myenteric plexus over one-half of the circumference of the gut with intact mucosa on the the half. Neurons were impaled within the exposed one-half, whereas potential stimulants, in buffered saline, were transiently applied to the mucosa, 1-1.5 mm circumferential from the impalement. The stimulants elicited action potentials (AP) in AH neurons that did not arise from synaptic activity. AH neurons also responded with slow excitatory postsynaptic potentials (EPSP). S neurons were activated synaptically, via fast and slow EPSP, but not nonsynaptically. Mucosal application of solutions of a low pH (3-5) or a high pH (9-11) were both effective stimulants. Solutions of a neutral pH, which was also a control for mild mechanical stimulation, were usually ineffec...
Pain, 2001
Although gastric acid is a factor in upper abdominal pain, the signaling and processing of a gastric mucosal acid insult within the brain are not known. This study examined which nuclei in the rat brain respond to challenge of the gastric mucosa by a noxious concentration of hydrochloric acid (HCl) and whether the central input is carried by vagal afferent neurons. Activation of neurons in the brain was mapped by in situ hybridization autoradiography of messenger ribonucleic acid (mRNA) for the immediate early gene c-fos 45 min after intragastric administration of saline or HCl. Following intragastric HCl (0.5 M) challenge, many neurons in the nucleus tractus solitarii, lateral parabrachial nucleus, thalamic and hypothalamic paraventricular nucleus, supraoptic nucleus, central amygdala and medial/lateral habenula expressed c-fos mRNA as compared to intragastric treatment with saline (0.15 M). However, c-fos transcription in the insular cortex was not enhanced by the gastric acid insult. Hypertonic saline (0.5 M) caused only a minor expression of c-fos mRNA in the hypothalamus and amygdala. The acid-evoked c-fos induction in subcortical nuclei was depressed by at least 80% five days after bilateral subdiaphragmatic vagotomy. Collectively, these observations indicate that vagal afferent input from the acid-threatened gastric mucosa does not reach the insular cortex but leads to activation of subcortical brain nuclei that are involved in emotional, behavioral, neuroendocrine, autonomic and antinociceptive reactions to a noxious stimulus.
Acid-Sensing Properties in Rat Gastric Sensory Neurons from Normal and Ulcerated Stomach
Journal of Neuroscience, 2005
Gastric acid contributes to dyspeptic symptoms, including abdominal pain, in patients with disorders of the proximal gastrointestinal tract. To examine the molecular sensor(s) of gastric acid chemonociception, we characterized acid-elicited currents in dorsal root ganglion (DRG) and nodose ganglion (NG) neurons that innervate the stomach and examined their modulation after induction of gastric ulcers. A fluorescent dye (DiI) was injected into the stomach wall to retrogradely label gastric sensory neurons. After 1-2 weeks, gastric ulcers were induced by 45 s of luminal exposure of the stomach to 60% acetic acid injected into a clamped area of the distal stomach; control animals received saline. In whole-cell voltage-clamp recordings, all gastric DRG neurons and 55% of NG neurons exhibited transient, amiloride-sensitive, acid-sensing ion-channel (ASIC) currents. In the remaining 45% of NG neurons, protons activated a slow, sustained current that was attenuated by the transient receptor potential vanilloid subtype 1 antagonist, capsazepine. The kinetics and proton sensitivity of amiloride-sensitive ASIC currents differed between NG and DRG neurons. NG neurons had a lower proton sensitivity and faster kinetics, suggesting expression of specific subtypes of ASICs in the vagal and splanchnic innervation of the stomach. Effects of Zn 2ϩ and N,N,N,N-tetrakis-(2-pyridylmethyl)-ethylenediamine on acid-elicited currents suggest contributions of ASIC1a and ASIC2a subunits. Gastric ulcers altered the properties of acid-elicited currents by increasing pH sensitivity and current density and changing current kinetics in gastric DRG neurons. The distinct properties of NG and DRG neurons and their modulation after injury suggest differential contributions of vagal and spinal afferent neurons to chemosensation and chemonociception.
Nitrergic Enteric Neurons in Health and Disease—Focus on Animal Models
International Journal of Molecular Sciences
Nitrergic enteric neurons are key players of the descending inhibitory reflex of intestinal peristalsis, therefore loss or damage of these neurons can contribute to developing gastrointestinal motility disturbances suffered by patients worldwide. There is accumulating evidence that the vulnerability of nitrergic enteric neurons to neuropathy is strictly region-specific and that the two main enteric plexuses display different nitrergic neuronal damage. Alterations both in the proportion of the nitrergic subpopulation and in the total number of enteric neurons suggest that modification of the neurochemical character or neuronal death occurs in the investigated gut segments. This review aims to summarize the gastrointestinal region and/or plexus-dependent pathological changes in the number of nitric oxide synthase (NOS)-containing neurons, the NO release and the cellular and subcellular expression of different NOS isoforms. Additionally, some of the underlying mechanisms associated wit...
