Changes in colonic motility and the electrophysiological properties of myenteric neurons persist following recovery from trinitrobenzene sulfonic acid colitis in the guinea pig

Persistent changes in gastrointestinal motility frequently accompany the resolution of colitis, through mechanisms that remain to be determined. Trinitrobenzene sulfonic acid (TNBS) colitis in the guinea pig decreases the rate of propulsive motility, causes hyperexcitability of AH neurons, and induces synaptic facilitation. The changes in motility and AH neurons are sensitive to cyclooxygenase-2 (COX-2) inhibition. The aim of this investigation was to determine if the motility and neurophysiological changes persist following recovery from colitis. Evaluations of inflammation, colonic motility and intracellular electrophysiology of myenteric neurons 8 weeks after TNBS administration were performed and compared to matched control conditions. Myeloperoxidase levels in the colons were comparable to control levels 56 days after TNBS treatment. At this time point, the rate of colonic motility was decreased relative to controls following treatment with TNBS alone or TNBS plus a COX-2 inhibitor. Furthermore, the electrical properties of AH neurons and fast synaptic potentials in S neurons were significantly different from controls and comparable to those detected during active inflammation. Collectively, these data suggest that altered myenteric neurophysiology initiated during active colitis persists long term, and provide a potential mechanism underlying altered gut function in individuals during remission from inflammatory bowel disease.     

Induction of neuronal nitric oxide synthase by sympathetic denervation is mediated via alpha 2-adrenoceptors in the jejunal myenteric plexus

Nitric oxide (NO) is an important nonadrenergic, non-cholinergic (NANC) inhibitory neurotransmitter in the gastrointestinal tract. In previous studies, neuronal nitric oxide synthase (nNOS) in the jejunal myenteric plexus, a key enzyme responsible for the release of NO, has been demonstrated to increase after splanchinic ganglionectomy (sympathetic nerve transection). The alpha2-adrenoceptor is known to be one of the most important receptors which controls intestinal motility. In the present study, we examined the effect of application of the alpha2-adrenoceptor agonist, clonidine hydrochloride, on nNOS expression in the rat jejunal myenteric plexus after splanchinic ganglionectomy. Clonidine (0.1-1 mg/kg, i.p.) or saline was administered for 5 days after the splanchinic ganglionectomy. The nNOS expression and nNOS mRNA were detected by immunohistochemistry and in situ hybridization for nNOS mRNA, respectively. In the rats treated with vehicle after the splanchinic ganglionectomy, nNOS expression in the myenteric plexus significantly increased compared with sham-operated rats. The increases in nNOS protein and mRNA after splanchinic ganglionectomy were significantly reversed by clonidine treatment. Clonidine-treated naive rats showed no difference in nNOS expression compared with sham-operated rats. These data suggest that nNOS expression in the jejunal myenteric plexus after splanchinic ganglionectomy is regulated by the alpha2-adrenoceptor and that the alpha2-adrenoceptor may play an important role in abnormal intestinal motility following splanchinic ganglionectomy in rat jejunum.     

Altered myoelectrical activity in noninflamed ileum of rats with colitis induced by trinitrobenzene sulphonic acid

Changes in gastric emptying and orocaecal transit time in patients with ulcerative colitis suggest that disturbances in gut motility may not be restricted to inflamed sites. This study sought to characterize changes in the motility of noninflamed ileum in a rat colitis model and to explore the mechanism(s) potentially involved. The myoelectrical activity of the ileum was recorded in rats with trinitrobenzene sulphonic acid (TNBS)-induced colitis. The degree of ileal and colonic inflammation was assessed by quantification of macroscopic damage and myeloperoxidase activity (MPO). The effect on ileal motility of pretreatment with atropine, indomethacin and NG-nitro-L-arginine-methyl ester (L-NAME) was investigated. TNBS-induced inflammation was restricted to the distal colon, as evidenced by morphological scores and MPO. Colitis was associated with increased frequency of ileal migrating motor complexes, characterized mainly by a decrease in the duration of phases I and III. The occurrence of ileal giant migrating complexes remained unchanged. The myoelectrical changes observed in the ileum persisted after treatment with atropine, indomethacin and L-NAME. Distal colitis is associated with abnormal myoelectrical activity in the noninflamed ileum of rats. Neither acetylcholine nor prostaglandins and nitric oxide seem to be involved.     

