A new model of chronic visceral hypersensitivity in adult rats induced by colon irritation during postnatal development

Pooled analysis of brain activity in irritable bowel syndrome and controls during rectal balloon distension

BACKGROUND

Brain-imaging literature of irritable bowel syndrome (IBS) suggests an abnormal brain-gut communication. We analyzed the literature to evaluate and compare the aspects of brain activity in individuals with IBS and control subjects experiencing controlled rectal stimulation.

METHODS

PubMed was searched until September 2010. Data from 16 articles reporting brain activity during rectal balloon distensions in IBS compared to control groups was analyzed. Prevalence rates and pairwise activations were assessed using binomial distributions for 11 selected regions of interest. The data were aggregated to adjust for center effect.

KEY RESULTS

There was considerable variability in the literature regarding regions and their activity patterns in controls and individuals with IBS. There was no significant difference found in the thalamus, anterior cingulate cortex, posterior cingulate cortex, and prefrontal cortex, however, results show limited evidence of consensus for the anterior insula (AI) (P = 0.22). Pairwise activity results suggest that pairs involving the AI tend to have more consistent activity together than pairs which do not involve the AI (posterior insula and AI, P = 0.08; posterior cingulate cortex and AI, P = 0.16), however, no pairwise evaluation reached significance.

CONCLUSIONS & INFERENCES

Our pooled analysis demonstrates that the literature reports are quite heterogeneous but there is some evidence that there may be patterns of higher activity more common in individuals with IBS than in controls. A consensus, though, regarding study designs, analysis approach and reporting could create a clearer understanding of brain involvement in IBS pathophysiology.

Maternal separation as a model of brain-gut axis dysfunction

RATIONALE

Early life stress has been implicated in many psychiatric disorders ranging from depression to anxiety. Maternal separation in rodents is a well-studied model of early life stress. However, stress during this critical period also induces alterations in many systems throughout the body. Thus, a variety of other disorders that are associated with adverse early life events are often comorbid with psychiatric illnesses, suggesting a common underlying aetiology. Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is thought to involve a dysfunctional interaction between the brain and the gut. Essential aspects of the brain-gut axis include spinal pathways, the hypothalamic pituitary adrenal axis, the immune system, as well as the enteric microbiota. Accumulating evidence suggest that stress, especially in early life, is a predisposing factor to IBS.

OBJECTIVE

The objective of this review was to assess and compile the most relevant data on early life stress and alterations at all levels of the brain gut axis.

RESULTS

In this review, we describe the components of the brain-gut axis individually and how they are altered by maternal separation. The separated phenotype is characterised by alterations of the intestinal barrier function, altered balance in enteric microflora, exaggerated stress response and visceral hypersensitivity, which are all evident in IBS.

CONCLUSION

Thus, maternally separated animals are an excellent model of brain-gut axis dysfunction for the study of disorders such as IBS and for the development of novel therapeutic interventions.

Suspended moxibustion relieves chronic visceral hyperalgesia and decreases hypothalamic corticotropin-releasing hormone levels

AIM: To evaluate the effect of suspended moxibustion (SM) on rectal sensory thresholds and to analyze the possible mechanisms involved in SM treatment of chronic visceral hypersensitivity (CVH) in rats.

METHODS: SM was administered once daily to 37-d-old CVH rats for 7 d. The two pairs of acupoints (ST25 and ST37, bilateral) were simultaneously treated with SM. Each treatment lasted for 30 min. Rats undergoing treatment with SM were not anesthetized. Untreated CVH rats and normal rats were used as controls. The abdominal withdrawal reflex was determined 30-90 min after the seven treatments. The hypothalamic corticotropin-releasing hormone (CRH) mRNA level was measured using real-time quantitative reverse transcription-polymerase chain reaction.

RESULTS: We found that SM treatment significantly decreased visceral sensitivity to colorectal distention in this rat model. In treated animals, SM also decreased the relative hypothalamic CRH mRNA expression level to control levels.

CONCLUSION: Lower hypothalamic CRH levels may mediate the beneficial effects of SM in this rat irritable bowel syndrome model.

Increased wind-up to heat pain in women with a childhood history of functional abdominal pain

Idiopathic or functional abdominal pain (FAP) is common in school-age children and typically reflects a functional gastrointestinal disorder (FGID). FGIDs in adults have been distinguished by enhanced responses of the central nervous system to pain stimuli, known as central sensitization. This study investigated whether adolescents and young adults with a history of pediatric FAP (n=144), compared with well control subjects (n=78), showed enhanced central sensitization demonstrated by greater temporal summation (wind-up) to brief, repetitive heat pulses. We also assessed the role of gender and trait anxiety in wind-up to heat pain. Women with a history of FAP showed greater wind-up to heat pain than men with a history of FAP (P<.05) and well control subjects of both genders (P<.05). Results were similar for FAP participants whose abdominal pain was ongoing at follow-up and those whose pain had resolved. Although anxiety was significantly higher in the FAP group compared with control subjects (P<.01) and in women compared with men (P<.05), anxiety did not explain the increased wind-up observed in women with a childhood history of FAP. Results suggest that women with a pediatric history of FAP may have a long-term vulnerability to pain associated with enhanced central nervous system responses to pain stimuli. Young women with a childhood history of functional abdominal pain may have a long-term vulnerability to pain that is associated with enhanced responses of the central nervous system to pain stimuli.

Cow's-milk allergy is a risk factor for the development of FGIDs in children

OBJECTIVES

Functional gastrointestinal disorders (FGIDs) are common in children. Their pathogenesis remains unknown and is most likely multifactorial. We hypothesized that noninfectious causes of inflammation affecting the gastrointestinal (GI) tract early in life, such as cow's-milk allergy (CMA), can predispose to the development of FGIDs later in childhood.

PATIENTS AND METHODS

Case-control study. Subjects were patients between 4 and 18 years diagnosed with CMA in the first year of life at Children's Memorial Hospital in Chicago, IL, between January 2000 and June 2009. Diagnosis of CMA was based on history and clinical findings. Siblings 4 to 18 years of age without a history of CMA were selected as controls. Cases completed the parental form of the Pediatric Gastrointestinal Symptoms Rome III version questionnaire to assess for GI symptoms.

RESULTS

Fifty-two subjects (mean age 8.1 ± 4.48 years, 62% girls) and 53 controls (mean age 9.7 ± 4.20 years, 55% girls) participated in the study. Twenty-three of 52 subjects (44.2%) reported GI symptoms that included abdominal pain, constipation, or diarrhea compared with 11 of 53 controls (20.75%) (odds ratio 3.03, P = 0.01). Abdominal pain was significantly more common in cases (16/52, 30.8%) versus controls (5/53, 9.43%) (odds ratio 4.27 [1.43-12.7]) (χ² = 7.47, P = 0.01). Abnormal stool habits were more common in cases (15/52, 28.8%) versus controls (7/53, 13.2%), but the difference was not statistically significant. Ten of 52 subjects (19.2%) met the Questionnaire on Pediatric Gastrointestinal Symptoms Rome III version criteria for diagnosis of an FGID (7 irritable bowel syndrome, 2 functional dyspepsia, 1 functional abdominal pain), whereas none in the control group did.

CONCLUSIONS

CMA constitutes a risk factor for the development of FGIDs in children.

Systematic review of animal models of post-infectious/post-inflammatory irritable bowel syndrome

AIMS

Post-infectious irritable bowel syndrome (PI-IBS) is a subset of IBS which occurs after an episode of acute gastrointestinal infections. The mechanisms of PI-IBS are not fully understood. Currently, numerous animal models have been used in the study of PI-IBS. This article reviews the strengths and weaknesses of these models.

METHODS

All relevant articles were identified by searching in Ovid SP from 1962, the year the term PI-IBS was coined, up to December 31, 2009. The types of model were categorized as either post-infectious or post-inflammatory, and the characteristics of each kind of model were listed.

RESULTS

Based on our literature search, 268 articles were identified. Of those articles, 50 were included in this review. The existing PI-IBS models include infection with bacteria (e.g., Campylobacter jejuni, Salmonella enterica, and Campylobacter rodentium), and infection with parasites (e.g., Trichinella spiralis, Nippostrongylus brasiliensis, and Cryptosporidium parvum). The post-inflammatory IBS models are commonly induced with chemical agents, such as acetic acid, deoxycholic acid, dextran sulfate sodium, mustard oil, zymosan, and trinitrobenzene sulfonic acid (TNBS). TNBS is the most commonly used agent for post-inflammatory IBS models, but the experimental protocol varies. These models have one or more aspects similar to IBS patients.

CONCLUSIONS

Different methods have been used for the development of post-infectious or post-inflammatory IBS models. Each model has its weaknesses and strengths. More studies are needed to establish post-infection IBS models using more common pathogens. A standard protocol in developing TNBS-induced post-inflammatory IBS model is needed.

Is it all central sensitization? Role of peripheral tissue nociception in chronic musculoskeletal pain

Fibromyalgia syndrome (FM) is a highly prevalent musculoskeletal disorder that is often accompanied by somatic hyperalgesia (enhanced pain from noxious stimuli). Neural mechanisms of somatic hyperalgesia have been analyzed via quantitative sensory testing of FM patients. Results of these studies suggest that FM pain is associated with widespread primary and secondary cutaneous hyperalgesia, which are dynamically maintained by tonic impulse input from deep tissues and likely by brain-to-spinal cord facilitation. Enhanced somatic pains are accompanied by mechanical hyperalgesia and allodynia in FM patients as compared with healthy controls. FM pain is likely to be at least partially maintained by peripheral impulse input from deep tissues. This conclusion is supported by results of several studies showing that injection of local anesthetics into painful muscles normalizes somatic hyperalgesia in FM patients.

