Prostaglandin EP receptor subtypes have distinctive effects on jejunal afferent sensitivity in the rat

The Fecal Microbiota Transplantation: A Remarkable Clinical Therapy for Slow Transit Constipation in Future

Slow transit constipation is a common condition that would be difficult to treat in clinical practice with a widespread incidence in the population. Pharmacotherapy and surgery are common treatment modalities. However, the clinical effect is limited, and patients still suffer from it. As the researchers strived in this field for decades, the profound relationship between slow transit constipation and fecal microbiota transplantation has comprehensively been sustained. It is very pivotal to maintain intestinal homeostasis, the structure function and metabolic function of symbiotic bacteria, which can inhibit the engraftment of intestinal pathogens. This mini review explains the treatment effects and possible mechanisms of the fecal microbiota transplantation in treating slow transit constipation. Simultaneously, it is found that there is significant improvement in the disease by adjusting the intestinal microbes like fecal microbiota transplantation. Fecal microbiota transplantation has efficient therapeutic effects in slow transit constipation compared with traditional therapies.

Prostaglandin E2 stimulates anion and fluid secretion triggered by lipopolysaccharide in rat vaginal epithelium

Prostaglandin E2 (PGE2) is a principal lipid mediator mediating various biological processes including immune responses and fluid secretion. As the first line of host defense against infection, vaginal epithelium plays orchestrated roles in vaginal innate immunity. However, the effect of PGE2 triggered by pro-inflammatory stimuli on vaginal epithelium remains elusive. This study aimed to investigate the regulatory role of PGE2 on vaginal epithelium after lipopolysaccharide (LPS) stimulation. RT-PCR and western blot analysis revealed that E-prostanoid (EP) receptors EP2 and EP4 were expressed in rat vagina. Basolateral application of PGE2 induced anion secretion mediated by cystic fibrosis transmembrane conductance regulator (CFTR) via EP-adenylate cyclase-cAMP signaling pathway in rat vaginal epithelial cells. The in vivo study showed that PGE2 promoted fluid secretion in rat vagina. Moreover, LPS stimulation facilitated cyclooxygenase-dependent PGE2 synthesis and vaginal fluid secretion in vivo. Conclusively, LPS stimulation triggered epithelium-derived PGE2 production in vaginal epithelium, leading to CFTR-mediated anion secretion and luminal flushing. This study provides valuable insights into the physiological role of PGE2 during vaginal bacterial infection.

Prostaglandin E2 receptors and their role in gastrointestinal motility - Potential therapeutic targets

Prostaglandin E₂ (PGE₂) is found throughout the gastrointestinal tract in a diverse variety of functions and roles. The recent discovery of four PGE₂ receptor subtypes in intestinal muscle layers as well as in the enteric plexus has led to much interest in the study of their roles in gut motility. Gut dysmotility has been implicated in functional disease processes including irritable bowel syndrome (IBS) and slow transit constipation, and lubiprostone, a PGE₂ derivative, has recently been licensed to treat both conditions. The diversity of actions of PGE₂ in the intestinal tract is attributed to its differing effects on its downstream receptor types, as well as their varied distribution in the gut, in both health and disease. This review aims to identify the role and distribution of PGE₂ receptors in the intestinal tract, and aims to elucidate their distinct role in gut motor function, with a specific focus on functional intestinal pathologies.

AH6809 decreases production of inflammatory mediators by PGE2 - EP2 - cAMP signaling pathway in an experimentally induced pure cerebral concussion in rats

Increasing evidence suggests that PGE₂ metabolic pathway is involved in pathological changes of the secondary brain injury after traumatic brain injury. However, the underlying mechanisms, in particular, the correlation between various key enzymes and the brain injury, has remained to be fully explored. More specifically, it remains to be ascertained whether AH6809 (an EP2 receptor antagonist) would interfere with the downstream of the PGE₂, regulate the inflammatory mediators and improve neuronal damage in the hippocampus by PGE₂ - EP2 - cAMP signaling pathway. The expression and pathological changes of cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), microsomal prostaglandin-E synthase-1 (mPGES-1), E-prostanoid receptor 2 (EP2), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and inducible nitricoxide synthase (iNOS) in the CA1 area of hippocampus were evaluated by immunohistochemistry, Western blot and RT-PCR after pure cerebral concussion (PCC) induced by a metal pendulum closed brain injury in rats followed by AH6809 treatment. The morphology and number of neurons in CA1 region were analyzed by cresyl violet staining. The concentration of prostaglandin E₂ (PGE₂) and cyclic adenosine monophosphate (cAMP) was assayed by ELISA. Many neurons in hippocampal CA1 area appeared to undergo necrosis and the number of neurons was concomitantly reduced after PCC injury. With the passage of time, the protein and mRNA expression of various key enzymes including COX-1, COX-2 and mPGES-1, EP2 receptor, and inflammatory mediators including TNF-α, IL-1β and iNOS was increased; meanwhile, the concentration of PGE₂ and cAMP was enhanced. After PCC injury given AH6809 intervention, injury of neurons in hippocampal CA1 area was attenuated. The protein and mRNA expression of COX-1, COX-2, mPGES-1, EP2, TNF-α, IL-1β and iNOS was decreased, this was coupled with reduction of PGE₂ and cAMP. The results suggest that PGE₂ metabolic pathway is involved in secondary pathological changes of PCC. AH6809 improves the recovery of injured neurons in the hippocampal CA1 area and downregulates the inflammatory mediators by PGE₂ - EP2 - cAMP signaling pathway.