Morphometric evaluation of oesophageal wall in patients with nutcracker oesophagus and ineffective oesophageal motility

Abstract  The pathogenesis of nutcracker oesophagus (NE) and ineffective oesophageal motility (IEM) is unclear. Damage to the enteric nervous system or smooth muscle can cause oesophageal dysmotility. We tested the hypothesis that NE and IEM are associated with abnormal muscular or neural constituents of the oesophageal wall. Oesophageal manometry was performed in patients prior to total gastrectomy for gastric cancer. The oesophageal manometries were categorized as normal ( n  = 7), NE ( n  = 13), or IEM ( n  = 5). Histologic examination of oesophageal tissue obtained during surgery was performed after haematoxylin and eosin (H&E) and trichrome staining. Oesophageal innervation was examined after immunostaining for protein gene product-9.5 (PGP-9.5), choline acetyltransferase (ChAT) and neuronal nitric oxide synthase (nNOS). There were no significant differences in inner circular smooth muscle thickness or degree of fibrosis among the three groups. Severe muscle fibre loss was found in four of five patients with IEM. The density of PGP-9.5-reactive neural structures was not different among the three groups. The density of ChAT immunostaining in the myenteric plexus (MP) was significantly greater in patients with NE ( P  < 0.05) and the density of nNOS immunostaining in the circular muscle (CM) was significantly greater in IEM patients ( P  < 0.05). The ChAT/nNOS ratio in both MP and CM was significantly greater in NE patients. NE may result from an imbalance between the excitatory and inhibitory innervation of the oesophagus, because more than normal numbers of ChAT-positive myenteric neurones are seen in NE. Myopathy and/or increased number of nNOS neurones may contribute to the hypocontractile motor activity of IEM.     

Alterations of neurokinin receptors and interstitial cells of Cajal during and after jejunal inflammation induced by Nippostrongylus brasiliensis in the rat

Substance P (SP) and its receptors NK1 and NK2 are widely expressed in the intestinal wall by neurones, interstitial cells of Cajal (ICC) and smooth muscle cells. Changes in SP and/or its NK receptors have been documented during experimental inflammation in animals or inflammatory bowel diseases in humans, but the data concern the acute phase of the inflammatory process. We determined immunohistochemically whether NK receptors and SP were altered in the muscle coat during jejunal inflammation induced by the nematode Nippostrongylus brasiliensis and whether these alterations persisted when inflammation had spontaneously resolved 30 days postinfection. An ultrastructural analysis was also conducted on ICC, nerves and muscle. At day 14, when inflammation peaked, there was a reduction in NK1 receptors in myenteric neurones and in SP-immunoreactive nerve endings. There were also ultrastructural anomalies in synaptic vesicles and NK2 receptor loss in the circular muscle layer. The SP decrease persisted at day 30, whereas neurones and circular muscle cells re-expressed NK1 and NK2 receptors, respectively. The ICC at the deep muscular plexus, located near to the inflammatory site, underwent alterations leading to their complete loss at day 30. These morphological changes are probably associated with impairment in tachykinergic control of jejunal functions leading to the alterations of motility and sensitivity to distension already described in these animals.     

The effect of nitric oxide donors on nitric oxide synthase-expressing myenteric neurones in culture.

Previously, we demonstrated that intestinal inflammation leads to a postinflammatory loss of nitric oxide synthase (NOS)-expressing myenteric neurones and motility disturbances. Here, we investigated whether high NO concentrations could be responsible for the decrease in NOS neurones. Myenteric neurone cultures, prepared from guinea-pig small intestine, were incubated with NO donors [sodium nitroprusside (SNP) and 3-morpholinosydnonimine (SIN-1)]. After fixation, NOS neurones were identified by NADPH diaphorase staining and neurone-specific enolase (NSE)-positive neuronal content was assessed with an enzyme-linked immunosorbent assay (ELISA)-based method. Twenty-four hours incubation with SIN-1 (10(-3) mol L(-1)) or SNP (10(-4) mol L(-1) or higher) reduced the number of NADPH diaphorase-positive neurones. SNP incubation did not affect the NSE-positive neuronal content. Shorter incubations (SNP: 4 and 12 h) had no significant effect. The SNP-induced reduction was reversed by glutathione (GSH), but not by NO- or O-scavengers, whereas GSH depletion enhanced the decrease. The NO-dependent guanylate cyclase-blocker 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) did not affect the SNP effect. This reduction can be explained by either specific apoptosis of NOS neurones or downregulation of NOS activity. However, TdT-mediated X-dUTP nick end labelling (TUNEL stainings argue in favour of the latter. In conclusion, the NO donor SNP decreases the number of NOS-expressing myenteric neurones time and concentration dependently, without affecting the amount of neuronal material. Glutathione plays an important protective role.     