Proteomic analysis of colonic mucosa in a rat model of irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most common functional disorders of the gastrointestinal tract. It is characterized by abdominal pain and changes in bowel habits. Various studies have investigated the pathophysiologic processes underlying IBS, but the mechanism remains poorly understood. In the present study, we established an IBS model and identified differentially expressed proteins in colon tissue of IBS rats compared with healthy controls by 2-D gel electrophoresis, MALDI-TOF-MS, and Western blot analysis. Our results showed that 13 of the 1396 protein spots on 2-D gel were differently expressed between the IBS and control groups. Ontological analysis of these proteins revealed primary roles in catalytic activity (protein disulfide-isomerase A3, glyoxalase I, cathepsin S, alpha-enolase), structural support (cytokeratin 8), antioxidant activity (peroxiredoxin-6), protein binding (transgelin, serpin peptidase inhibitor B5), and signal transduction (40S ribosomal protein SA). Protein disulfide-isomerase A3 and cytokeratin 8 overexpression in IBS were confirmed by Western blot. The findings indicate that multiple proteins are involved in IBS processes that influence intestinal tract immunity, inflammation, and nerve regulation. Our study provides useful candidate genes and proteins for further investigation.

Low-grade mucosal inflammation induces colonic PAR-2 activation and visceral hypersensitivity in mice

AIM: To detect the expression of protease-activated receptor-2 (PAR-2) in the colon and substance P (SP) and calcitonin gene-related peptide (CGRP) in the cornu dorsale medullae spinalis and to explore the relationship between the activation of PAR-2 and visceral hypersensitivity in mice with dextran sulfate sodium (DSS)-induced low-glade colonic mucosal inflammation (LGI).

METHODS: Thirty-six C57BL/6 mice were randomly divided into two groups: LGI group and control group. The LGI group was given 1.5% DSS solution for 5 d and distilled water for another 10 d, while the control group was given distilled water only. After treatment, the myoelectric activity of the abdominal wall at different levels of colorectal distension (CRD) was recorded. The expression of SP and CGRP in the cornu dorsale medullae spinalis and PAR-2 in the colonic mucosa was detected by immunohistochemistry.

RESULTS: After treatment, colonic histological index (HI) in the LGI group was 1.500 ± 0.926. When the colon was distended to a pressure of 15 mmHg, the myoelectric activity of the abdominal wall in the LGI group was comparable to that in the control group (27.958 μV ± 1.660 μV vs 26.947 μV ± 0.854 μV, P > 0.05). However, the myoelectric activity of the abdominal wall was significantly higher in the LGI group than in the control group when the colon was distended to a pressure of 30, 45 or 60 mmHg (33.455 μV ± 3.786 μV vs 31.253 μV ± 3.842 μV; 46.848 μV ± 4.038 μV vs 37.267 μV ± 2.542 μV; 47.207 μV ± 18.151 μV vs 33.798 μV ± 8.415 μV, all P < 0.05). The integrated optical density (IA) of PAR-2 staining in the distal colon was significantly higher in the LGI group than in the control group. The IA of SP and CGRP staining in the spine cord was also significantly higher in the LGI group than in the control group (40.769 ± 8.422 vs 21.718 ± 4.131; 30.288 ± 13.530 vs 10.788 ± 4.490; 46.829 ± 26.261 vs 13.997 ± 3.340, all P < 0.05). There is a positive correlation between the expression of PAR-2 and SP and between the expression of PAR-2 and CGRP in the LGI group (r = 0.622, P < 0.05, r = 0.588, P < 0.05). The expression of PAR-2, SP or CGRP was closely correlated with the myoelectric activity of the abdominal wall in the LGI group (r = 0.439-0.835, P < 0.05).

CONCLUSION: Low-grade mucosal inflammation induces visceral hypersensitivity in mice possibly by activating colonic PAR-2.

Chronological assessment of mast cell-mediated gut dysfunction and mucosal inflammation in a rat model of chronic psychosocial stress

Life stress and mucosal inflammation may influence symptom onset and severity in certain gastrointestinal disorders, particularly irritable bowel syndrome (IBS), in connection with dysregulated intestinal barrier. However, the mechanism responsible remains unknown. Crowding is a validated animal model reproducing naturalistic psychosocial stress, whose consequences on gut physiology remain unexplored. Our aims were to prove that crowding stress induces mucosal inflammation and intestinal dysfunction, to characterize dynamics in time, and to evaluate the implication of stress-induced mast cell activation on intestinal dysfunction. Wistar-Kyoto rats were submitted to 15 days of crowding stress (8 rats/cage) or sham-crowding (2 rats/cage). We measured spontaneous and corticotropin-releasing factor-mediated release of plasma corticosterone. Stress-induced intestinal chrono-pathobiology was determined by measuring intestinal inflammation, epithelial damage, mast cell activation and infiltration, and intestinal barrier function. Corticosterone release was higher in crowded rats throughout day 15. Stress-induced mild inflammation, manifested earlier in the ileum and the colon than in the jejunum. While mast cell counts remained mostly unchanged, piecemeal degranulation increased along time, as the mucosal content and luminal release of rat mast cell protease-II. Stress-induced mitochondrial injury and increased jejunal permeability, both events strongly correlated with mast cell activation at day 15. Taken together, we have provided evidences that long-term exposure to psychosocial stress promotes mucosal inflammation and mast cell-mediated barrier dysfunction in the rat bowel. The notable resemblance of these findings with those in some IBS patients, support the potential interest and translational validity of this experimental model for the research of stress-sensitive intestinal disorders, particularly IBS.

Neonatal colon insult alters growth factor expression and TRPA1 responses in adult mice

Inflammation or pain during neonatal development can result in long-term structural and functional alterations of nociceptive pathways, ultimately altering pain perception in adulthood. We have developed a mouse model of neonatal colon irritation (NCI) to investigate the plasticity of pain processing within the viscerosensory system. Mouse pups received an intracolonic administration of 2% mustard oil (MO) on postnatal days 8 and 10. Distal colons were processed at subsequent timepoints for myeloperoxidase (MPO) activity and growth factor expression. Adult mice were assessed for visceral hypersensitivity by measuring the visceromotor response during colorectal distension. Dorsal root ganglion (DRG) neurons from adult mice were retrogradely labeled from the distal colon and calcium imaging was used to measure transient receptor potential vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1) responses to acute application of capsaicin and MO, respectively. Despite the absence of inflammation (as indicated by MPO activity), neonatal exposure to intracolonic MO transiently maintained a higher expression level of growth factor messenger RNA (mRNA). Adult NCI mice displayed significant visceral hypersensitivity, as well as increased sensitivity to mechanical stimulation of the hindpaw, compared to control mice. The percentage of TRPA1-expressing colon afferents was significantly increased in NCI mice, however they displayed no increase in the percentage of TRPV1-immunopositive or capsaicin-sensitive colon DRG neurons. These results suggest that early neonatal colon injury results in a long-lasting visceral hypersensitivity, possibly driven by an early increase in growth factor expression and maintained by permanent changes in TRPA1 function.

Visceral hypersensitivity induced by activation of transient receptor potential vanilloid type 1 is mediated through the serotonin pathway in rat colon

This study aimed to clarify the relationship between TRPV1 activation-induced visceral pain and the serotonin pathway in the colon of rats. The effects of para-chlorophenylalanine (pCPA) on visceral pain threshold pressure were assessed in capsaicin -induced visceral pain of rats. The expression of TRPV1 in the colon was examined by immunohistochemistry and Western blot analysis, and TRPV1 excitability in dorsal root ganglion (DRG) neurons was examined by whole-cell patch-clamp recording in pCPA-treated rats. Calcineurin and Ca(2+)-calmodulin-dependent kinase II (CaMKII), the important proteins in maintaining TRPV1 function in the colon, were also tested by Western blot analysis and immunofluorescence staining. Results showed that pCPA significantly increased the capsaicin-induced visceral pain threshold by 2.3-fold, and the enhanced visceral pain threshold corresponded with decreased 5-HT content (58% depleted) and enterochromaffin cell number (80% reduced). The reduced excitability of TRPV1 in DRG neurons, instead of changed TRPV1 expression, is responsible for the enhanced visceral pain threshold in 5-HT-depleted rats, and the mechanism may be related to the decreased expression of pCaMKII. These results indicate that visceral hypersensitivity induced by TRPV1 activation is modulated through 5-HT pathways and the attenuated function of TRPV1 and decreased protein expression of pCaMKII may play an important role in capsaicin-induced TRPV1 desensitization under 5-HT-depleted condition. The important role of TRPV1 and 5-HT in generating and maintaining visceral hypersensitivity may provide insights for the treatment of visceral hypersensitivity.

Ameliorating effects of mirtazapine on visceral hypersensitivity in rats with neonatal colon sensitivity

BACKGROUND

The aim was to investigate the effects of mirtazapine on visceral hypersensitivity and gastric emptying in an established rodent model of colonic sensitization.

