Perceptual responses in patients with inflammatory and functional bowel disease

Lessons Learnt from Post-Infectious IBS

The development of IBS symptoms – altered bowel function and abdominal cramping in a subset of adult subjects exposed to severe enteric infections opened up an unprecedented opportunity to understand the etiology of this poorly understood disorder. Perhaps, for the reasons that these symptoms follow a severe enteric infection, and mucosal biopsy tissues are readily available, the focus of most studies thus far has been to show that mild/low-grade mucosal inflammation persisting after the initial infection has subsided causes the IBS symptoms. Parallel studies in non-infectious IBS patients, who did not have prior enteritis, showed similar mild mucosal inflammation. Together, these studies examined the mucosal infiltration of specific immune cells, increase of select inflammatory mediators, mast cell and enterochromaffin cell hyperplasia, and epithelial permeability. In spite of the fact that the data on these topics were not consistent among different studies and clinical trials with prednisone, fluoxetine, and ketotifen failed to provide relief of IBS symptoms, the predominant conclusions were that mild mucosal inflammation is the cause of IBS symptoms. However, the circular smooth muscle cells, and myenteric neurons are the primary regulators of gut motility function, while primary afferent neurons and CNS play essential roles in induction of visceral hypersensitivity – no explanation was provided as to how mild mucosal inflammation causes dysfunction in cells far removed. Accumulating evidence shows that mild mucosal inflammation in IBS patients is in physiological range. It has little deleterious effects on cells within its own environment and therefore it is unlikely to affect cells in the muscularis externa. This review discusses the disconnect between the focus on mild/low-grade mucosal inflammation and the potential mechanisms and molecular dysfunctions in smooth muscle cells, myenteric neurons, and primary afferent neurons that may underlie IBS symptoms.

Lessons Learnt from Post-Infectious IBS

The development of IBS symptoms - altered bowel function and abdominal cramping in a subset of adult subjects exposed to severe enteric infections opened up an unprecedented opportunity to understand the etiology of this poorly understood disorder. Perhaps, for the reasons that these symptoms follow a severe enteric infection, and mucosal biopsy tissues are readily available, the focus of most studies thus far has been to show that mild/low-grade mucosal inflammation persisting after the initial infection has subsided causes the IBS symptoms. Parallel studies in non-infectious IBS patients, who did not have prior enteritis, showed similar mild mucosal inflammation. Together, these studies examined the mucosal infiltration of specific immune cells, increase of select inflammatory mediators, mast cell and enterochromaffin cell hyperplasia, and epithelial permeability. In spite of the fact that the data on these topics were not consistent among different studies and clinical trials with prednisone, fluoxetine, and ketotifen failed to provide relief of IBS symptoms, the predominant conclusions were that mild mucosal inflammation is the cause of IBS symptoms. However, the circular smooth muscle cells, and myenteric neurons are the primary regulators of gut motility function, while primary afferent neurons and CNS play essential roles in induction of visceral hypersensitivity - no explanation was provided as to how mild mucosal inflammation causes dysfunction in cells far removed. Accumulating evidence shows that mild mucosal inflammation in IBS patients is in physiological range. It has little deleterious effects on cells within its own environment and therefore it is unlikely to affect cells in the muscularis externa. This review discusses the disconnect between the focus on mild/low-grade mucosal inflammation and the potential mechanisms and molecular dysfunctions in smooth muscle cells, myenteric neurons, and primary afferent neurons that may underlie IBS symptoms.

Symptoms in patients with ulcerative colitis in remission are associated with visceral hypersensitivity and mast cell activity

OBJECTIVE

Patients with ulcerative colitis in remission (UCR) frequently report irritable bowel syndrome (IBS)-like symptoms. Recent studies have pointed to the role of mast cells in mediating visceral hypersensitivity in IBS. We hypothesized that visceral hypersensitivity is frequently present in patients with UCR and is related to the quantity and activity of mast cells in the sigmoid mucosa.

MATERIAL AND METHODS

A group of 17 controls and 19 patients with UCR were studied. Rectal compliance and perception were measured by electronic barostat. Sigmoid biopsies were taken to quantify the amount of mast cells, degranulating mast cells and mast cells in close proximity to mucosal nerve endings.