Indiscriminate loss of myenteric neurones in the TNBS-inflamed guinea-pig distal colon

This investigation was conducted to establish whether guinea-pig trinitrobenzene sulfonic acid (TNBS)-colitis was associated with a change in the number of neurones of the myenteric plexus, and, if so, whether select subpopulations of neurones were affected. Total neurones were quantified with human (Hu) antiserum, and subpopulations were evaluated with antisera directed against choline acetyltransferase, nitric oxide synthase, calretinin, neuronal nuclear protein or vasoactive intestinal peptide (VIP). Colitis was associated with a loss of 20% of the myenteric neurones, most of which occurred during the first 12 h past-TNBS administration. During this period, myenteric ganglia were infiltrated with neutrophils while lymphocytes appeared at a later time-point. The neuronal loss persisted at a 56-day time-point, when inflammation had resolved. The decrease in myenteric neurones was not associated with a decrease in any given subpopulation of neurones, but the proportion of VIP-immunoreactive neurones increased 6 days following TNBS administration and returned to the control range at the 56 days. These findings indicate that there is an indiscriminant loss of myenteric neurones that occurs during the onset of TNBS-colitis, and the loss of neurones may be associated with the appearance of neutrophils in the region.     

The relationship between inflammation‐induced neuronal excitability and disrupted motor activity in the guinea pig distal colon

Background Colitis is associated with increased excitability of afterhyperpolarization neurons (AH neurons) and facilitated synaptic transmission in the myenteric plexus. These changes are accompanied by disrupted propulsive motility, particularly in ulcerated regions. This study examined the relationship between myenteric AH neuronal hyperexcitability and disrupted propulsive motility. Methods The voltage‐activated Na⁺ channel opener veratridine, the intermediate conductance Ca²⁺‐activated K⁺ channel inhibitor TRAM‐34 and the 5‐HT₄ receptor agonist tegaserod were used to evaluate the effects of neuronal hyperexcitability and synaptic facilitation on propulsive motility in normal guinea pig distal colon. Because trinitrobenzene sulfonic acid (TNBS)‐colitis‐induced hyperexcitability of myenteric afferent neurons involves increases in hyperpolarization‐activated, cyclic nucleotide‐gated (HCN) channel activity, the HCN channel inhibitors Cs⁺ and ZD7288 were used to suppress AH neuronal activity in TNBS‐colitis. Key Results In non‐inflamed preparations, veratridine halted propulsive motility (P < 0.001). The rate of propulsive motor activity was significantly reduced following addition of TRAM‐34 and tegaserod (P < 0.001). In TNBS‐inflamed preparations, in which motility was temporarily halted or obstructed at sites of ulceration, both Cs⁺ and ZD7288 normalized motility through the inflamed regions. Immunohistochemistry studies demonstrated that the proportion of AH neurons in the myenteric plexus was unchanged in ulcerated regions, but there was a 10% reduction in total number of neurons per ganglion. Conclusions and Inferences These findings support the concept that inflammation‐induced neuroplasticity in myenteric neurons, involving changes in ion channel activity that lead to enhanced AH neuronal excitability, can contribute to impaired propulsive colonic motility.     

Prolonged IL‐1β exposure alters neurotransmitter and electrically induced Ca2+ responses in the myenteric plexus