Modulation of intestinal afferent nerve sensitivity to inflammatory mediators following systemic endotoxin in mice

BACKGROUND

Endotoxin exposure may be followed by visceral hypersensitvity but potential mechanisms are not fully explored. We aimed to test the hypothesis that mast cells and the cyclooxygenase pathway (COX) mediate modulation of afferent nerve sensitivity following systemic endotoxin.

METHODS

C57Bl6 mice received endotoxin injection i.p. to induce systemic inflammation. Control animals received normal saline. Extracellular multi-unit afferent nerve discharge was recorded from jejunal mesenteric nerves in vitro. Afferent nerve response to 5-hydroxytryptamine (5-HT, 250 μmol/L), bradykinin (BK, 0.5 μmol/L), and to mechanical ramp distension of the intestinal lumen from 0 to 60 cmH2O were recorded 2 h following endotoxin administration.

KEY RESULTS

Following endotoxin administration peak afferent discharge to 5-HT and BK was increased compared to controls (p < 0.05). Pre-perfusion with the mast cell stabilizer Doxantrazole (10(-4) M), or the cyclooxygenase inhibitor Naproxen inhibited the increased response to 5-HT and BK (p < 0.05 vs endotoxin pretreatment). Mechanosensitivity during luminal ramp distension from 10 to 60 cmH2O was increased following endotoxin pretreatment compared to controls (p < 0.05). This increase in sensitivity following endotoxin was no longer observed after Doxantrazole or Naproxen administration for pressures from 10 to 30 cmH2O (p < 0.05). Selective COX-2 inhibition by NS398 (10 μM) but not COX-1 inhibition by SC560 (300 μM) reduced increased afferent discharge in endotoxin pretreated animals to 5-HT, BK and mechanical ramp distension from 10 to 40 cmH2O (all p < 0.05).

CONCLUSIONS & INFERENCES

Systemic endotoxin sensitizes mesenteric afferent nerve fibers to 5-HT, BK and mechanical stimuli. The underlying mechanism responsible for this sensitization seems to involve mast cells and the COX-2 pathway.

Constitutive cyclo-oxygenase-2 does not contribute to the development of human visceral pain hypersensitivity

BACKGROUND AND AIMS

Central sensitisation (CS), contributes to the development and maintenance of gastrointestinal pain hypersensitivity. Constitutive cyclo-oxygenase-2 (COX-2) contributes to central sensitisation in somatic pain hypersensitivity but its role in mediating visceral pain hypersensitivity is unknown. We therefore conducted a study to determine if COX-2 inhibition with Valdecoxib attenuates the development or early maintenance of CS in a validated human oesophageal pain hypersensitivity model.

METHODS

Healthy volunteers were studied in two randomised, double blind, crossover studies in which pain thresholds (PT) to electrical stimulation were assessed in the proximal oesophagus, chest wall and foot, prior to and following a distal oesophageal acid infusion. Protocol 1: Valdecoxib, (40 mg) or matching placebo was given orally for 4 days prior to oesophageal acid infusion. Protocol 2: IV Parecoxib (40 mg) or saline was given 120 min after oesophageal acid infusion.

RESULTS

Valdecoxib did not prevent the induction of secondary allodynia in the proximal oesophagus nor did it attenuate it following its establishment. Chest wall PT fell following oesophageal acid but foot PT remained unchanged; highlighting the development viscero-somatic convergence due to CS. Valdecoxib had no analgesic or anti-hyperalgesic effect on chest wall or foot PT.

CONCLUSIONS

Neither the induction nor initial maintenance of acid induced oesophageal pain hypersensitivity is prevented by Valdecoxib, suggesting that constitutive spinal COX-2 does not contribute to the development or early maintenance of acute visceral central sensitisation.

Mast cells drive mesenteric afferent signalling during acute intestinal ischaemia

Acute intestinal ischaemia stimulates visceral afferent nerves but the mechanisms responsible for this excitation are not fully understood. Mast cells may participate in this process as they are known to signal to mesenteric afferents during intestinal anaphylaxis and contribute to early inflammation and neuronal damage in response to cerebral ischaemia. We therefore hypothesised that mast cells are early responders to acute intestinal ischaemia and their activation initiates rapid signalling to the CNS via the excitation of mesenteric afferents. Primary afferent firing was recorded from a mesenteric nerve bundle supplying a segment of jejunum in anaesthetized adult rats. Acute focal ischaemia was produced by clamping theme senteric vessels for 8 min, and reperfusion followed removal of the vessel clip. Two episodes of ischaemia–reperfusion (I–R) separated by a 30 min interval were performed. Drugs or their vehicles were administered 10 min before the 2nd I–R episode. Ischaemia caused a reproducible, intense and biphasic afferent firing that was temporally dissociated from the concomitantly triggered complex pattern of intestinal motor activity. The L-type calcium channel blocker, nifedipine, significantly attenuated this afferent firing by a mechanism independent of its action on intestinal tone. Ischaemia-induced afferent firing was also abrogated by the mast cell stabilizer, doxantrazole, and the H1 histamine receptor antagonist, pyrilamine. In contrast, the nicotinic receptor antagonist, hexamethonium, and the N-type calcium channel toxin, ω-conotoxin GVIA, each reduced the ischaemia-evoked motor inhibition but not the concurrent afferent discharge. Similarly, the cyclooxygenase inhibitor, naproxen, had no effect on the ischaemic afferent response but reduced the intestinal tone shortly from the onset of ischaemia to the early period of reperfusion. These data support a critical role for mast cell-derived histamine in the direct chemoexcitation of mesenteric afferents during acute intestinal ischaemia, whereas enteric reflex mechanisms and cyclooxygenase products contribute primarily to ischaemia-induced changes in intestinal motility. Therefore, targeting mast cells may provide benefits in patients with abdominal pain resulting from an ischaemic insult to the gastrointestinal tract.