METHODS

Twenty colonic sensitized rats and 20 matched controls were used. Visceral sensitivity during colorectal distension (CRD) was assessed by the measurement of abdominal electromyogram (EMG) with the pressures of 20, 40, and 60 mmHg. Mirtazapine with doses of 1, 5, and 10 mg kg(-1) were administered orally. Gastric emptying and small intestinal transit were performed in a separated experiment after gavage of 1.5 mL of phenol red solution.

KEY RESULTS

(i) Visceral hypersensitivity after neonatal colonic sensitization was confirmed. (ii) Mirtazapine dose-dependently reduced visceral hypersensitivity in the colonic sensitized rats. The increases in EMG during CRD at 40, 60 mmHg were, 17.59 +/- 6.49 and 26.04 +/- 8.30, respectively, with saline session, and substantially reduced to 10.0 +/- 5.95 (P = 0.02 vs corresponding saline) and 12.58 +/- 7.43 (P < 0.001 vs saline) with mirtazapine at 10 mg kg(-1). Similar findings were noted at doses of 5 and 1 mg kg(-1) at a lesser degree. In the control rats, mirtazapine-reduced visceral sensitivity only during CRD at 60 mmHg. (iii) Mirtazapine 10 mg kg(-1) significantly accelerated gastric emptying (P = 0.045) but slightly and marginally delayed intestinal transit (P = 0.058) the colonic sensitized rats.

CONCLUSIONS & INFERENCES

Mirtazapine dose-dependently ameliorates visceral hypersensitivity in colonic sensitized rats. Mirtazapine at a high dose improves delayed gastric emptying in colonic sensitized rats but slightly and marginally delays small intestinal transit. Its roles in altering gastrointestinal motility need further investigation.

Effects of moxibustion on dynorphin and endomorphin in rats with chronic visceral hyperalgesia

AIM: To observe the analgesic effects of moxibustion in rats with chronic visceral hyperalgesia and its influence on the concentration of dynorphin (Dyn) and endomorphin (EM) in spinal cord.

METHODS: The rat model of chronic visceral hyperalgesia was established by colorectal distention (CRD). In moxibustion (MX) group, moxibustion was applied once daily for 7 d; in sham moxibustion (SM) group, moxibustion was given to the same acupoints but with the non-smoldered end of the moxa stick. Model control (MC) group and normal control group were also studied. The scoring system of abdominal withdrawal reflex was used to evaluate visceral pain for behavioral assessment. Enzyme linked immunosorbent assay was performed to determine the concentrations of Dyn and EM in spinal cord.

RESULTS: Moxibustion significantly decreased visceral pain to CRD in this rat model, and no significant difference was detected between the SM group and the MC group. In MX group, moxibustion also increased the concentrations of Dyn and EM in spinal cord, and no significant difference was found between the SM group and the MC group.

CONCLUSION: Moxibustion therapy can significantly enhance the pain threshold of rats with chronic visceral hyperalgesia, and the effect may be closely related to the increased concentration of Dyn and EM in spinal cord.

Effect of electroacupuncture on visceral hyperalgesia, serotonin and fos expression in an animal model of irritable bowel syndrome

Background/Aims

While it is well established that acupuncture relieves somatic pain, its therapeutic effect on visceral pain such as irritable bowel syndrome (IBS) is unclear. We evaluated the effect of acupuncture in treating visceral hyperalgesia in an animal model.

Methods

Sprague-Dawley rats (n = 8 per group) with prior neonatal maternal separation stress were randomly allocated to receive 3-day treatment of either electroacupuncture (EA) or sham acupuncture at acupoint ST-36. Another group of rats without prior maternal separation was included as non-handled controls. Colorectal distension was performed on the day after acupuncture treatment. The 3 groups were compared for pain threshold as determined by abdominal withdrawal reflex and visceromotor response as measured by electromyogram. Colon, spinal cord, and brainstem were sampled for topographic distribution and quantitative assessment of serotonin and Fos expression by immunohistochemistry.

Results

Rats in EA group had significantly higher pain threshold compared to those in sham acpuncture group (25.0 ± 5.7 mmHg vs 18.7 ± 5.2 mmHg, p = 0.01) and it was comparable with that of non-handled treatment naïve controls (29.4 ± 9.3 mmHg, p = 0.28). They also had lower visceromotor response as measured by electromyogram compared to those received sham acupuncture at all colorectal distension pressures. EA significantly suppressed Fos expression in doral raphe nuclei of brainstem, superficial dorsal horn of spinal cord and colonic epithelium but suppressed 5-HT expression only in brainstem and spinal cord.

Conclusions

Electro acupuncture attenuates visceral hyperlagesia through down-regulation of central serotonergic activities in the brain-gut axis.

Effects of neonatal inflammation on descending modulation from the rostroventromedial medulla

Cutaneous tissue inflammation during the first postnatal week is known to alter long-term development of spinal cord nociceptive circuitry and to alter behavioral responses to noxious stimuli in adult animals. The impact of neonatal inflammation on descending projections arising from supraspinal sites that modulate spinal nociceptive processing is unknown. In the present study, we investigated if altered behavioral responses to pain in adult animals after neonatal inflammation are associated with changes in descending modulation of nocifensive responses elicited from the rostroventromedial medulla (RVM) in lightly anesthetized rats. Compared to handled control animals, hindpaw injection of 0.25% carrageenan (CG) at postnatal day 3 produced adult basal hypoalgesia and increased hyperalgesia 24 h after reinflammation with Complete Freund's Adjuvant (CFA) in awake animals. These effects were specific to the neonatally treated hindpaw, partially replicating previous findings, but were absent in lightly anesthetized animals. However, focal electrical stimulation of the RVM in lightly anesthetized CG treated animals produced significantly greater descending inhibition of nocifensive responses to noxious thermal stimuli applied to the hindpaws and the tail. These effects were partially replicated by intra-RVM microinjection of AMPA. No differences in the efficacy of RVM stimulation between CG and control animals were observed 24h after reinflammation with CFA. These findings indicate that neonatal tissue injury and inflammation produces lasting alterations in descending modulatory systems that modify nociceptive processing. Taken together with previous studies, these results indicate that changes in pain sensitivity following neonatal tissue injury involve long-term alterations in spinal and supraspinal circuitry.

Functional abdominal pain in childhood and adolescence increases risk for chronic pain in adulthood

A few studies of long-term outcomes for pediatric functional abdominal pain (FAP) have assessed acute non-abdominal pain at follow-up, but none has assessed chronic pain. We followed a cohort of pediatric patients with FAP (n=155) and a well control group (n=45) prospectively for up to 15 years. Participants ranged in age from 18 to 32 years at a follow-up telephone interview. FAP patients were classified as Resolved (n=101) versus Unresolved (n=54) at follow-up, based on whether they reported symptoms consistent with the adult Rome III criteria for a functional gastrointestinal disorder. Headache symptoms and reports of chronic non-abdominal pain also were assessed at follow-up. In the Unresolved group, 48.1% reported one or more sites of chronic non-abdominal pain at follow-up, compared to 24.7% in the Resolved group and 13.3% in the control group, p<0.01. More than half (57.4%) of the Unresolved group endorsed symptoms consistent with International Headache Society criteria for headache, compared to 44.6% of the Resolved group and 31% of controls, p<0.05. One-third of the Unresolved group reported both headache and one or more sites of chronic non-abdominal pain at follow-up, compared to 17.8% of the Resolved group and 4.4% of controls. Youth with FAP that persists into adulthood may be at increased risk for chronic pain and headache. Examination of central mechanisms that are common across chronic pain disorders may enhance understanding of this subgroup of FAP.

Repeated psychological stress-induced alterations of visceral sensitivity and colonic motor functions in mice: influence of surgery and postoperative single housing on visceromotor responses

Visceral pain modulation by chronic stress in mice has been little studied. Electromyography (EMG) recording of abdominal muscle contractions, as a proxy to the visceromotor response (VMR), requires electrode implantation and post-surgical single housing (SH) which could affect the VMR to stress. To test this hypothesis, male mice had electrode implantation surgery (S) plus SH, or no surgery and were group housed (NS-GH) or single housed (NS-SH) and exposed to either water avoidance stress (WAS, 1 h/day) or left undisturbed in their home cages for 10 days. The VMR to phasic ascending colorectal distension (CRD) was assessed before (basal) and 24 h after 10 days of WAS or no stress using a surgery-free method of intraluminal colonic pressure (ICP) recording (solid-state manometry). WAS heightened significantly the VMR to CRD at 30, 45, and 60 mmHg in S-SH vs. NS-GH, but not compared to NS-SH conscious mice. Compared to basal CRD, WAS increased VMR at 60 mmHg in the S-SH group and decreased it at 30-60 mmHg in NS-GH mice, while having no effect in NS-SH mice. The average defecation during the hour of repeated WAS over 10 days was 1.9 and 2.4 fold greater in S-SH vs. NS-GH and NS-SH mice, respectively. These data indicate that the combination of S-SH required for VMR monitoring with EMG is an important component of repeated WAS-induced post-stress visceral hypersensitivity and defecation in mice.

Hydrogen sulphide induces micro opioid receptor-dependent analgesia in a rodent model of visceral pain

BACKGROUND

Hydrogen sulphide (H2S) is a gaseous neuro-mediator that exerts analgesic effects in rodent models of visceral pain by activating KATP channels. A body of evidence support the notion that KATP channels interact with endogenous opioids. Whether H2S-induced analgesia involves opioid receptors is unknown.