Background Infection and inflammatory diseases of the gut results in profound changes of intestinal motor function. Acute administration of the pro‐inflammatory cytokine interleukin‐1β (IL‐1β) was shown to have excitatory and neuromodulatory roles in the myenteric plexus. Here we aimed to study the effect of prolonged IL‐1β incubation on the response of myenteric neurones to different stimuli. Methods Longitudinal muscle myenteric plexus preparations (LMMP’s) of the guinea pig jejunum were incubated for 24 h in medium with or without IL‐1β. After loading with Fluo‐4, calcium imaging was used to visualize activation of neurones. The response to application of serotonin (5‐HT), substance P (SP) and ATP or to electrical fibre tract stimulation (eFTS) was tested. Expression of nNOS, HuD, calbindin and calretinin was compared by immunohistochemistry. Key Results IL‐1β concentration‐dependently influenced the neuronal responsiveness and duration of the [Ca²⁺]_i rises to 5‐HT and ATP, while it also affected the Ca²⁺‐transient amplitudes induced by 5‐HT, ATP and SP. Ca²⁺‐transients in response to eFTS were observed in significantly more neurones per ganglion after IL‐1β (10^?10 and 10^?11 mol L^?1). Peak [Ca²⁺]_i rise after eFTS was concentration‐dependently decreased by IL‐1β. The duration of the [Ca²⁺]_i rise after eFTS was prolonged after IL‐1β 10^?12 mol L^?1. IL‐1β (10^?9 mol L^?1) incubation did not affect the number of nNOS, calretinin and calbindin expressing neurones, nor did it induce neuronal loss (HuD). Conclusions & Inferences In this study, IL‐1β differentially modulates the neuronal response to eFTS and neurotransmitter application in the myenteric plexus of guinea pigs. This cytokine could be implicated in the motility disturbances observed during gastrointestinal inflammation.     

The effects of glucagon‐like peptide 2 on enteric neurons in intestinal inflammation

Background Intestinal inflammation alters the structure and function of the enteric nervous system (ENS). Glucagon‐like peptide 2 (GLP‐2) reduces intestinal inflammation and has trophic effects on isolated neurons. This study examined the effects of GLP‐2 treatment on the submucosal plexus of rat colon in the trinitrobenzene sulfonic acid (TNBS) model of colitis. Methods After administration of TNBS or saline/ethanol for controls, animals were allocated to treatment with GLP‐2 (50 μg kg^?1day^?1, s.c.) or sham injection of vehicle, twice daily. Animals were monitored, following clinical parameters, and killed on day 5. The number of neuronal cell bodies per ganglion was quantified using immunohistochemistry on submucosal whole mount preparations, with further characterization of specific subpopulations using antibodies against vasoactive intestinal polypeptide (VIP), neuronal nitric oxide synthase (nNOS), and enteric glial cells with glial fibrillary acid protein and S100. Key Results Glucagon‐like peptide 2 treatment was associated with a significant amelioration of weight loss, and reduced neutrophil infiltration and microscopic colitis scores in the TNBS animals. Inflammation resulted in a loss of enteric neurons in submucosal ganglia; GLP‐2 treatment restored the enteric neuronal populations to normal. In control, non‐inflamed animals, GLP‐2 treatment increased the number of VIP expressing neurons per ganglion; in TNBS‐treated animals, GLP‐2 prevented an inflammation‐induced reduction in the numbers of VIP expressing neurons per ganglion. Glucagon‐like peptide 2 did not change the numbers of nNOS neurons or enteric glial cells in either the control, or inflamed state. Conclusions & Inferences These findings show that GLP‐2 increased the number of VIP expressing neurons in normal animals, and prevents the inflammation‐induced loss of neurons in the colonic submucosal ganglia, with an increase in the proportion of VIP expressing neurons. They suggest that GLP‐2 may have a role in protecting or regulating the circuitry of the ENS under basal and inflamed states.     

Changes in nitrergic innervation of defunctionalized rat colon after diversion colostomy

Abstract  After 45 days of complete diversion colostomy in male Wistar rats, morphometry of soma and nuclei of NADPH diaphorase positive cells of the myenteric plexus was evaluated. There was a significant ( P  < 0.0001) diminution in the area, perimeter and volume-weighted mean volume of soma and nuclei of nitrergic myenteric neurones in the defunctionalized colon. In addition, there was a significant reduction in the neuronal density of the myenteric neurones, and increased distance between the ganglia. In addition, there was myenteric glial atrophy. Atrophy of colonic myenteric neurones was accompanied by significant reduction ( P  < 0.001) in the volume fraction of the muscularis externa, the prime targets of these neurones. The disturbances in the microecology of the colon may jeopardize the finely orchestrated functioning of the components of the Enteric nervous system (ENS) leading to colonic dysfunction. Our observations, by extrapolation, may explain the bowel dysmotility in humans after restoration of colonic continuity after colostomy.     