Differential afferent sensitivity to mucosal lipopolysaccharide from Salmonella typhimurium and Escherichia coli in the rat jejunum

Postinfectious irritable bowel syndrome may develop subsequent to acute bacterial enteritis. We therefore hypothesized that intestinal afferents may develop hypersensitivity upon exposure to luminal lipopolysaccharide (LPS) from pathogens but not from commensal bacteria and that this may be prostaglandin mediated. Extracellular recordings of jejunal afferents were obtained in vivo from male Wistar rats (n = 5 per group; 300-400 g). Lipopolysaccharide from Escherichia coli (E-LPS), Salmonella typhimurium (S-LPS) or vehicle were infused into the intestinal lumen at 5 mg mL(-1). The selective 5-HT(3)-receptor agonist 2-methyl-5-HT (2m5-HT, 15 microgkg(-1), i.v.) was administered at 15-min intervals before and up to 2 h after S-LPS administration. Intraluminal E-LPS had no effect on mesenteric afferent nerve discharge at baseline. By contrast, afferent discharge increased from 21.7 +/- 0.3 impsec(-1) to 28.8 +/- 3.4 impsec(-1) 40 min after S-LPS administration (mean +/- SEM; P < 0.05) and reached 38.8 +/- 4.1 impsec(-1) after 2 h (P < 0.05). The afferent response to 2m5-HT was enhanced 30 min following S-LPS by 30.9 +/- 3.9% (P < 0.05) and remained elevated thereafter. The increase in baseline discharge and sensitivity to 2m5-HT following S-LPS was prevented by pretreatment with naproxen (COX inhibitor, 10 mgkg(-1) i.v.) or AH-6809 (EP1/EP2 receptor antagonist, 1 mg kg(-1)). Intestinal afferents do not alter their discharge rate to LPS from E. coli but to LPS from the pathogenic bacterium S. typhimurium. The latter response entails afferent sensitisation to 2m5-HT that depends on prostanoid release. This acute sensitisation may prime the intestinal afferent innervation for a later development of persistent hypersensitivity.

Mechanotransduction and chemosensitivity of two major classes of bladder afferents with endings in the vicinity to the urothelium

The guinea pig bladder is innervated by at least five distinct major classes of extrinsic sensory neurons. In this study, we have examined the mechanisms of mechanotransduction and chemosensitivity of two classes of bladder afferents that have their endings in the vicinity of the urothelium: stretch-sensitive muscle-mucosal mechanoreceptors and stretch-insensitive, mucosal high-responding afferents. The non-selective P2 purinoreceptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid did not affect stretch- or stroking-induced firing of these afferents but significantly reduced the excitatory action of alpha,beta-methylene ATP. Blocking synaptic transmission in Ca(2+)-free solution did not affect stretch-evoked firing but slightly reduced stretch-induced tension responses. Stroking-induced firing of both classes of afferents was also not affected in Ca(2+)-free solution. Of blockers of mechano-gated channels, benzamil (100 microM), but not amiloride (100 microM), Gd(3+) (100 microM) or SKF 96365 (50 microM), inhibited stretch- and stroking-induced firing. Serotonin (100 microM) applied directly onto receptive fields predominantly activated muscle-mucosal afferents. Muscarine (100 microM) and substance P (100 microM) in 24% and 36% cases activated only mucosal high-responding units. Bradykinin (10 microM), but not prostaglandin E2 (10 microM), excites predominantly mucosal units. High (80 mM) K(+) solution activated both afferent classes, but responses of mucosal units were 4 times greater. In contrast to muscle-mucosal units, most mucosal high-responding units were activated by hot Krebs solution (45-46 degrees C), low pH (pH 4) and capsaicin (3 microm). TRPV1 antagonist, capsazepine (10 microM) was without effect on mechanotransduction by mucosal high-responding afferents. The results show that mechanotransduction of these two types of afferents are not dependant upon Ca(2+)-dependent exocytotic release of mediators, or ATP, and it is likely that benzamil-sensitive stretch-activated ion channels on their endings are involved in direct mechanotransduction. The chemosensitivity to agonists and noxious stimuli differs significantly between these two major classes of bladder afferents that reflects their different physiological and pathophysiological roles in the bladder.

Neuronal activation in the nucleus of the solitary tract following jejunal lipopolysaccharide in the rat

INTRODUCTION

Inflammation during systemic lipopolysaccharide (LPS) seems to be modulated by the CNS via afferent and efferent vagal pathways. We hypothesized that similar to systemic inflammation, local LPS in the gut lumen may also activate central neurons and aimed to identify potential molecular mechanisms.

METHODS

Male Wistar rats were equipped with an exteriorized canula in the proximal jejunum. LPS or vehicle were administered into the jejunum (10 mg ml(-1)). For further study of molecular mechanisms, LPS or vehicle were administered systemically (1 mg kg(-1)). Brain stem activation was quantified by Fos-immunohistochemistry in the vagal nucleus of the solitary tract (NTS) and the Area postrema which is exposed to systemic circulation. Serum LPS concentrations were also determined.

RESULTS

Jejunal LPS exposure entailed 91+/-12 (n=7) Fos-positive neurons in the NTS compared to 39+/-9 in controls (n=6; p<0.01), while serum LPS concentrations and Fos-positive neurons in the Area postrema were not different. Systemic LPS triggered 150+/-25 (n=6) and vehicle 52+/-6 Fos-positive neurons (n=7; p<0.01). The Fos count after systemic LPS was reduced to 99+/-30 following pretreatment with the cyclooxygenase inhibitor Naproxen (10 mg kg(-1); p>0.05 versus vehicle controls) and increased to 242+/-66 following the iNOS-inhibitor Aminoguanidine (15 mg kg(-1); p<0.01). In the Area postrema, 97+/-17 (n=6) neurons were counted in animals pretreated with systemic LPS compared to 14+/-4 in controls (n=7, p<0.001).