METHODS

The perception of painful sensation induced by colorectal distension (CRD) in conscious rats was measured by assessing the abdominal withdrawal reflex. The contribution of opioid receptors to H2S-induced analgesia was investigated by administering rats with selective mu, kappa and delta opioid receptor antagonists and antisenses. To investigate whether H2S causes mu opioid receptor (MOR) transactivation, the neuronal like cells SKNMCs were challenged with H2S in the presence of MOR agonist (DAMGO) or antagonist (CTAP). MOR activation and phosphorylation, its association to beta arrestin and internalization were measured.

RESULTS

H2S exerted a potent analgesic effects on CRD-induced pain. H2S-induced analgesia required the activation of the opioid system. By pharmacological and molecular analyses, a robust inhibition of H2S-induced analgesia was observed in response to central administration of CTAP and MOR antisense, while kappa and delta receptors were less involved. H2S caused MOR transactivation and internalization in SKNMCs by a mechanism that required AKT phosphorylation. MOR transactivation was inhibited by LY294002, a PI3K inhibitor, and glibenclamide, a KATP channels blocker.

CONCLUSIONS

This study provides pharmacological and molecular evidence that antinociception exerted by H2S in a rodent model of visceral pain is modulated by the transactivation of MOR. This observation provides support for development of new pharmacological approaches to visceral pain.

Serotonin transporter expression in rats with chronic visceral hypersensitivity

AIM: To determine whether colonic serotonin transporter (SERT) expression is altered in rats with visceral hypersensitivity and to explore the possible mechanism underlying the pathogenesis of visceral hypersensitivity.

METHODS: A rat model of visceral hypersensitivity was created by intracolonic injection of acetic acid between postnatal days 8 and 21. The expression of SERT mRNA and protein in the colonic epithelium was detected by RT-PCR and immunohistochemistry, respectively. The levels of serotonin in plasma and colonic tissue were also measured.

RESULTS: Colon irritation in neonates resulted in chronic visceral hypersensitivity in the absence of identifiable peripheral pathology. Under different capacities the abdominal withdrawal reflex (AWR) score in rats with chronic visceral hypersensitivity was significantly higher than that in controls (P < 0.01). Although plasma serotonin content significantly increased in rats with visceral hypersensitivity compared to controls (95.75 ± 15.99 vs 72.17 ± 8.01, P < 0.01), no significant difference was noted in colonic serotonin content between the two groups. SERT immunoreactivity in colonic epithelium was significantly reduced in rats with visceral hypersensitivity (0.187 ± 0.010 vs 0.191 ± 0.011, P < 0.01), whereas a significant increase was noted in SERT mRNA level in the colon of rats with visceral hypersensitivity compared to controls (16.02 ± 3.7 vs 9.47 ± 2.34, P < 0.05).

CONCLUSION: In visceral hypersensitivity, the increase in serotonin content is mainly due to decreased degradation of the protein. The expression and function of SERT may be different in serotonergic neurons compared to colonic epithelial mucosa cells.

Role of spinal cord glia in the central processing of peripheral pain perception

BACKGROUND

The discovery that glial activation plays a critical role in the modulation of neuronal functions and affects the spinal processing of nociceptive signalling has brought new understanding on the mechanisms underlying central sensitization involved in chronic pain facilitation. Spinal glial activation is now considered an important component in the development and maintenance of allodynia and hyperalgesia in various models of chronic pain, including neuropathic pain and pain associated with peripheral inflammation. In addition, spinal glial activation is also involved in some forms of visceral hyperalgesia.

PURPOSE

We discuss the signalling pathways engaged in central glial activation, including stress pathways, and the neuron-glia bidirectional relationships involved in the modulation of synaptic activity and pain facilitation. In this expanding field of research, the characterization of the mechanisms by which glia affect spinal neuro-transmission will increase our understanding of central pain facilitation, and has the potential for the development of new therapeutic agents for common chronic pain conditions.

Role of oxidative stress in animal model of visceral pain

Reactive oxygen species play an important role both in physiological and pathophysiological reactions. The aim of this study was to determine the role of free radicals and antioxidants in the development of visceral pain. Visceral pain was produced by colorectal distension (CRD) in adult rats. CRD was caused by insertion of a lubricated latex balloon into the descending colon and rectum followed by inflation to 80mm Hg for 10min. During CRD, visceral pain was rated on 0-3.5 point scale. Oxidative stress was determined indirectly by measurement of free radical scavenging enzymes (glutathione peroxidase (GPx) and superoxide dismutase (SOD)) in the blood, liver and brain. Following CRD we observed (1) all rats expressed signs of visceral pain (overall rating was 1.83), (2) SOD and GPx levels were increased in the liver and blood, and decreased in the brain samples and (3) administration of the antioxidant Trolox, a water-soluble derivate of vitamin E, prior to CRD, prevented SOD and GPx changes in the liver, blood and brain, but did not affect pain scores. It was concluded, that CRD as a model of visceral pain, increases oxidative stress in animals, which could be prevented by prior administration of antioxidants; however, antioxidants did not attenuate signs of visceral pain caused by CRD.

Effectiveness of trimebutine maleate on modulating intestinal hypercontractility in a mouse model of postinfectious irritable bowel syndrome

Trimebutine maleate, which modulates the calcium and potassium channels, relieves abdominal pain in patients with irritable bowel syndrome. However, its effect on postinfectious irritable bowel syndrome is not clarified. The aim of this study was to investigate the effectiveness of trimebutine maleate on modulating colonic hypercontractility in a mouse model of postinfectious irritable bowel syndrome. Mice infected up to 8 weeks with T. spiralis underwent abdominal withdrawal reflex to colorectal distention to evaluate the visceral sensitivity at different time points. Tissues were examined for histopathology scores. Colonic longitudinal muscle strips were prepared in the organ bath under basal condition or to be stimulated by acetylcholine and potassium chloride, and consecutive concentrations of trimebutine maleate were added to the bath to record the strip responses. Significant inflammation was observed in the intestines of the mice infected 2 weeks, and it resolved in 8 weeks after infection. Visceral hyperalgesia and colonic muscle hypercontractility emerged after infection, and trimebutine maleate could effectively reduce the colonic hyperreactivity. Hypercontractility of the colonic muscle stimulated by acetylcholine and high K(+) could be inhibited by trimebutine maleate in solution with Ca(2+), but not in Ca(2+) free solution. Compared with 8-week postinfectious irritable bowel syndrome group, 2-week acute infected strips were much more sensitive to the stimulators and the drug trimebutine maleate. Trimebutine maleate was effective in reducing the colonic muscle hypercontractility of postinfectious irritable bowel syndrome mice. The findings may provide evidence for trimebutine maleate to treat postinfectious irritable bowel syndrome patients effectively.

Long-term impact of neonatal injury in male and female rats: Sex differences, mechanisms and clinical implications

Over the last several decades, the relative contribution of early life events to individual disease susceptibility has been explored extensively. Only fairly recently, however, has it become evident that abnormal or excessive nociceptive activity experienced during the perinatal period may permanently alter the normal development of the CNS and influence future responses to somatosensory input. Given the significant rise in the number of premature infants receiving high-technology intensive care over the last 20 years, ex-preterm neonates may be exceedingly vulnerable to the long-term effects of repeated invasive interventions. The present review summarizes available clinical and laboratory findings on the lasting impact of exposure to noxious stimulation during early development, with a focus on the structural and functional alterations in nociceptive circuits, and its sexually dimorphic impact.

Transient receptor potential vanilloid-1 (TRPV1) and ankyrin-1 (TRPA1) participate in visceral hyperalgesia in chronic water avoidance stress rat model

Stressfull life events have powerful influences on visceral perception of certain IBS patients. In the present study, we aimed to examine the involvement of TRPV1 and TRPA1 in the stress-induced visceral hyperalgesia. Rats were exposed to 1-h water avoidance stress (WAS) daily for 10 consecutive days. The abdominal withdrawal reflex (AWR) to colorectal distension was assessed at the end of the 10-day period. Western-blotting analysis was applied to investigate the alterations of TRPV1 and TRPA1 in the colonic afferent dorsal root ganglia (DRG). Compared with control rats, the WAS-treated rats demonstrated a significant increase in the AWR with the pressure > or = 40 mm Hg (P < 0.05). Meanwhile, in the WAS-treated rats, western-blotting analysis showed significant upregulation of TRPV1 and TRPA1 in the colonic afferent DRG. The results indicate that WAS could induce the upregulation of TRPV1 and TRPA1 in the colonic afferent DRG, and both receptors may be candidate molecules involved in the stress-induced visceral hyperalgesia in rats.

Analgesic effects of JCM-16021 on neonatal maternal separation-induced visceral pain in rats

AIM: To investigate the pharmacological effect of JCM-16021, a Chinese herbal formula, and its underlying mechanisms.

METHODS: JCM-16021 is composed of seven herbal plant materials. All raw materials of the formula were examined according to the quality control criteria listed in the Chinese Pharmacopeia (2005). In a neonatal maternal separation (NMS) model, male Sprague-Dawley rats were submitted to daily maternal separation from postnatal day 2 to day 14, or no specific handling (NH). Starting from postnatal day 60, rats were administered JCM-16021 (2, 4, 8 g/kg per day) orally twice a day for 28 d. Pain threshold pressure and electromyographic activities of external oblique muscles in response to colorectal distention recorded with a Power Lab System (AD Instruments International), were tested as pain indices. Changes in serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations in the colon of rats were analyzed; the enterochromaffin cell numbers and serotonin transporter in the colon of rats were also evaluated with an immunohistochemistry method.