Impaired intestinal gas propulsion in manometrically proven dysmotility and in irritable bowel syndrome

Background Intestinal manometry is the current gold standard for diagnosing small bowel dysmotility; however, the functional significance of abnormal manometry is unknown. Our aim was to determine whether, and to what extent, intestinal gas propulsion is impaired in patients with manometrically proven dysmotility compared with healthy controls and patients with IBS. Methods Clearance and tolerance of a jejunal gas load (12 mL min^?1 for 2 h) were measured in 15 patients with severe abdominal symptoms and intestinal dysmotility evidenced by manometry, 15 patients with IBS and 15 healthy subjects. Thereafter, the effect of neostigmine (0.5 mg i.v. bolus) vs placebo (i.v. saline) was tested in six dysmotility patients. Key Results After 2‐h gas infusion, patients with dysmotility developed significantly more gas retention (717 ± 91 mL) than IBS patients (372 ± 82 mL; P = 0.0037) and healthy subjects (17 ± 67 mL; P < 0.0001 vs dysmotility; P = 0.0060 vs IBS). Despite the greater retention in dysmotility patients, abdominal perception (2.5 ± 0.6 score) and distension (7 ± 2 mm girth increment) were similar to IBS (3.9 ± 0.6 score and 7 ± 2 mm, respectively). In dysmotility patients, neostigmine produced immediate clearance of gas, and by 30 min had reduced gas retention (by ?552 ± 182 vs 72 ± 58 mL after saline; P = 0.008), abdominal symptoms (by ?0.8 ± 0.3 score vs 0.3 ± 0.2 after saline; P = 0.019) and distension (girth change ?5 ± 1 mm; P = 0.003 vs?2 ± 2 mm after saline). Conclusion & Inferences Patients with manometric dysmotility have markedly impaired intestinal gas propulsion. In IBS patients, impaired gas propulsion is less pronounced but associated with concomitant sensory dysfunction and poor tolerance of gas retention.     

Role of nitric oxide in norepinephrine release from myenteric plexus in vitro and in Trichinella spiralis-infected rats

Nitric oxide (NO) has been implicated as modulator of neural function and inflammatory mediator. Previously, we have demonstrated suppression of norepinephrine (NE) release from myenteric nerves following Trichinella spiralis infection implicating interleukin-1β (IL-1β) as a mediator of these changes. In the present study, we have examined the role of NO in NE release from the myenteric plexus and in the suppression of NE release induced by IL-1β in vitro, and we have determined whether NO is involved in the suppression of NE release from the myenteric plexus observed in T. spiralis-infected rats. Electrically evoked NE release from jejunal longitudinal muscle–myenteric plexus preparations (LMMP) was measured following (a) in vitro exposure of the tissue to the NO donor 3-morpholinosydnonimine (SIN-1), L-arginine, or IL-1β, in the presence or absence of NOS inhibitors, and (b) in vivo treatment of control or T. spiralis-infected rats with N⁶-nitro-L-arginine-methyl-ester (L-NAME), N^G-nitro-D-arginine-methyl-ester (D-NAME) or vehicle for 6 days. In vitro inhibition of NO synthesis had no effect on NE release from the myenteric plexus. Treatment with SIN-1 or L-arginine suppressed NE release in a manner similar to that observed with IL-1β. Moreover, the effect of IL-1β was attenuated by L-NAME. In contrast, treatment of T. spiralis-infected rats with L-NAME had no effect on the suppression of NE release. These results indicate that in the absence of inflammation, the myenteric plexus can generate sufficient NO to inhibit NE release and that NO mediates the action of IL-1β on NE release in vitro. However, we have no evidence for the involvement of NO in the suppression of NE release in nematode-infected rats.     