CONCLUSIONS

Central neuronal activation following inflammation after systemic LPS is modulated by cyclooxygenase and NO pathways. Local exposure to bacterial LPS in the gut lumen activates the NTS which may set the stage for efferent vagal modulation of intestinal inflammation.

Afferent nerve sensitivity is decreased by an iNOS-dependent mechanism during indomethacin-induced inflammation in the murine jejunum in vitro

Evidence exists that visceral afferent sensitivity is subject to regulatory mechanisms. We hypothesized that afferent sensitivity is decreased in the small intestine during intestinal inflammation by an inducible nitric oxide synthase (iNOS)-dependent mechanism. C57BL/6 mice were injected twice with vehicle or 60 mg kg(-1) indomethacin subcutaneously to induce intestinal inflammation. Afferent sensitivity was recorded on day 3 from a 2-cm segment of jejunum in vitro by extracellular multi-unit afferent recordings from the mesenteric nerve bundle. In subgroups (n = 6), iNOS was inhibited selectively by L-N6-(1-iminoethyl)-lysine (L-NIL) given either chronically from day 1-3 (3 mg kg(-1) twice daily i.p.) or acutely into the organ bath (30 micromol L(-1)). The indomethacin-induced increase of macroscopic and microscopic scores of intestinal inflammation (both P < 0.05) were unchanged after pretreatment with L-NIL. Peak afferent firing following bradykinin (0.5 micromol L(-1)) was 55 +/- 8 impulse s(-1) during inflammation vs 97 +/- 7 impulse s(-1) in controls (P < 0.05). Normal firing rate was preserved following L-NIL pretreatment (112 +/- 16 impulse s(-1)) or acute administration of L-NIL (108 +/- 14 impulse s(-1)). A similar L-NIL dependent reduction was observed for 5-HT (250 micromol L(-1)) and mechanical ramp distension from 20 to 60 cmH(2)O (both P < 0.05). Intraluminal pressure peaks were decreased to 0.66 +/- 0.1 cmH(2)O during inflammation compared to 2.51 +/- 0.3 in controls (P < 0.01). Afferent sensitivity is decreased by an iNOS-dependent mechanism during intestinal inflammation which appears to be independent of the inflammatory response. This suggests that iNOS-dependent nitric oxide production alters afferent sensitivity during inflammation by interfering with signal transduction to afferent nerves rather than by attenuating intestinal inflammation.

Vagal modulation of intestinal afferent sensitivity to systemic LPS in the rat

The central nervous system modulates inflammation in the gastrointestinal tract via efferent vagal pathways. We hypothesized that these vagal efferents receive synaptic input from vagal afferents, representing an autonomic feedback mechanism. The consequence of this vagovagal reflex for afferent signal generation in response to LPS was examined in the present study. Different modifications of the vagal innervation or sham procedures were performed in anesthetized rats. Extracellular mesenteric afferent nerve discharge and systemic blood pressure were recorded in vivo before and after systemic administration of LPS (6 mg/kg iv). Mesenteric afferent nerve discharge increased dramatically following LPS, which was unchanged when vagal efferent traffic was eliminated by acute vagotomy. In chronically vagotomized animals, to eliminate both vagal afferent and efferent traffic, the increase in afferent firing 3.5 min after LPS was reduced to 3.2 +/- 2.5 impulses/s above baseline compared with 42.2 +/- 2.0 impulses/s in controls (P < 0.001). A similar effect was observed following perivagal capsaicin, which was used to eliminate vagal afferent traffic only. LPS also caused a transient hypotension (<10 min), a partial recovery, and then persistent hypertension that was exacerbated by all three procedures. Mechanosensitivity was increased 15 min following LPS but had recovered at 30 min in all subgroups except for the chronic vagotomy group. In conclusion, discharge in capsaicin-sensitive mesenteric vagal afferents is augmented following systemic LPS. This activity, through a vagovagal pathway, helps to attenuate the effects of septic shock. The persistent hypersensitivity to mechanical stimulation after chronic vagal denervation suggests that the vagus exerts a regulatory influence on spinal afferent sensitization following LPS.

Extracellular signal-regulated kinase-regulated microglia-neuron signaling by prostaglandin E2 contributes to pain after spinal cord injury

Many patients with traumatic spinal cord injury (SCI) report pain that persists indefinitely and is resistant to available therapeutic approaches. We recently showed that microglia become activated after experimental SCI and dynamically maintain hyperresponsiveness of spinal cord nociceptive neurons and pain-related behaviors. Mechanisms of signaling between microglia and neurons that help to maintain abnormal pain processing are unknown. In this study, adult male Sprague Dawley rats underwent T9 spinal cord contusion injury. Four weeks after injury when lumbar dorsal horn multireceptive neurons became hyperresponsive and when behavioral nociceptive thresholds to mechanical and thermal stimuli were decreased, we tested the hypothesis that prostaglandin E2 (PGE2) contributes to signaling between microglia and neurons. Immunohistochemical data showed specific localization of phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2), an upstream regulator of PGE2 release, to microglial cells and a neuronal localization of the PGE2 receptor E-prostanoid 2 (EP2). Enzyme immunoassay analysis showed that PGE2 release was dependent on microglial activation and ERK1/2 phosphorylation. Pharmacological antagonism of PGE2 release was achieved with the mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] and the microglial inhibitor minocycline. Cyclooxygenase-2 expression in microglia was similarly reduced by MEK1/2 inhibition. PD98059 and EP2 receptor blockade with AH6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) resulted in a decrease in hyperresponsiveness of dorsal horn neurons and partial restoration of behavioral nociceptive thresholds. Selective targeting of dorsal horn microglia with the Mac-1-SAP immunotoxin, a chemical conjugate of mouse monoclonal antibody to CD11b and the ribosome-inactivating protein saporin, resulted in reduced microglia staining, reduction in PGE2 levels, and reversed pain-related behaviors [corrected]. On the basis of these observations, we propose a PGE2-dependent, ERK1/2-regulated microglia-neuron signaling pathway that mediates the microglial component of pain maintenance after injury to the spinal cord.