RESULTS

Visceroperception significantly increased in UCR (p < 0.05) versus controls. Rectal perception correlated positively with IBS-like symptoms in UCR (r = 0.969; p < 0.05). The amount of mucosal mast cells (per 100 crypts) was significantly increased in UCR versus controls: 228 ± 20 versus 163 ± 18 (p < 0.05). In the UCR patients a higher percentage of mucosal mast cells was in close proximity to nerve endings (58 ± 4 vs. 38 ± 3% in controls; p < 0.05) or was degranulating (40 ± 7 vs. 16 ± 4% in controls; p < 0.05). There was a significant but weak correlation between quantity of mucosal mast cells and pain perception (r = 0.32; p < 0.05).

CONCLUSION

Rectal hypersensitivity is associated with mucosal presence and activation of mast cells and with IBS-like symptoms in patients with UCR.

Idiopathic cystitis in domestic cats--beyond the lower urinary tract

Signs of lower urinary tract (LUT) disease in domestic cats can be acute or chronic, and can result from variable combinations of abnormalities within the lumen of the LUT, the parenchyma of the LUT itself, or other organ system(s) that then lead to LUT dysfunction. In the majority of cats with chronic signs of LUT dysfunction, no specific underlying cause can be confirmed after standard clinical evaluation of the LUT, so these cats typically are classified as having idiopathic cystitis. A syndrome in human beings commonly known as interstitial cystitis (IC) shares many features in common with these cats, permitting comparisons between the two species. A wide range of similarities in abnormalities has been identified between these syndromes outside as well as inside the LUT. A variety of potential familial and developmental risk factors also have been identified. These results have permitted generation of the hypothesis that some of these people have a disorder affecting the LUT rather than a disorder of the LUT. This perspective has suggested alternative diagnostic strategies and novel approaches to treatment, at least in cats. The purpose of this review is to summarize research investigations into the various abnormalities present in cats, to compare some of these findings with those identified in human beings, and to discuss how they might modify perceptions about the etiopathogenesis, diagnosis, and treatment of cats with this disease. Dedication: I dedicate this contribution to Professor Dennis J. Chew, whose collaboration, patience, and support made it all possible.

Descending inhibitory pain modulation is impaired in patients with chronic pancreatitis

BACKGROUND & AIMS

Pain is a prominent symptom in chronic pancreatitis (CP), but the underlying mechanisms are incompletely understood. We investigated the role of descending pain modulation from supraspinal structures as well as central nervous system sensitization in patients with pain from CP.

METHODS

Twenty-five patients with CP and 15 healthy volunteers were included. Descending pain modulation was investigated by diffuse noxious inhibitory control (a descending inhibitory response after conditioning stimulation). Central pain processing was investigated as the perceptual responses to multimodal (electrical, thermal, and mechanical) stimulations of the rectosigmoid and evoked brain potentials after electrical stimulation of the rectosigmoid.

RESULTS

Compared with healthy volunteers, the efficacy of diffuse noxious inhibitory control was reduced in patients with CP (13% +/- 21% vs 39% +/- 22%, respectively; F = 3.8; P = .01); central sensitization was indicated by remote hyperalgesia in the rectosigmoid to electrical stimulation (21 +/- 15 mA vs 27 +/- 15 mA; F = 6.2; P = .02) and heat stimulation (51 degrees C +/- 5 degrees C vs 53 degrees C +/- 4 degrees C; F = 5.9; P = .02). Compared with controls, patients with CP had increased latency of the early P1 peak to rectosigmoid stimulation (85 +/- 21 ms vs 108 +/- 28 ms, respectively; P = .02), possibly reflecting reorganization of central pain pathways.

CONCLUSIONS

Patients with CP have impairments in inhibitory pain modulation and evidence of central sensitization. Treatment of their pain therefore should focus not only on the pancreas, but also on descending pain modulation from supraspinal structures and central nervous system sensitization.

Anorectal function in patients with collagenous colitis in active and clinically quiescent phase, in comparison with healthy controls

BACKGROUND

Collagenous colitis (CC) is characterized by chronic watery diarrhea, a macroscopically normal colonic mucosa but typical microscopic inflammation. Chronic mucosal inflammation of the colon and rectum has earlier been associated with altered visceral sensitivity, but anorectal function has never been reported in cases of CC.

METHODS

Fifteen patients with CC in active phase recorded their symptoms. The severity of inflammation was determined in mucosal biopsies. Anorectal function was assessed and compared with that of 15 healthy volunteers of corresponding age and matched for gender. After 6 weeks of budesonide treatment when the patients were in clinical remission anorectal function was re-assessed.