Distinctive motor responses to human acute salmonellosis in the jejunum and ileum

Given the differences that normally exist in jejunal and Heal motility patterns, we wished to determine whether these regions respond differently to acute enteric infections. In 10 patients with acute gastroenteritis induced by Salmonella infection and 12 healthy individuals jejunal and Heal motility was recorded at eight equidistant sites by a manometric system for 6 h during fasting. All were healthy individuals, but only three of 10 patients exhibited the cyclic inter digestive motor complex; 82 ± 9 min duration in healthy individuals (mean ± SE). In the jejenum, patients exhibited short bursts of intense activity (6.3 ± 1.6 bursts/subject in patients vs. 1.8 ± 0.5 in controls; P < 0.05); burst activity was scarce in the ileum. In contrast to healthy subjects, patients exhibited prolonged periods (64 ± 3 min duration) of Heal motor quiescence, that accounted for 32 ± 11% of recording time; such silent periods were not observed in the jejunum. Prolonged propagated ileal contractions were observed only in two healthy subjects, but in seven out of 10 patients. These data indicate that acute Salmonella infection magnifies the motor differences between the jejunum and the ileum; both regions generate aberrant and markedly different dysmotility patterns.     

Prokineticin 1 inhibits spontaneous giant contractions in the murine proximal colon through nitric oxide release

Prokineticins are novel peptides with reported effects on gastrointestinal contractility. Prokineticin actions are mediated by distinct prokineticin receptors (PKR1 and PKR2). This study investigated the role of prokineticin 1 in colonic contractility as well as sites of expression of its receptor in the mouse proximal colon by immunohistochemistry and confocal microscopy. Prokineticin 1 suppressed giant contractions in circular muscle. The inhibitory effect of prokineticin 1 on giant contractions was blocked by the nitric oxide synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME). In vitro, prokineticin 1 stimulated nitric oxide release from longitudinal muscle-myenteric plexus cultures. This effect was blocked by L-NAME. PKR1 is expressed on myenteric plexus neurons and colocalizes with a small subset of nNOS expressing neurons. This study suggests that PKR1 mediates an inhibitory effect in vitro, most likely through direct or indirect stimulation of nitric oxide release. PKR1 and its natural ligand, prokineticin 1 may be important for modulation of colonic motility.     

IL-1β and IL-6 excite neurones and suppress cholinergic neurotransmission in the myenteric plexus of the guinea pig

The effects of the inflammatory mediators interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) on myenteric neurones were investigated by intracellular recordings in a conventional myenteric plexus preparation of guinea pig ileum. Micropressure ejection of IL-1beta and IL-6 (10-7 mol L-1) both caused an excitatory effect in, respectively, 19% (13/70) and 7% (5/70) of the myenteric neurones. The IL-1beta-induced depolarizations were inhibited by superfusion of the IL-1beta receptor antagonist. The responses seen were tetrodotoxin-resistant, indicating a direct neuronal effect. Responses to both cytokines were seen in nitric oxide synthase-immunoreactive as well as choline acetyltransferase-immunoreactive neurones. In addition, both IL-1beta and IL-6 reversibly caused a presynaptic inhibition of acetylcholine release from cholinergic nerve terminals. Both cytokines had no effect on the slow excitatory postsynaptic potentials. Therefore, we can conclude that the inflammatory mediators IL-1beta and IL-6 can act as excitatory neuromodulators of gastrointestinal motility through direct excitatory actions on a subset of myenteric neurones and through the presynaptic inhibition of acetylcholine release.     

Effect of 2,4,6-trinitrobenzenesulphonic acid (TNBS)-induced ileitis on the motor function of non-inflamed rat gastric fundus.

During intestinal inflammation, motility disturbances are not restricted to inflamed regions, but may also occur in remote non-inflamed 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 inflammation was induced by intraluminal installation of 2,4,6-trinitrobenzenesulphonic acid (TNBS) into the ileum. Inflammation 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 inflammation (36 h), the non-inflamed 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-inflamed gastric fundus. This phenomenon may be mediated by intrinsic connections within the enteric nervous system.     

Role of capsaicin-sensitive afferent nerves in different models of gastric inflammation in rats