Neuropathophysiology of functional gastrointestinal disorders

The investigative evidence and emerging concepts in neurogastroenterology implicate dysfunctions at the levels of the enteric and central nervous systems as underlying causes of the prominent symptoms of many of the functional gastrointestinal disorders. Neurogastroenterological research aims for improved understanding of the physiology and pathophysiology of the digestive subsystems from which the arrays of functional symptoms emerge. The key subsystems for defecation-related symptoms and visceral hyper-sensitivity are the intestinal secretory glands, the musculature and the nervous system that controls and integrates their activity. Abdominal pain and discomfort arising from these systems adds the dimension of sensory neurophysiology. This review details current concepts for the underlying pathophysiology in terms of the physiology of intestinal secretion, motility, nervous control, sensing function, immuno-neural communication and the brain-gut axis.

Serotonergic and non-serotonergic targets in the pharmacotherapy of visceral hypersensitivity

Visceral hypersensitivity is considered a key mechanism in the pathogenesis of functional gastrointestinal (GI) disorders. Targeting visceral hypersensitivity seems an attractive approach to the development of drugs for functional GI disorders. This review summarizes current knowledge on targets for the treatment of visceral hypersensitivity, and the status of current and future drug and probiotic treatment development, and the role of pharmacogenomic factors.

Mast cell-dependent excitation of visceral-nociceptive sensory neurons in irritable bowel syndrome

BACKGROUND & AIMS

Intestinal mast cell infiltration may participate to abdominal pain in irritable bowel syndrome (IBS) patients. However, the underlying mechanisms remain unknown. We assessed the effect of mast cell mediators released from the colonic mucosa of IBS patients on the activation of rat sensory neurons in vitro.

METHODS

Colonic mast cell infiltration and mediator release were assessed with quantitative immunofluorescence and immunoenzymatic assays. The effect of mucosal mediators was tested on mesenteric sensory nerve firing and Ca(2+) mobilization in dorsal root ganglia in rats.

RESULTS

Mediators from IBS patients, but not controls, markedly enhanced the firing of mesenteric nerves (14.7 +/- 3.2 imp/sec vs 2.8 +/- 1.5 imp/sec; P < .05) and stimulated mobilization of Ca(2+) in dorsal root ganglia neurons (29% +/- 4% vs 11% +/- 4%; P < .05). On average, 64% of dorsal root ganglia responsive to mediators were capsaicin-sensitive, known to mediate nociception. Histamine and tryptase were mainly localized to mucosal mast cells. IBS-dependent nerve firing and Ca(2+) mobilization were correlated with the area of the colonic lamina propria occupied by mast cells (r = 0.74; P < .01, and r = 0.78; P < .01, respectively). IBS-dependent excitation of dorsal root ganglia was inhibited by histamine H(1) receptor blockade and serine protease inactivation (inhibition of 51.7%; P < .05 and 74.5%; P < .05; respectively).

CONCLUSIONS

Mucosal mast cell mediators from IBS patients excite rat nociceptive visceral sensory nerves. These results provide new insights into the mechanism underlying visceral hypersensitivity in IBS.

Gastrointestinal pain in functional bowel disorders: sensory neurons as novel drug targets

Functional bowel disorders (FBDs) are defined by symptoms of gastrointestinal (GI) dysfunction, discomfort and pain in the absence of a demonstrable organic cause. Since the prevalence of FBDs, particularly functional dyspepsia and irritable bowel syndrome, can be as high as 20%, FBDs represent a significant burden in terms of direct healthcare and productivity costs. There is emerging evidence that the discomfort and pain experienced by many FBD patients is due to persistent hypersensitivity of primary afferent neurons, which may develop in response to infection, inflammation or other insults. This concept identifies vagal and spinal sensory neurons as important targets for novel therapies of GI hyperalgesia. Sensory neuron-specific targets can be grouped into three categories: receptors and sensors at the peripheral nerve terminals, ion channels relevant to nerve excitability and conduction and transmitter receptors. Particular therapeutic potential is attributed to targets that are selectively expressed by afferent neurons, such as the transient receptor potential channel TRPV1, acid-sensing ion channels and tetrodotoxin-resistant Na + channels.