RESULTS: NMS treatment significantly reduced pain threshold pressure (37.4 ± 1.4 mmHg), as compared to that of NH rats (57.7 ± 1.9 mmHg, P < 0.05). After JCM-16021 treatment, the pain threshold pressure significantly increased when compared to that before treatment (34.2 ± 0.9 mmHg vs 52.8 ± 2.3 mmHg in the high dose group, 40.2 ± 1.6 mmHg vs 46.5 ± 1.3 mmHg in the middle dose group, and 39.3 ± 0.7 mmHg vs 46.5 ± 1.6 mmHg in the low dose group, P < 0.05). Also JCM-16021 significantly and dose-dependently decreased electromyographic activity to the graded colorectal distension (CRD), (the mean ΔAUC values were: 0.17 ± 0.03, 0.53 ± 0.15, 1.06 ± 0.18, 1.22 ± 0.24 in the high dose group; 0.23 ± 0.04, 0.68 ± 0.17, 1.27 ± 0.26, 1.8 ± 0.3 in the middle dose group; and 0.29 ± 0.06, 0.8 ± 0.16, 1.53 ± 0.24, 2.1 ± 0.21 in the low dose group for the pressures 20, 40, 60, 80 mmHg), as compared to the NMS vehicle group. The mean ΔAUC values were: 0.57 ± 0.12, 1.33 ± 0.18, 2.57 ± 0.37, 3.08 ± 0.37 for the pressures 20, 40, 60, 80 mmHg (P < 0.05). JCM-16021 treatment significantly reduced the 5-HT concentrations (from high, middle and low dosage groups: 60.25 ± 5.98 ng/100 mg, 60.32 ± 4.22 ng/100 mg, 73.31 ± 7.65 ng/100 mg), as compared to the NMS vehicle groups (93.11 ± 9.85 ng/100 mg, P < 0.05); and increased the 5-HIAA concentrations (after treatment, from high, middle and low dosage groups: 54.24 ± 3.27 ng/100 mg, 50.34 ± 1.26 ng/100 mg, 51.37 ± 2.13 ng/100 mg) when compared to that in the NMS vehicle group (51.75 ± 1.98 ng/100 mg, P < 0.05); but did not change the enterochromaffin cell numbers in the colon of rats. In addition, NMS rats had higher SERT expression (n = 10) than NH rats (n = 8, P < 0.05). JCM-16021 treatment significantly decreased SERT expression when compared to the NMS group (P < 0.01-0.001).

CONCLUSION: JCM-16021 can attenuate visceral hypersensitivity, and this analgesic effect may be mediated through the serotonin signaling pathway in the colon of rats.

Neonatal bladder inflammation alters activity of adult rat spinal visceral nociceptive neurons

PURPOSE

This investigation examined the effect of inflammation produced by intravesical zymosan during the neonatal period on spinal dorsal horn neuronal responses to urinary bladder distension (UBD) as adults.

METHODS

Female rat pups (P14-P16) were treated with intravesical zymosan or with anesthesia-only. These groups of rats were subdivided forming four groups: half received intravesical zymosan as adults and half received anesthesia-only. One day later, rats were anesthetized, the spinal cord was transected at a cervical level and extracellular single-unit recordings of L6-S1 dorsal horn neurons were obtained. Neurons were classified as Type I--inhibited by heterotopic noxious conditioning stimuli (HNCS) or as Type II--not inhibited by HNCS--and were characterized for Spontaneous Activity and responses to graded UBD (20-60 mm Hg).

RESULTS

227 spinal dorsal horn neurons excited by UBD were characterized. In rats treated as neonates with anesthesia-only, Type II neurons demonstrated increased spontaneous and UBD-evoked activity following adult intravesical zymosan treatment whereas Type I neurons demonstrated decreased spontaneous and UBD-evoked activity relative to controls. In rats treated as neonates with intravesical zymosan, the spontaneous and UBD-evoked activity of both Type I and Type II neurons increased following adult intravesical zymosan treatment relative to controls.

CONCLUSIONS

Neonatal bladder inflammation alters subsequent effects of acute bladder inflammation on spinal dorsal horn neurons excited by UBD such that overall there is greater sensory neuron activation. This may explain the visceral hypersensitivity noted in this model system and suggest that impaired inhibitory systems may be responsible.

Hypoalgesia related to elevated resting blood pressure is absent in adolescents and young adults with a history of functional abdominal pain

Elevated resting blood pressure (BP) is hypoalgesic in healthy individuals, but this effect is absent in adults with chronic somatic pain. This study tested whether BP-related hypoalgesia is similarly altered in individuals with a history of chronic visceral pain in childhood. Resting BP was assessed in 94 adolescents and young adults with a known history of childhood functional abdominal pain (FAP) and 55 comparable healthy controls. Responses to an acute heat pain stimulus were then evaluated following exposure to two laboratory stressors. A significant participant type x systolic BP (SBP) interaction (p<.005) revealed that elevated resting SBP was associated with significantly higher heat pain threshold (p<.001) in healthy controls, but was unrelated to pain threshold in the FAP group. A similar pattern was observed for heat pain tolerance, with elevated SBP linked to significantly higher pain tolerance (p<.05) in healthy controls, but unrelated to tolerance in the FAP group. Dysfunction in BP-related hypoalgesia associated with FAP was evident regardless of whether childhood FAP had resolved or still persisted at the time of laboratory testing. Subgroup analyses indicated that BP-related hypoalgesia (in healthy controls) and FAP-linked absence of this hypoalgesia was observed only among females. Result suggest that childhood visceral chronic pain may be associated with relatively long-lasting dysfunction in overlapping systems modulating pain and BP that persists even after FAP resolves. Potential implications for later hypertension risk are discussed.

Expression of CD11c, VIP and IL-1β in the intestine and peripheral blood of rats with intestinal dysfunction induced by cold-restraint stress

AIM: To investigate the expression of CD11c, vasoactive intestinal peptide (VIP) and interleukin-1β (IL-1β) in the intestine and peripheral blood of rats with intestinal dysfunction induced by cold-restraint stress, and analyze the changes in intestinal immune tolerance in these rats.

METHODS: Sixty Wistar rats were randomly divided into control group and experimental group. Intestinal dysfunction was induced in rats by cold-restraint stress. The macroscopic and histological changes in the terminal ileum and distal colon were scored. Immunohistochemistry was used to detect the expression of CD11c, VIP and IL-1β in the intestine. The levels of VIP and IL-1β in peripheral blood was measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS: Although there was no significant difference in the expression of CD11c in the terminal ileum between the experimental group and the control group, the expression levels of VIP and IL-1β in the terminal ileum in the experimental group were significantly higher than those in the control group (177.67 ± 35.44 vs 92.64 ± 22.19, and 359.56 ± 45.48 vs 216.46 ± 41.56, respectively; both P < 0.05). A positive linear correlation was noted between the expression of VIP and IL-1β in the terminal ileum (r = 0.78, P < 0.01). No significant differences were noted in the expression levels of CD11c and IL-1β in the distal colon between the experimental group and control group, whereas the expression level of VIP in the experimental group was significantly higher than that in the control group (380.15 ± 33.24 vs 254.04 ± 40.53, P < 0.05). Compared with the control group, the levels of VIP and IL-1β in peripheral blood increased significantly in the experimental group (149.03 ± 56.82 ng/L vs 104.24 ± 39.03 ng/L, and 8.82 ± 3.91 ng/L vs 5.49 ± 3.79 ng/L, respectively; both P < 0.05).

CONCLUSION: Low-grade inflammation is noted in the terminal ileum and distal colon of rats with intestinal dysfunction induced by cold-restraint stress. Dentritic cells may not be involved in the pathogenesis of mild intestinal inflammation response present in the bowel of rats with intestinal dysfunction.

Intestinal membrane permeability and hypersensitivity in the irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder in which the underlying pathophysiology is poorly understood; however, increased intestinal permeability in diarrhea-predominant IBS patients has been reported. Here we demonstrate that diarrhea-predominant IBS (D-IBS) patients display increased intestinal permeability. We have also found that increased intestinal membrane permeability is associated with visceral and thermal hypersensitivity in this subset of D-IBS patients. We evaluated 54 D-IBS patients and 22 controls for intestinal membrane permeability using the lactulose/mannitol method. All subjects ingested 5g of lactulose and 2g of mannitol in 100ml of water after which their urine was collected. We also evaluated the mean mechanical visual analogue scale (M-VAS) pain rating to nociceptive thermal and visceral stimulation in all subjects. All study participants also completed the FBDSI scale. Approximately 39% of diarrhea-predominant IBS patients had increased intestinal membrane permeability as measured by the lactulose/mannitol ratio. These IBS patients also demonstrated higher M-VAS pain intensity reading scale. Interestingly, the IBS patients with hypersensitivity and increased intestinal permeability had a higher FBDSI score (100.8 + or - 5.4) than IBS patients with normal membrane permeability and sensitivity (51.6 + or - 12.7) and controls (6.1 + or - 5.6) (p<0.001). A subset of D-IBS patients had increased intestinal membrane permeability that was associated with an increased FBDSI score and increased hypersensitivity to visceral and thermal nociceptive pain stimuli. Thus, increased intestinal membrane permeability in D-IBS patients may lead to more severe IBS symptoms and hypersensitivity to somatic and visceral stimuli.