Regulatory mechanism of acid secretion in the damaged stomach: Role of endogenous nitric oxide
Journal of Gastroenterology and Hepatology, 2000
15 (Suppl.) D37-D45 protect the stomach against subsequent challenge with necrotizing agents. Previous studies have shown that the gastric alkaline response incurred in the rat stomach after damage with hypertonic solution results from both the inhibition of acid secretion caused by the release of endogenous prostaglandins (PG) and the increased level of HCO 3 and that these factors play a role in the functional and morphological NITRIC OXIDE, HELICOBACTER PYLORI AND GASTROINTESTINAL DISORDERS Abstract The present article overviews the regulatory mechanism of acid secretion in the stomach after damage with taurocholate (TC), one of the bile acids. Mucosal exposure of a rat stomach to 20 mmol/L TC for 30 min caused a decrease of acid secretion with a concomitant increase in nitric oxide (NO) and prostaglandin (PG) E 2 (PGE 2 ) as well as Ca 2+ in the luminal contents. Prior administration of N G -nitro-L-arginine methyl ester (L-NAME), as well as indomethacin, significantly attenuated the reduction of acid secretion by TC and acid secretion was even increased in the presence of L-NAME. The acid stimulatory effect of L-NAME in the damaged stomach was not mimicked by aminoguanidine and was antagonized by co-administration of L-arginine but not D-arginine. Increased NO release in the damaged stomach was suppressed by pretreatment with L-NAME or co-application of EGTA and the latter also inhibited the increase in luminal Ca 2+ . The enhanced acid secretory response in the presence of L-NAME was also inhibited by cimetidine, FPL-52694 (a mast cell stabilizer) or sensory deafferentation. Mucosal exposure to TC caused an increase in luminal histamine output, together with a decrease in the number of mucosal mast cells in the stomach. These changes were prevented by FPL-52694 and sensory deafferentation and were also partly suppressed by indomethacin. In addition, the acid stimulatory action of L-NAME in the damaged stomach was significantly mitigated when indomethacin was administered together with L-NAME. We conclude that: (i) damage in the stomach may activate acid a stimulatory pathway in addition to a PG-, NO-and Ca 2+ -dependent inhibitory mechanism, but the latter effect overcomes the former, resulting in a decrease in acid secretion; (ii) acid stimulation in the damaged stomach is mediated by histamine released from the mucosal mast cell, a process interacting with capsaicin-sensitive sensory nerves; (iii) the increase in luminal Ca 2+ plays a role in increasing NO production and, hence, in regulating acid secretion; and (iv) PG may have a dual role in the regulation of acid secretion in the damaged stomach: an inhibitory effect at the parietal cell and an excitatory effect, probably through enhancing the release of mucosal histamine.
Gut, 2007
Background and aims: Patients with inflammatory bowel disease often present with abnormal gut motility away from the inflammatory site. We studied remote motility disturbances and their pathophysiology in a rat model of colitis. Methods: Colitis was induced 72 h prior to experiments using trinitrobenzene sulphate (TNBS) instillation. Inflammation was verified using histology and myeloperoxidase (MPO) measurements. To assess gut motility, we determined gastric emptying, distal front and geometric centre (GC) of intestinal transit 30 min after intragastric administration of a semiliquid Evans blue solution. The effects of hexamethonium (20 mg/kg), capsaicin (125 mg/kg) and pelvic nerve section on colitis induced motility changes were evaluated. c-Fos expression was studied in the pelvic nerve dorsal root ganglion (DRG) S1. Results: Colitis reduced gastric emptying from 38.4 (3.6)% in controls to 22.7 (4.4)% in TNBS treated rats in the absence of local gastric inflammation. Colitis had no effect on the distal front or on the geometric centre of small intestinal transit. Hexamethonium reduced gastric emptying in controls to 26.3 (4.1)% but restored it to 35.8 (4.4)% in TNBS treated rats. Capsaicin significantly impaired gastric emptying in controls from 33.1 (5.2)% to 9.5 (3.3)% while this effect was less pronounced in TNBS treated rats (from 19.2 (2.3)% to 11.5 (3.8)%; NS). In TNBS treated rats, pelvic nerve section completely restored gastric emptying from 19.8 (5.3)% to 52.5 (6.3)% without any effect on gastric emptying in control rats. TNBS colitis induced de novo c-Fos expression in the DRG S1. Conclusions: Experimental colitis in rats delays gastric emptying via a neuronal pathway involving pelvic afferent nerve hyperactivity.