Lipopolysaccharide-induced changes in mesenteric afferent sensitivity of rat jejunum in vitro: role of prostaglandins

Bacterial translocation across the intestinal mucosal barrier leads to a macrophage-mediated inflammatory response, visceral hyperalgesia, and ileus. Our aim was to examine how mediators released into mesenteric lymph following LPS treatment influence intestinal afferent sensitivity and the role played by prostanoids in any sensitization. Intestinal lymph was collected from awake rats following treatment with either saline or LPS (5 mg/kg ip). Extracellular multiunit afferent recordings were made from paravascular mesenteric nerve bundles supplying the rat jejunum in vitro following arterial administration of control lymph, LPS lymph, and LPS. Mesenteric afferent discharge increased significantly after LPS lymph compared with control lymph. Peak discharge occurred within 2 min and remained elevated for 5 to 8 min. This response was attenuated by pretreatment with naproxen (10 microM), and restored upon addition of prostaglandin E(2) (5 microM) in the presence of naproxen, but AH6809 (5 microM), an EP(1)/EP(2) receptor(s) antagonist, failed to decrease the magnitude of LPS lymph-induced response. LPS itself also stimulated mesenteric afferent discharge but was unaffected by naproxen. TNF-alpha was significantly increased in LPS lymph compared with control lymph (1,583 +/- 197 vs. 169 +/- 38 pg/ml, P < 0.01) but exogenous TNF-alpha failed to evoke any afferent nerve discharge. We concluded that inflammatory mediators released from the gut into mesenteric lymph during endotoxemia have a profound effect on afferent discharge. These mediators influence afferent firing via the release of local prostaglandins.

LPS-activated complement, not LPS per se, triggers the early release of PGE2by Kupffer cells

The intravenous injection of LPS rapidly evokes fever. We have hypothesized that its onset is mediated by prostaglandin (PG)E2quickly released by Kupffer cells (Kc). LPS, however, does not stimulate PGE2production by Kc as rapidly as it induces fever; but complement (C) activated by LPS could be the exciting agent. To test this hypothesis, we injected LPS (2 or 8 μg/kg) or cobra venom factor (CVF, an immediate activator of the C cascade that depletes its substrate, ultimately causing hypocomplementemia; 25 U/animal) into the portal vein of anesthetized guinea pigs and measured the appearance of PGE2, TNF-α, IL-1β, and IL-6 in the inferior vena cava (IVC) over the following 60 min. LPS (at both doses) and CVF induced similar rises in PGE2within the first 5 min after treatment; the rises in PGE2due to CVF returned to control in 15 min, whereas PGE2rises due to LPS increased further, then stabilized. LPS given 3 h after CVF to the same animals also elevated PGE2, but after a 30- to 45-min delay. CVF per se did not alter basal PGE2and cytokine levels and their responses to LPS. These in vivo effects were substantiated by the in vitro responses of primary Kc from guinea pigs to C (0.116 U/ml) and LPS (200 ng/ml). These results indicate that LPS-activated C rather than LPS itself triggers the early release of PGE2by Kc.

Sensitization of mesenteric afferents to chemical and mechanical stimuli following systemic bacterial lipopolysaccharide

BACKGROUNDS AND AIMS

The mechanisms underlying endotoxin-induced hyperalgesia remain unknown. We aimed to study the mechanisms underlying the sensitizing action of lipopolysaccharide (LPS) on intestinal afferent responses to mechanical and chemical stimuli.

METHODS

Extracellular recordings of jejunal afferent nerve discharge were obtained from pentobarbitone-anaesthetized rats.

RESULTS

Lipopolysaccharide (6 mg kg(-1), i.v.) stimulated a short-term, transient (<30 min) increase in chemosensitivity to systemic 5-HT (6 microg kg(-1)) and responses to mechanical distension and a delayed but maintained (>30 min) increase in spontaneous afferent discharge. Naproxen (10 mg kg(-1)) and the prostaglandin receptor antagonist AH6809 (1 mg kg(-1)) significantly attenuated both the short-term sensitization to mechanical distension and 5-HT and the long-term increase in baseline afferent firing following LPS. In contrast, the iNOS inhibitor aminoguanidine (15 mg kg(-1)) and the L-type calcium channel antagonist nifedipine (1 mg kg(-1)) both prolonged the period of afferent sensitization to distension and 5-HT without influencing the augmented baseline-firing rate. omega-Conotoxin GVIA attenuated the increase in afferent discharge to LPS, without any change in mechano- and chemosensitivity.

CONCLUSIONS

The long-term (>30 min) increase in afferent firing following systemic LPS involves neurogenic release of prostanoids. The short-term (<30 min) sensitization also appears to depend on prostanoid release, while nitric oxide production may serve to down-regulate LPS-induced afferent hypersensitivity.

Vagal selective effects of ruthenium red on the jejunal afferent fibre response to ischaemia in the rat

A variety of inflammatory mediators and local metabolites, have been implicated in the sensitivity of intestinal afferent fibres to brief periods of ischaemia and reperfusion. As yet, the contribution of the vanilloid transient receptor potential (TRPV)1 receptor to the response to intestinal ischaemia remains undetermined. In the present study, the effect of pretreatment with the competitive TRPV1 antagonist capsazepine and the non-selective TRPV channel antagonist ruthenium red, on the mesenteric afferent fibre response to ischaemia was examined. In control animals there was a reproducible biphasic increase in whole nerve afferent fibre activity during two brief periods of ischaemia. Treatment with ruthenium red significantly attenuated the early phase increase in afferent fibre activity during ischaemia. However, capsazepine treatment did not significantly alter the afferent fibre response to either ischaemia or reperfusion. Further experiments in chronically vagotomized animals indicated that the early phase response to ischaemia was mediated via vagal afferent fibres. The mechanism via which ruthenium red selectively inhibited vagal afferent fibres during ischaemia is unknown, but it does not appear to involve blockade of the TRPV1 receptor.