Neonatal bladder inflammation produces functional changes and alters neuropeptide content in bladders of adult female rats

Neonatal bladder inflammation has been demonstrated to produce hypersensitivity to bladder re-inflammation as an adult. The purpose of this study was to investigate the effects of neonatal urinary bladder inflammation on adult bladder function and structure. Female Sprague-Dawley rats were treated on postnatal days 14 to 16 with intravesical zymosan or anesthesia alone. At 12 to 16 weeks of age, micturition frequency and cystometrograms were measured. Similarly treated rats had their bladders removed for measurement of plasma extravasation after intravesical mustard oil, for neuropeptide analysis (calcitonin gene-related peptide or Substance P) or for detailed histological examination. Rats treated with zymosan as neonates exhibited increased micturition frequency, reduced micturition volume thresholds, greater extravasation of Evans blue after intravesical mustard oil administration, and greater total bladder content of calcitonin gene-related peptide and Substance P. In contrast, there were no quantitative histological changes in the thickness, fibrosis, or mast cells of bladder tissue due to neonatal zymosan treatments. Functional changes in urologic systems observed in adulthood, coupled with the increased neuropeptide content and neurogenic plasma extravasation in adult bladders, suggest that the neonatal bladder inflammation treatment enhanced the number, function, and/or neurochemical content of primary afferent neurons. These data support the hypothesis that insults to the urologic system in infancy may contribute to the development of adult bladder hypersensitivity.

PERSPECTIVE

Inflammation of the bladder early in life in the rat has multiple sequelae, including laboratory measures that suggest an alteration of the neurophysiological substrates related to the bladder. Some painful bladder syndromes in humans have similar characteristics and so may be due to similar mechanisms.

Effect of electro-acupuncture on substance P, its receptor and corticotropin-releasing hormone in rats with irritable bowel syndrome

AIM: To investigate the effect and mechanism of electro-acupuncture (EA) at ST25 and ST37 on irritable bowel syndrome (IBS) of rats.

METHODS: A total of 21 male Sprague-Dawley rats were randomly divided into normal group, model group and EA group. A rat model of IBS was established by constraining the limbs and distending the colorectum of rats. Rats in EA group received bilateral EA at ST25 and ST37 with a sparse and intense waveform at a frequency of 2/50 Hz for 15 min, once a day for 7 d as a course. Rats in normal and model groups were stimulated by distending colorectum (CR). An abdominal withdrawal reflex (AWR) scoring system was used to evaluate improvements in visceral hypersensitivity. Toluidine blue-improved method, immunohistochemistry and radioimmunoassay were used to observe mucosal mast cells (MC), changes of substance P (SP) and substance P receptor (SPR) in colon and change of corticotropin-releasing hormone (CRH) in hypothalamus.

RESULTS: The threshold of visceral sense was significantly lower in model group than in normal group, and significantly higher in EA group than in model group. The number of mucosal MC was greater in model group than in normal group and significantly smaller in EA group than in model group. The CRH level in hypothalamus of rats was significantly higher in model group than in normal group, which was remarkably decreased after electro-acupuncture treatment. The SP and SPR expression in colon of rats in model group was decreased after electro-acupuncture treatment.

CONCLUSION: EA at ST25 and ST37 can decrease the number of mucosal MC and down-regulate the expression of CRH in hypothalamus, and the expression of SP and SPR in colon of rats with IBS.

Acupuncture at both ST25 and ST37 improves the pain threshold of chronic visceral hypersensitivity rats

Previous studies demonstrated the efficacy of electro-acupuncture (EA) in relieving chronic visceral hypersensitivity (CVH) in IBS rats. However, ST25 which is a key acupoint for patients with IBS has not been reported in these experiments. Eight CVH rats were treated by EA at both ST25 and ST37 for 20 min, once daily for seven consecutive days, model rats (n = 8) and normal rats (n = 8) as controls. After the first EA treatment, the abdominal withdrawal reflex scores were investigated to evaluate the pain threshold. After seven EA treatments, the concentrations of 5-hydroxytryptamine (5-HT), 5-HT3 receptor (5-HT3R) and 5-HT4 receptor (5-HT4R) in colon tissue were assayed quantitatively by enzyme-linked immunosorbent assay. The results showed that EA improved the pain threshold of CVH rats, reduced the 5-HT concentration and increased the 5-HT4R concentration, but had no effect on the 5-HT3R concentration. Further studies are needed to optimize the choice of two-matching points for EA in the treatment of CVH rats.

Visceral pain: the neurophysiological mechanism

The mechanism of visceral pain is still less understood compared with that of somatic pain. This is primarily due to the diverse nature of visceral pain compounded by multiple factors such as sexual dimorphism, psychological stress, genetic trait, and the nature of predisposed disease. Due to multiple contributing factors there is an enormous challenge to develop animal models that ideally mimic the exact disease condition. In spite of that, it is well recognized that visceral hypersensitivity can occur due to (1) sensitization of primary sensory afferents innervating the viscera, (2) hyperexcitability of spinal ascending neurons (central sensitization) receiving synaptic input from the viscera, and (3) dysregulation of descending pathways that modulate spinal nociceptive transmission. Depending on the type of stimulus condition, different neural pathways are involved in chronic pain. In early-life psychological stress such as maternal separation, chronic pain occurs later in life due to dysregulation of the hypothalamic-pituitary-adrenal axis and significant increase in corticotrophin releasing factor (CRF) secretion. In contrast, in early-life inflammatory conditions such as colitis and cystitis, there is dysregulation of the descending opioidergic system that results excessive pain perception (i.e., visceral hyperalgesia). Functional bowel disorders and chronic pelvic pain represent unexplained pain that is not associated with identifiable organic diseases. Often pain overlaps between two organs and approximately 35% of patients with chronic pelvic pain showed significant improvement when treated for functional bowel disorders. Animal studies have documented that two main components such as (1) dichotomy of primary afferent fibers innervating two pelvic organs and (2) common convergence of two afferent fibers onto a spinal dorsal horn are contributing factors for organ-to-organ pain overlap. With reports emerging about the varieties of peptide molecules involved in the pathological conditions of visceral pain, it is expected that better therapy will be achieved relatively soon to manage chronic visceral pain.

Neonatal injury alters adult pain sensitivity by increasing opioid tone in the periaqueductal gray

Studies in both rodents and humans have shown that acute inflammatory pain experienced during the perinatal period produces long-term decreases in pain sensitivity (hypoalgesia) (Grunau et al., 1994a, 2001; Ren et al., 2004; LaPrairie and Murphy, 2007). To date, the mechanisms underlying these long-term adaptations, however, have yet to be elucidated. The present studies tested the hypothesis that neonatal inflammatory pain induces an upregulation in endogenous opioid tone that is maintained into adulthood, and that this increase in opioid tone provides the underlying mechanism for the observed hypoalgesia. On the day of birth (P0), inflammatory pain was induced in male and female Sprague-Dawley rats by intraplantar administration of carrageenan (CGN; 1%). In adulthood (P60), these animals displayed significantly increased paw withdrawal latencies in response to a noxious thermal stimulus in comparison to controls. Systemic administration of the brain-penetrant opioid receptor antagonist naloxone HCl, but not the peripherally restricted naloxone methiodide, significantly attenuated the injury-induced hypoalgesia. Direct administration of naloxone HCl or antagonists directed at the mu or delta opioid receptors into the midbrain periaqueductal gray (PAG) also significantly reversed the injury-induced hypoalgesia in adult rats. Parallel anatomical studies revealed that inflammatory pain experienced on the day of birth significantly increased beta-endorphin and met/leu-enkephalin protein levels and decreased opioid receptor expression in the PAG of the adult rat. Thus, early noxious insult produces long-lasting alterations in endogenous opioid tone, thereby profoundly impacting nociceptive responsiveness in adulthood.

Importance of neural mechanisms in colonic mucosal and muscular dysfunction in adult rats following neonatal colonic irritation

Previous studies have shown that early life trauma induced by maternal separation or colonic irritation leads to hypersensitivity to colorectal distension in adulthood. We tested the hypothesis that repetitive colorectal distension in neonates leads to abnormalities in colonic permeability and smooth muscle function in the adult rat. In neonatal rats, repetitive colorectal distension was performed on days 8, 10, and 12. As adults, stool consistency was graded from 0 (formed stool) to 3 (liquid stool). Colonic tissue was isolated for histology and myeloperoxidase levels. The colonic mucosa was placed in modified Ussing chambers for measurements of permeability and short-circuit current responses to forskolin, electrical field stimulation, and carbachol. Segments of colonic musculature were placed in organ baths and contractile response to potassium chloride, electrical field stimulation, and carbachol were determined. In adult rats that experienced neonatal colonic irritation, no significant changes in colonic histology or myeloperoxidase activity were observed; however, stool consistency scores were increased. Mucosal permeability, measured as an increase in basal conductance, was significantly increased but no changes in short-circuit current responses were observed. In adulthood, rats that underwent colorectal distension as neonates exhibited an elevated smooth muscle contractile response to potassium chloride, but no changes in response to electrical field stimulation or carbachol. In summary, neonatal colonic irritation, shown previously to produce colonic hypersensitivity, leads to significant alterations in colonic mucosal and smooth muscle function characterized by loose stools, increased mucosal permeability, and increased smooth muscle contractility in the absence of colon inflammation in adulthood.