KEY RESULTS

All patients had inflammation also in rectum. Patients in active phase had, during rectal balloon distension a higher rectal sensory threshold for the feeling of first sensation, compared with controls (P = 0.02). There were no differences in rectal sensory threshold for the feeling of urgency or maximum distension, between patients with CC in active phase and healthy controls. Rectal volume at first sensation was significantly greater in patients than in controls (P = 0.02), but there were no differences at urgency or maximum distension. Twelve of 15 patients completed 6 weeks of budesonide treatment and all went into clinical remission. No differences in anorectal function were measured when patients had active disease, compared with clinical remission.

CONCLUSIONS & INFERENCES

Collagenous colitis was not associated with rectal hypersensitivity or disturbed anal function despite rectal inflammation. On the contrary, the sensation threshold for light rectal pressure was elevated in patients with active CC.

Pathogenic mechanisms of postinfectious functional gastrointestinal disorders: results 3 years after gastroenteritis

OBJECTIVE

Functional gastrointestinal disorders (FGID) may appear after acute gastroenteritis. The aim of this study was to evaluate the possible mechanisms (inflammation, visceral hypersensitivity, psychological and immunogenetic factors) related to the development of postinfectious (PI) FGID 3 years after a Salmonella outbreak.

MATERIAL AND METHODS

Biopsies of the antrum, and right- and left colon from 16 PI-FGID patients, 8 PI control patients, and 18 healthy controls (H-controls) were processed for immunohistochemistry, cytokines, and mast-cell electron microscopy. DNA was typed for cytokine gene polymorphisms. Visceral sensitivity (satiety test and rectal barostat) and psychological factors (SCL-90 and vital events) were assessed.

RESULTS

The number of mast cells and T lymphocytes was similar among the groups in all locations. Mast cells within 5 microm of nerve fibers of both PI groups were increased compared to H-controls: (stomach: 5.6+/-1.2 versus 6.6+/-1.5 versus 2.5+/-1.1; right colon: 9.7+/-1.3 versus 8.0+/-1.3 versus 4.1+/-1.7; left colon: 8.9+/-0.9 versus 8.5+/-1.8 versus 2.2+/-2.0 per field) (p<0.05). No differences in the production of IL-1beta, IL-1ra, IL-6, and IL-10 or in their genotypes were found. PI-FGID patients showed a lower pain threshold to rectal distention (29+/-2 versus 37+/- 2 mmHg; p<0.05). Scores for anxiety (0.63+/-0.11 versus 0.28+/-0.14) and somatization (1.01+/-0.15 versus 0.45+/-0.15) were higher in PI-FGID patients than in PI controls (p<0.05). The number of stressful life events was not significantly different between both PI groups.

CONCLUSIONS

Three years after salmonellosis, PI-FGID patients showed no evidence of inflammation in the gastric or colonic mucosa, but visceral sensitivity and anxiety/somatization levels were increased. The close anatomical mast cell-nerve fibers relation does not seem to be related to the FGID but to the infection itself.

Sympathetic and parasympathetic regulation of rectal motility in rats

INTRODUCTION

The colon and rectum are regulated by the autonomic nervous system (ANS). Abnormalities of the ANS are associated with diseases of the colon and rectum while its modulation is a putative mechanism for sacral nerve stimulation. The purpose of this study is to establish a rat model elucidating the role of the efferent ANS on rectal motility.

MATERIALS AND METHODS

Rectal motility following transection or stimulation of parasympathetic pelvic nerves (PN) or sympathetic hypogastric nerves (HGN) was measured with rectal strain gauge transducers and quantified as a motility index (MI). Colonic transit was measured 24 hours after transection by calculating the geometric center (GC) of distribution of (51)Cr

RESULTS AND DISCUSSION

Transection of PN and HGN decreased MI to 518 +/- 185 g*s (p < 0.05) and increased MI to 5,029 +/- 1,954 g*s (p < 0.05), respectively, compared to sham (975 +/- 243 g*s). Sectioning of PN and HGN decreased transit with GC = 4.9 +/- 0.2 (p < 0.05) and increased transit with GC = 8.1 +/- 0.7 (p < 0.02), respectively, compared to sham (GC = 5.8 +/- 0.3). Stimulation of PN and HGN increased MI to 831 +/- 157% (p < 0.01) and decreased MI to 251 +/- 24% (p < 0.05), respectively.

CONCLUSION

Rectal motility is significantly altered by sectioning or stimulating either HGN or PN. This model may be useful in studying how sacral nerve stimulation exerts its effects and provide insight into the maladies of colonic motility.

Visceral afferents: what role in post-inflammatory pain?