Enteric neuroimmunophysiology and pathophysiology

Minute-to-minute behavior of the bowel, whether it is normal or disordered, is determined by integrative functions of the enteric nervous system (ENS). Information input processed by the ENS is derived from local sensory receptors, the central nervous system, and immune/inflammatory cells including mast cells. Enteric mast cells use the power of the immune system for detection of antigenic threats and for long-term memory of the identity of the specific antigens. Specific antibodies attach to the mast cells and enable the mast cell to detect sensitizing antigens when they reappear in the gut lumen. Should the sensitizing antigen reappear, mast cells detect it and signal its presence to the ENS. The ENS interprets the mast cell signal as a threat and calls up from its program library secretory and propulsive motor behavior that is organized to eliminate the threat rapidly and effectively. Operation of the alarm program protects the individual, but at the expense of symptoms that include cramping abdominal pain, fecal urgency, and diarrhea. Enteric mast cells use immunologic memory functions to detect foreign antigens as they appear and reappear throughout the life of the individual. Mast cells use paracrine signaling for the transfer of chemical information to the neural networks of the ENS. Integrative circuits in the ENS receive and interpret the chemical signals from the mast cells. Signals from the mast cells are interpreted by the ENS as a labeled code for the presence of a threat in the intestinal lumen.

Role of vasoactive intestinal peptide and inflammatory mediators in enteric neuronal plasticity

Complex circuits involving both local intrinsic neurones (i.e. enteric nervous system; ENS) and extrinsic neurones achieve nervous control of digestive functions. The ENS is comprised of many functionally different types of neurons: sensory neurons, interneurons and secreto-motor neurons. Each neuronal population is required to manifest local reflex behavior and is central to the regulation of both motor and secretory activities. It must be emphasized, however, that not only muscle and secretory cells but also other intestinal cells are targeted by enteric neurones, i.e. endocrine cells, interstitial cells of Cajal, immune cells, blood vessels and enteric glia. In addition to the ENS the gastrointestinal tract receives an extrinsic innervation by sympathetic, parasympathetic and sensory fibres. Neuronal projections from the intestine to prevertebral ganglia also exist. Taken together, the picture of a complex nervous regulation of digestive functions highly integrated with the central nervous system and the rest of the autonomic nervous system has emerged. The ENS is adaptive and plastic, but also vulnerable, system and ENS disturbances may be of pathogenic importance in functional bowel disease. In particular the interplay between the enteric neurones and the immune cells is suggested to be of crucial importance. The review discusses possible roles of the mediators vasoactive intestinal peptide (VIP) and prostanoids in ENS plasticity in response to injury and inflammation.

Stimulation of proteinase-activated receptor 2 excites jejunal afferent nerves in anaesthetised rats

Proteinase-activated receptor 2 (PAR2) is a receptor for mast cell tryptase and trypsins and might participate in brain-gut communication. However, evidence that PAR2 activation can lead to afferent impulse generation is lacking. To address this issue, we examined the sensitivity of jejunal afferent nerves to a hexapeptide agonist of PAR2, SLIGRL-NH2, and the modulation of the resulting response to treatment with drugs and vagotomy. Multiunit recordings of jejunal afferent activity were made using extracellular recording techniques in anaesthetised male rats. SLIGRL-NH2 (0.001-1 mg kg-1, I.V.) increased jejunal afferent firing and intrajejunal pressure. The reverse peptide sequence (1 mg kg-1, I.V.), which does not stimulate PAR2, was inactive. Naproxen (10 mg kg-1, I.V.), but not a cocktail of omega-conotoxins GVIA and SVIB (each at 25 mug kg-1, I.V.), curtailed both the afferent response and the intrajejunal pressure rise elicited by the PAR2 agonist. Although neither treatment modulated the peak magnitude of the afferent firing, they each altered the intestinal motor response, unmasking an initial inhibitory component. Nifedipine (1 mg kg-1, I.V.) reduced the peak magnitude of the afferent nerve discharge and abolished the initial rise in intrajejunal pressure produced by SLIGRL-NH2. Vagotomy did not significantly influence the magnitude of the afferent response to the PAR2 agonist, which involves a contribution from capsaicin-sensitive fibres. In conclusion, intravenous administration of SLIGRL-NH2 evokes complex activation of predominantly spinally projecting extrinsic intestinal afferent nerves, an effect that involves both direct and indirect mechanisms.

Facilitation by endogenous prostaglandins of capsaicin-induced gastric protection in rodents through EP2 and IP receptors

We investigated the role that prostaglandins (PGs) and EP receptors play in facilitating the gastroprotective action of capsaicin against HCl/ethanol in rats and mice. Male Sprague-Dawley rats and C57BL/6 mice were used after 18 h of fasting. The animals were given HCl/ethanol (60% in 150 mM HCl) p.o. and killed 1 h later. Capsaicin or various EP agonists were given p.o. 30 min or i.v. 10 min before HCl/ethanol. In some cases, indomethacin or various EP agonists were given s.c. 30 min or i.v 10 min before capsaicin, respectively. Gastric lesions induced by HCl/ethanol were significantly inhibited by PGE(2) as well as capsaicin. The effect of PGE(2) was antagonized by ONO-AE-829 (EP1 antagonist), whereas the capsaicin action was mitigated by indomethacin as well as sensory deafferentation but not by ONO-AE-829. The generation of mucosal PGE(2) was not affected by either capsaicin or sensory deafferentation, but was significantly inhibited by indomethacin. Although neither butaprost (EP2), ONO-NT-012 (EP3), nor 11-deoxy PGE1 (EP4) alone had any effect on HCl/ethanol-induced gastric lesions, only butaprost restored the protective action of capsaicin in the presence of indomethacin. Capsaicin provided a protective action against HCl/ethanol-induced gastric lesions in wild-type (+/+) mice in an indomethacin-sensitive manner, and this action was similarly observed in EP1 (-/-) and EP3 (-/-) mice but not in the animals lacking IP receptors. These results suggest that capsaicin exhibits gastric cytoprotection, essentially by stimulating sensory neurons, and this action is facilitated by endogenous PGs through EP2/IP receptors, probably sensitizing the sensory neurons to capsaicin.