Electro-acupuncture relieves visceral sensitivity and decreases hypothalamic corticotropin-releasing hormone levels in a rat model of irritable bowel syndrome

Previous studies into electro-acupuncture (EA) treatment of irritable bowel syndrome (IBS) have principally focused on the peripheral effects of EA in a rat model of IBS. It is not known whether EA exerts central effects in this rat model. We have examined the effects of EA on hypothalamic corticotropin-releasing hormone (CRH) levels in a rat model of IBS provoked by colorectal distension (CRD) and forelimb immobilization. EA was administered once daily to IBS model rats over a period of 7 d; untreated IBS rats and controls were also studied. The behavioral response to distension was rated according to the abdominal withdrawal reflex (AWR) score; hypothalamic CRH levels were measured by radioimmunoassay. We report that EA treatment significantly decreased visceral sensitivity to CRD in this rat model. In treated animals, EA also decreased hypothalamic CRH to control levels. Reduced hypothalamic CRH levels may mediate the beneficial effects of EA in this rat IBS model.

Sensory denervation reduces visceral hypersensitivity in adult rats exposed to chronic unpredictable stress: evidences of neurogenic inflammation

The purpose of this study is to provide evidence of neurogenic inflammation in chronic unpredictable stressed rats with the changes of visceral sensitivity, number of mast cells, and close proximity among mast cell-nerve-blood vessels. We found that (1) capsaicin denervation blocked stress-induced increase of visceral sensitivity, while doxantrazole presented a partial blocking; (2) capsaicin denervation blocked stress-induced enhancement of the proximity of mast cell-nerve fiber-blood vessels and blood vessel damage, while doxantrazole showed no effects on these; (3) doxantrazole blocked stress-induced increases of the MPO activity, the number and the degranulation of mast cells in the colon; (4) sensory denervation and doxantrazole had no effects on stress-induced behavioral inhibition. These results suggest that capsaicin-sensitive sensory fibers play a key role in stress-induced visceral hypersensitivity and the ultrastructural changes, mast cells play an important role in the generation of stress-induced colon inflammation.

NADPH-d/NOS reactivity in the lumbar dorsal horn of congenitally hypothyroid pups before and after formalin pain induction

We have previously demonstrated that congenitally hypothyroid rat pups exhibit altered behavioral response to formalin pain induction during postnatal period. In the present study, using NADPH-diaphorase histochemistry and NOS immunostaining, we investigated the effect of congenital hypothyroidism on the NOS expression in spinal cord of intact neonates at postnatal days of 15 and 21. We also examined the effect of thyroid dysfunction on the NADPH-d/NOS expression in response to formalin nociception. Congenital hypothyroidism induced by propylthiouracil (PTU) treatment started from gestational day 16 and continued to postnatal day 15 or 21. Congenitally hypothyroid pups exhibited marked reduction in NADPH-d reactive cells (84% and 66% in P15 and P21, respectively; P<0.001) and NOS-ir cells (52% and 91% in P15 and P21, respectively; P<0.001) in superficial lumbar dorsal horn laminae (I-II) as compared to that of normal pups. Moreover, in congenitally hypothyroid pups the NADPH-d/NOS expression following hindpaw formalin injection did not change significantly. Our results demonstrate that congenital hypothyroidism affect developmental expression of NOS in spinal dorsal horn, which may in part explain the altered behavioral pain response as we previously reported in hypothyroid pups.

The endogenous hydrogen sulfide producing enzyme cystathionine-beta synthase contributes to visceral hypersensitivity in a rat model of irritable bowel syndrome

Background

The pathogenesis of visceral hypersensitivity, a characteristic pathophysiological feature of irritable bowel syndrome (IBS), remains elusive. Recent studies suggest a role for hydrogen sulfide (H₂S) in pain signaling but this has not been well studied in visceral models of hyperalgesia. We therefore determined the role for the endogenous H₂S producing enzyme cystathionine-β-synthetase (CBS) in a validated rat model of IBS-like chronic visceral hyperalgesia (CVH). CVH was induced by colonic injection of 0.5% acetic acid (AA) in 10-day-old rats and experiments were performed at 8–10 weeks of age. Dorsal root ganglion (DRG) neurons innervating the colon were labeled by injection of DiI (1,1'-dioleyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate) into the colon wall.

Results

In rat DRG, CBS-immunoreactivity was observed in approximately 85% of predominantly small- and medium-sized neurons. Colon specific DRG neurons revealed by retrograde labeling DiI were all CBS-positive. CBS-positive colon neurons co-expressed TRPV1 or P2X3 receptors. Western blotting analysis showed that CBS expression was significantly increased in colon DRGs 8 weeks after neonatal AA-treatment. Furthermore, the CBS inhibitor hydroxylamine markedly attenuated the abdominal withdrawal reflex scores in response to colorectal distention in rats with CVH. By contrast, the H₂S donor NaHS significantly enhanced the frequency of action potentials of colon specific DRG neurons evoked by 2 times rheobase electrical stimulation.

Conclusion

Our results suggest that upregulation of CBS expression in colonic DRG neurons and H₂S signaling may play an important role in developing CVH, thus identifying a specific neurobiological target for the treatment of CVH in functional bowel syndromes.

Voltage-gated potassium channels in IB4-positive colonic sensory neurons mediate visceral hypersensitivity in the rat

OBJECTIVES

Irritable bowel syndrome (IBS) is associated with a state of chronic visceral hypersensitivity, but the underlying molecular mechanisms of visceral hyperalgesia remain elusive. This study was designed to examine changes in the excitability and alterations of voltage-gated K+ currents in subpopulations of colonic dorsal root ganglion (DRG) neurons in a rat model of IBS-like visceral hypersensitivity.

METHODS

The model of IBS-like visceral hypersensitivity was induced by intracolonic infusion of 0.5% acetic acid (AA) in saline from postnatal days 8 -21. Experiments were conducted when rats became adults. DRG neurons innervating the colon were identified by 1,1'-dioleoyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate (DiI) fluorescence labeling and were immunostained for isolectin B4 (IB4) binding to classify these colonic neurons. Patch-clamp recordings were made from acutely dissociated DiI-labeled DRG neurons, and the expression of K+ channel in L6-S2 DRG was examined by reverse transcription-polymerase chain reaction (RT-PCR) and western blot.

RESULTS

(1) Neonatal AA treatment induced long-lasting visceral hypersensitivity without significant inflammation but with mast cell hyperplasia. (2) Colonic DRG neurons contained IB4-positive and negative neurons with different electrophysiological properties. IB4-positive colonic neurons have longer action potentials (APs) and larger A-type K+ currents (I(A)) than the IB4-negative neurons, and IB4 phenotypic changes of colonic neurons were not involved in the chronic visceral hypersensitivity. (3) Neonatal AA treatment decreased I(A) density and changed the electrophysiological properties of I(A) and I(K) by shifting the steady-state inactivation toward a negative direction in IB4-positive colonic neurons. The excitability of these cells increased. (4) Kv4.3 was downregulated in neonatal AA-treated rats compared with control rats, which suggests a possible mechanism regarding the changes in electrical activity of DRG neurons in these rats.

CONCLUSIONS

A new model for chronic visceral hypersensitivity following a diluted AA stimulus in the neonatal period is described. The hypersensitivity may be associated with mast cell hyperplasia in the colon and increased excitability of IB4-positive colonic neurons as a result of suppression of I(A) density and a shift in the inactivation curves of I(A) and I(K) in a hyperpolarizing direction in these cells. This study identifies for the first time a specific molecular mechanism in subpopulations of colonic DRG neurons that underlies chronic visceral hypersensitivity.

The alleviating pain effect of aqueous extract from tong-xie-yao-fang, on experimental visceral hypersensitivity and its mechanism

Tong-Xie-Yao-Fang (TXYF) is a prescription in traditional chinese medicine (TCM), used for relieving abdominal pain associated with irritable bowel syndrome. The aim of the present study was to investigate the effects and mechanism of TXYF on experimental visceral hypersensitivity (VH) models. TXYF affected the abdominal withdrawal reflex produced by colonic distention in maternal separation-induced visceral hypersensitivity rats, in a dosage-dependent manner. TXYF significantly decreased serotonin (5-HT) levels in serum and corticotrophin releasing factor (CRF) concentrations in the brain. Moreover, it was found that VH alleviation by TXYF was dependent on the substance P (SP) expression in the colon mucosa. These results suggest that TXYF attenuates behavioral hyperalgesia by regulating substance associated with the brain-gut axis, including decreasing the expression of 5-HT and SP in the periphery and that of CRF in the center.

Role of anxiety in the pathophysiology of irritable bowel syndrome: importance of the amygdala

A common characteristic of irritable bowel syndrome (IBS) is that symptoms, including abdominal pain and abnormal bowel habits, are often triggered or exacerbated during periods of stress and anxiety. However, the impact of anxiety and affective disorders on the gastrointestinal (GI) tract is poorly understood and may in part explain the lack of effective therapeutic approaches to treat IBS. The amygdala is an important structure for regulating anxiety with the central nucleus of the amygdala facilitating the activation of the hypothalamic-pituitary-adrenal axis and the autonomic nervous system in response to stress. Moreover, chronic stress enhances function of the amygdala and promotes neural plasticity throughout the amygdaloid complex. This review outlines the latest findings obtained from human studies and animal models related to the role of the emotional brain in the regulation of enteric function, specifically how increasing the gain of the amygdala to induce anxiety-like behavior using corticosterone or chronic stress increases responsiveness to both visceral and somatic stimuli in rodents. A focus of the review is the relative importance of mineralocorticoid receptor and glucocorticoid receptor-mediated mechanisms within the amygdala in the regulation of anxiety and nociceptive behaviors that are characteristic features of IBS. This review also discusses several outstanding questions important for future research on the role of the amygdala in the generation of abnormal GI function that may lead to potential targets for new therapies to treat functional bowel disorders such as IBS.