Capsaicin-sensitive afferent nerves are described as being protective against gastric inflammation; their destruction leads to an exacerbation of inflammatory processes. However, these nerves have been shown to exert a pro-inflammatory action on stress-induced gastritis in rats. Our study aimed to investigate the role of capsaicin-sensitive afferent nerves in different experimental models of gastritis in rats. Functional ablation of sensory nerves was achieved by systemic capsaicin treatment (100 mg/kg). Gastritis was induced by mild (iodoacetamide, diquat, surgical duodeno-gastric reflux [DGR]) and strong (70% ethanol, indomethacin) inflammatory agents. Antagonists of the CGRP1 and NK1 receptors, hCGRP8-37 and SR140333, were administered in rats treated with iodoacetamide and ethanol. Macroscopic damage scores (MDS), myeloperoxidase (MPO) activity and malondialdehyde (MDA) concentration were evaluated after sacrifice. Macroscopic lesions appeared only in ethanol and indomethacin gastritis and were enhanced by capsaicin treatment. Gastric MPO activity was significantly increased by all agents compared to controls. Capsaicin treatment did not have any effect on MPO activity in indomethacin-treated rats or in rats submitted to surgery for duodeno-gastric reflux. However, it abolished the increase in MPO induced by iodoacetamide and diquat, and significantly enhanced that induced by ethanol. hCGRP8-37 and SR140333 abolished the increase in MPO activity and MDA concentration in iodoacetamide treated rats. In ethanol-treated rats, SR140333 diminished MPO activity. These results indicate that, depending upon the nature and duration of the experimental inflammation, capsaicin-sensitive afferent nerves may act differently to control gastric inflammatory processes, suggesting the involvement of a neurogenic component in some forms of gastric inflammation.     

N‐Methyl‐d‐aspartate receptor antagonism decreases motility and inflammatory activation in the early phase of acute experimental colitis in the rat

Background Inflammatory bowel diseases are accompanied by severe motility disorders. The aim of our study was to investigate whether the blockade of peripheral N‐methyl‐D‐aspartate (NMDA)‐sensitive glutamate receptors (NMDA‐Rs) alters motility changes in chemically induced acute colitis and how this modulation is accomplished. Methods The inflammatory and motility changes in 2,4,6‐trinitrobenzenesulfonic acid (TNBS)‐induced colitis were studied in anaesthetized Wistar rats following treatment with the natural NMDA‐R antagonist kynurenic acid (KynA) or SZR‐72, a blood‐brain barrier‐permeable synthetic KynA analogue. The macrohaemodynamics, serosal microcirculation (visualized by intravital videomicroscopy), plasma levels of tumour necrosis factor alpha (TNF‐α), inflammatory enzyme activities (xanthine oxidoreductase (XOR), myeloperoxidase (MPO) and nitric oxide synthase (NOS)), and colonic motility (with a strain‐gauge technique) were evaluated 17 h after colitis induction and compared with the control conditions. Key Results The TNBS enema induced a systemic hyperdynamic circulatory reaction, increased the serosal capillary blood flow, significantly elevated the mucosal XOR, MPO and NOS activities and augmented the colonic motility relative to the controls. The NMDA‐R antagonist treatment with KynA or SZR‐72 significantly reduced the XOR, NOS and MPO activities, decreased the motility and increased the tone of the colon. Conclusions & Inferences These data demonstrate a potential modulatory mechanism of NMDA‐R in altered colonic motility in TNBS colitis. Inhibition of the enteric NMDA‐Rs may provide a therapeutic option via which to influence intestinal hypermotility, microcirculatory changes and inflammatory activation simultaneously.     

Enhanced intestinal motor response to cholecystokinin in post-Nippostrongylus brasiliensis-infected rats: modulation by CCK receptors and the vagus nerve

The jejunal inflammation induced in rats by the nematode Nippostrongylus brasiliensis is followed by intestinal neuroimmune alterations including mast cell hyperplasia and nerve remodelling. On the other hand, cholecystokinin (CCK) plays a pivotal role in the regulation of intestinal motility. The aim of this study was to determine whether the intestinal motor response to CCK is altered 30 days after infection by N. brasiliensis. Thus, CCK-8 (50 microg kg(-1) intraperitoneally) disrupted the pattern of jejunal migrating myoelectric complexes for a longer time in postinfected rats (95.5 +/- 3.5 min) than in controls (48.1 +/- 5.1 min). This enhanced jejunal response was also found after oral administration of the potent releaser of endogenous CCK, soybean trypsin inhibitor. In contrast, no alteration of the inhibition of colonic motility by CCK administration was observed. The increased responsiveness of jejunal motility to CCK persisted after mast cell stabilisation or depletion but was prevented by atropine, devazepide and L-365260 (CCK-A and CCK-B receptor antagonists, respectively) and vagotomy. These results indicate that neuroimmune alterations after N. brasiliensis infection lead to an increased intestinal motility response to CCK that involves a cholinergic mediation, a vagal pathway and alterations in intestinal CCK-A and CCK-B receptors.