Sensory neurone responses to mucosal noxae in the upper gut: relevance to mucosal integrity and gastrointestinal pain

The digestive tract is supplied by extrinsic and intrinsic sensory neurones that, together with endocrine and immune cells, form a surveillance network that is essential to gut function. This article focuses on the responses of extrinsic afferent neurones to chemical insults of the gastrointestinal mucosa and their pathophysiological relevance to mucosal integrity and abdominal pain. Within the gastroduodenal region, spinal afferents subserve an emergency function because, in case of alarm by influxing acid, they stimulate mechanisms of mucosal protection via an efferent-like release of transmitters. Other sensory neurones signal chemical noxae to the brain, a task that is not confined to spinal afferents because vagal afferents communicate gastric acid and peripheral immune challenges to the brainstem and in this way elicit autonomic, endocrine, affective and behavioural reactions. Emerging evidence indicates that hypersensitivity of extrinsic afferent pathways to mechanical and chemical stimuli makes an important contribution to the abdominal hyperalgesia seen in functional dyspepsia and irritable bowel syndrome. Sensitization may be brought about by inflammatory processes that lead to up-regulation and functional alterations of receptors and ion channels on sensory neurones. Such sensory neurone-specific molecules, which include vanilloid (capsaicin) receptors, may represent important targets for novel drugs to treat abdominal pain.

Gastric ulcerogenic responses following barrier disruption in knockout mice lacking prostaglandin EP1 receptors

BACKGROUND/AIMS

Endogenous prostaglandins (PGs) are considered to play a pivotal role in maintaining the mucosal integrity of the stomach after injury. In the present study, we evaluated the mucosal ulcerogenic and mucosal blood flow (GMBF) responses in the stomach after damage by taurocholate (TC) in knockout mice lacking EP1 or EP3 receptors.

METHODS

Under urethane anaesthesia, a mouse stomach was mounted in an ex vivo chamber, exposed to 20 mmol/L TC for 20 min and treated with 20 mmol/L HCl before and after TC. GMBF was measured with a laser Doppler flowmeter.

RESULTS

Mucosal exposure to TC in wild-type mice caused a marked decrease in potential difference (PD), followed by an increase in H+ loss and GMBF. The decreased PD was gradually normalized after removal of TC from the chamber, with minimal damage in the mucosa 1 h after TC treatment. This hyperaemic response was inhibited by indomethacin, resulting in severe lesions in the mucosa without any change in PD or H+ loss. None of these responses induced by TC were altered in EP3-/- mice. However, in mice lacking EP1 receptors, TC treatment did not increase GMBF, despite causing PD reduction and acid loss, and resulted in severe damage in the mucosa. These responses were closely similar to those observed in animals pretreated with ONO-8711, a EP1 receptor antagonist. Mucosal PGE2 content was significantly increased after TC, similarly in all groups of mice.

CONCLUSION

These results confirm a mediator role for PGE2 in gastric hyperaemic response following mucosal exposure to TC and suggest that endogenous PGs may contribute to maintaining mucosal integrity after barrier disruption, mainly through activation of the EP1 receptor subtype.

Small bowel motility

The publications relevant to small bowel motility have been concentrated during the past year in several main areas: further characterization of normal patterns of small bowel motor activity and transit, physiologic control mechanisms, visceral hypersensitivity, inflammation and motility, disease processes and dysmotility, and novel pharmacologic approaches to altered sensorimotor activity.

Gastrointestinal afferents as targets of novel drugs for the treatment of functional bowel disorders and visceral pain

An intricate surveillance network consisting of enteroendocrine cells, immune cells and sensory nerve fibres monitors the luminal and interstitial environment in the alimentary canal. Functional bowel disorders are characterized by persistent alterations in digestive regulation and gastrointestinal discomfort and pain. Visceral hyperalgesia may arise from an exaggerated sensitivity of peripheral afferent nerve fibres and/or a distorted processing and representation of gut signals in the brain. Novel strategies to treat these sensory bowel disorders are therefore targeted at primary afferent nerve fibres. These neurons express a number of molecular traits including transmitters, receptors and ion channels that are specific to them and whose number and/or behaviour may be altered in chronic visceral pain. The targets under consideration comprise vanilloid receptor ion channels, acid-sensing ion channels, sensory neuron-specific Na(+) channels, P2X(3) purinoceptors, 5-hydroxytryptamine (5-HT), 5-HT(3) and 5-HT(4) receptors, cholecystokinin CCK(1) receptors, bradykinin and prostaglandin receptors, glutamate receptors, tachykinin and calcitonin gene-related peptide receptors as well as peripheral opioid and cannabinoid receptors. The utility of sensory neuron-targeting drugs in functional bowel disorders will critically depend on the compounds' selectivity of action for afferent versus enteric or central neurons.

Receptors and transmission in the brain-gut axis: potential for novel therapies. I. Receptors on visceral afferents

Visceral afferents are the information superhighway from the gut to the central nervous system. These sensory nerves express a wide range of membrane receptors that can modulate their sensitivity. In this themes article, we concentrate on those receptors that enhance the excitability of visceral afferent neurons. Some receptors are part of a modality-specific transduction pathway involved in sensory signaling. Others, which are activated by substances derived from multiple cellular sources during ischemia, injury, or inflammation, act in a synergistic fashion to cause acute or chronic sensitization of the afferent nerves to mechanical and chemical stimuli. Such hypersensitivity is the hallmark of conditions such as irritable bowel syndrome. Accordingly, these receptors represent a rational target for drug treatments aimed at attenuating both the inappropriate visceral sensation and the aberrant reflex activity that are the foundation for alterations in bowel function.