A butyrate-induced model of non-inflammatory colonic hypersensitivity in rats

AIM: To investigate Butyrate-enema's efficacy on visceral hypersensitivity in rats and to explore a new method of establishing a model of non-inflammatory colonic hypersensitivity in rats.

METHODS: Rats of the model group received enemas of 1 mL of butyrate solution (300 mmol/L) twice a day for 6 d. After 3 d or 6 d when the model of visceral hypersensitivity was built, scores of abdominal withdrawal reflex (AWR) in colorectal distention (CRD) were recorded. Hypersensitivity parameters were determined. Meanwhile, the pressure thresholds of initial sensation and most endurance thresholds were recorded. Macroscopic and histologic activities of MPO and counting of mast leukocyte and eosinophile granulocyte were performed on colonic mucosa tissue at the end of the experiment.

RESULTS: Macroscopic and histologic activities of MPO analyses, counting of mast leukocyte and eosinophile granulocyte were not significantly different between control group and experimental group. At day 6, there was a significant increase in scores of CRD in experimental group against control group for the most pressure (t = 9.25, P < 0.01). There were a significant increase in average and highest pressure of colorectal motion in experimental group against control group (t = 36.71, 15.02, both P < 0.01).

CONCLUSION: Butyrate-enema may lead to colonic hypersensitivity while not bring damages to colonic mucosal structure. Colonic hypersensitivity has no correlation with mast cells.

Ice water testing reveals hypersensitivity in adult rats that experienced neonatal bladder inflammation: implications for painful bladder syndrome/interstitial cystitis

PURPOSE

We determined whether clinical observations of hypersensitivity to ice water testing, that is infusion of ice-cold saline into the bladder, in patients with painful bladder syndrome/interstitial cystitis have a parallel in a rat model of bladder hypersensitivity produced by neonatal inflammation.

MATERIALS AND METHODS

Rat pups were anesthetized as neonates (postnatal days 14 to 16). In some pups the bladder was inflamed by intravesical zymosan treatment. As adults, the rats were re-anesthetized and tested for abdominal muscle contractions to ice water testing, measured on electromyogram. Various neonatally treated groups of rats underwent bladder re-inflammation/no re-inflammation and/or bladder distention before ice water testing. Other control rats were treated only in adulthood.

RESULTS

Rats that underwent bladder inflammation as neonates manifested bladder hypersensitivity in adulthood, as indexed by significantly greater mean electromyogram responses during ice water testing. This bladder hypersensitivity did not require adult re-inflammation to manifest. Hypersensitivity was also observed with or without prior bladder distention, although the magnitude of electromyogram responses during ice water testing significantly correlated with the magnitude of electromyogram responses to bladder distention. Neonatally induced effects were not significantly related to estrous cycle phase. Exposure to menthol did not significantly enhance the overall magnitude of the electromyogram response to ice water testing in neonatally treated rats.

CONCLUSIONS

Current results parallel those in a recent study showing that most patients with painful bladder syndrome/interstitial cystitis experience pain when undergoing ice water testing after previous urodynamic testing. These findings suggest that this animal model may be useful for understanding the etiology of and treatment for painful bladder syndrome/interstitial cystitis.

Effect of acupuncture with varied intensity on NMDA and SP expression in spinal dorsal horn in rats with gastric distension-induced pain

AIM: To explore the effect of varied intensity acupuncture on pain-ethology scoring and on expression of n-methyl-d-aspartate receptor (NMDA receptor) and substance P (SP) in spinal dorsal horn quasi-pain in rats with pain induced by gastric distension.

METHODS: Fifty healthy male Sprague Dawley rats were randomly assigned to blank, sham operation, model, acupuncture of lighter stimulus intensity at "Zusanli" point and acupuncture of heavier stimulus intensity at "Zusanli" point groups. Gastric distention model was established by applying implanted aerostat in the gastric and filling in gas to 40 mmHg. Acupuncture of lighter and heavier stimulus intensity was applied. Pain-ethology scoring was observed and expression of NMDA receptor and SP was detected using immunohistochemical method.

RESULTS: Compared with sham operation group, pain-ethology scoring and expression of NMDA receptor in spinal dorsal horn of model group were increased significantly (both P < 0.01). After acupuncture, pain-ethology scoring was decreased significantly (11.77 ± 2.16 vs 22.83 ± 1.87, 14.73 ± 2.19 vs 21.73 ± 2.30, both P < 0.01). Compared with model group, expression of NMDA receptor and SP in spinal dorsal horn of the two acupuncture groups was decreased significantly (140.60 ± 21.30 vs 240.20 ± 25.59, 63.60 ± 13.74 vs 108.67 ± 11.37; 63.60 ± 13.74 vs 108.67 ± 11.37, 82.67 ± 12.13 vs 108.67 ± 11.37, all P < 0.01), and acupuncture of lighter stimulus intensity group had more obvious effect.

CONCLUSION: Acupuncture at "Zusanli" could relieve stress reaction induced by gastric distension and decrease pain-ethology scoring, which is related to inhibited expression of pain correlation information substances (NMDA and SP).

Spinal NMDA NR1 subunit expression following transient TNBS colitis

BACKGROUND

N-methyl-D-aspartic acid (NMDA) receptors play an important role in the development of hypersensitivity to visceral and somatic stimuli following inflammation or tissue injury. Our objective was to investigate the role of NMDA NR1 receptors in the spinal cord (T10-L1; L4-S1) of a subset of rats that remain hypersensitive following the histological resolution of TNBS-induced colitis compared to saline treated rats and rats that had recovered both behaviorally and histologically. We hypothesized that NMDA NR1 subunit expression mediates hypersensitivity following transient TNBS colitis.

METHODS

Male Sprague-Dawley rats (150 g-250 g) received 20 mg/rat intracolonic trinitrobenzene sulfonic acid (TNBS) in 50% ethanol or saline. Animals underwent nociceptive visceral/somatic pain testing 16 weeks after resolution of TNBS colitis. Animals were sacrificed and their spinal cords (T10-L1; L4-S1) were retrieved and 2-dimensional polyacrylamide gel electrophoresis and immunohistocytochemistry techniques were used to investigate spinal-NMDA receptor expression.

RESULTS

NR1(001) was the only NMDA NR1 receptor subunit that was expressed in recovered and control rats, whereas hypersensitive animals expressed NR1(011) and NR1(111) as well as NR1(001) subunits. Immunohistochemistry analysis demonstrated increased expression of NMDA NR1-N1, C1, and C2-plus expression in laminae I and II of the spinal cord (T10-L1; L4-S1) in hypersensitive rats but not in recovered/control rats.

CONCLUSIONS

Selective increases in the expression of the NMDA NR1 splice variants occur in hypersensitive rats following resolution of TNBS colitis. This suggests that the NMDA NR1 receptor plays an important role in the development of neuronal plasticity and central sensitization. The recombination of NR1 splice variants may serve as a key functional protein that maintains hypersensitivity following resolution of TNBS colitis.

Synaptic plasticity: the new explanation of visceral hypersensitivity in rats with Trichinella spiralis infection?

BACKGROUND AND AIM

Synaptic plasticity plays an important role in affecting the intensity of visceral reflex. It may also be involved in the development of visceral hypersensitivity. The aim of this study was to investigate the role of synaptic plasticity on visceral hypersensitivity of rats infected by Trichinella spiralis.

METHODS

Thirty male Sprague-Dawley (SD) rats were randomly divided into control, acute, and chronic infection groups, and were investigated at 1 week after adaptive feeding and at 2 and 8 weeks post infection (PI) by oral administration of 1 ml phosphate-buffered saline (PBS) containing 8,000 Trichinella spiralis larvae. Visceral sensitivity was evaluated by electromyography (EMG) recording during colorectal distension. Intestinal inflammation was observed by hematoxylin-eosin (HE) staining. Synaptic ultrastructure parameters, such as postsynaptic density (PSD) length, synaptic cleft, and number of synaptic vesicles, were examined by transmission electron microscopy (TEM). The expression of protein associated with synaptic plasticity, including postsynaptic density-95 (PSD-95), synaptophysin, calbindin-28 K, N-methyl-D-aspartate receptor-1 (NMDA-R1), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPA-R), and glial cell line-derived neurotrophic factor (GDNF), were analyzed by Western blot.

RESULTS

(1) Visceral hypersensitivity was noted in the chronic infection group, although the inflammation was nearly eliminated (P<0.05). Severe inflammation and downregulation of visceral sensitivity were observed in the acute infection group (P<0.05). (2) There were many more synaptic vesicles and longer PSD in the chronic infection group than in the control group (P<0.05, respectively). However, in comparison with control rats, disappearance of mitochondria cristae in the synapses, and decrease of synaptic vesicles and length of PSD were observed in the acute infection group. There was no significant difference in width of synaptic cleft among the three groups. (3) Compared with the control, the expression of proteins associated with synaptic plasticity was significantly upregulated during chronic infection phase (P<0.05), and downregulated during acute infection phase.

CONCLUSION

Synaptic plasticity was observed in SD rats infected by Trichinella spiralis and was associated with visceral sensitivity, which suggests that it may play an important role in the formation of visceral hypersensitivity.