Several weeks to several months after a bout of inflammation or an infectious event in a visceral organ, while inflammation or infection has resolved, defective nociceptive functions are sometimes still present, characterized by chronic pain symptoms, visceral hyperalgesia and allodynia. Visceral afferents which convey nociceptive messages have been shown to be hyperexcitable in inflammatory states. Only recently, studies have addressed visceral afferent electrical properties and neuroplastic changes in post-inflammatory situations. This review tries to appraise in post-inflammatory hypersensitive states, the most recent advances in the knowledge of visceral afferent inputs, together with in vivo recordings of visceral hyperalgesia and allodynia.

Fecal proteases from diarrheic-IBS and ulcerative colitis patients exert opposite effect on visceral sensitivity in mice

Elevated colonic luminal serine-protease (Ser-P) activity of diarrhea-predominant IBS (IBS-D) patients evokes a proteinase-activated receptor (PAR)-2-mediated colonic hypersensitivity in mice. Despite similarly elevated Ser-P levels in feces, patients with IBD exhibit visceral hypo- or normosensitivity to rectal distension, as opposed to IBS-D. To explain these discrepancies we studied the effect of colonic infusion of fecal supernatants from ulcerative colitis (UC) patients to colorectal mechanical sensitivity of mice and explored the involvement of PAR-4 and its activator Cathepsin-G (Cat-G). Fecal protease activities were assayed in healthy subjects, IBS-D and UC patients in presence or not of antiproteases or Cat-G inhibitor. Following intracolonic infusion of fecal supernatants from healthy subjects, IBS-D and UC patients or PAR-4 activating peptide (PAR-4-AP) or Cat-G, EMG response to colorectal balloon distension was recorded in mice. This nociceptive response was also determined after treatment with pepducin (PAR-4 antagonist) on UC supernatant or after a preincubation with antiproteases or Cat-G inhibitor. In contrast to IBS-D supernatant, UC supernatant promoted colonic hyposensitivity to distension, an effect mimicked by PAR-4-AP or Cat-G. UC supernatant-induced hypoalgesia was inhibited by a cocktail of antiproteases. However, blockade of PAR-4 or Cat-G inhibition resulted in colonic hypersensitivity similar to that observed after IBS-D supernatant infusion. Despite similarly elevated Ser-P activities, IBS-D and UC fecal supernatant display visceral pro- and antinociceptive effects in mice, respectively. Visceral hyposensitivity induced by fecal supernatant from UC patients results from PAR-4 activation by cathepsin-G, counterbalancing the pronociceptive effect of simultaneous PAR-2 activation.

Plasticity of enteric nerve functions in the inflamed and postinflamed gut

Inflammation of the gut alters the properties of the intrinsic and extrinsic neurons that innervate it. While the mechanisms of neuroplasticity differ amongst the inflammatory models that have been used, amongst various regions of the gut, and between intrinsic vs extrinsic neurons, a number of consistent features have been observed. For example, intrinsic and extrinsic primary afferent neurons become hyperexcitable in response to inflammation, and interneuronal synaptic transmission is facilitated in the enteric circuitry. These changes contribute to alterations in gut function and sensation in the inflamed bowel as well as functional disorders, and these changes persist for weeks beyond the point at which detectable inflammation has subsided. Thus, gaining a more thorough understanding of the mechanisms responsible for inflammation-induced neuroplasticity, and strategies to reverse these changes are clinically relevant goals. The purpose of this review is to summarize our current knowledge regarding neurophysiological changes that occur during and following intestinal inflammation, and to identify and address gaps in our knowledge regarding the role of enteric neuroplasticity in inflammatory and functional gastrointestinal disorders.

Pain and inflammatory bowel disease

Abdominal pain is a common symptom of inflammatory bowel disease (IBD: Crohn's disease, ulcerative colitis). Pain may arise from different mechanisms, which can include partial blockage and gut distention as well as severe intestinal inflammation. A majority of patients suffering from acute flares of IBD will experience pain, which will typically improve as disease activity decreases. However, a significant percentage of IBD patients continue experiencing symptoms of pain despite resolving inflammation and achieving what appears to be clinical remission. Current evidence suggests that sensory pathways sensitize during inflammation, leading to persistent changes in afferent neurons and central nervous system pain processing. Such persistent pain is not only a simple result of sensory input. Pain processing and even the activation of sensory pathways is modulated by arousal, emotion, and cognitive factors. Considering the high prevalence of iatrogenic as well as essential neuropsychiatric comorbidities including anxiety and depression in IBD patients, these central modulating factors may significantly contribute to the clinical manifestation of chronic pain. The improved understanding of peripheral and central pain mechanisms is leading to new treatment strategies that view pain as a biopsychosocial problem. Thus, improving the underlying inflammation, decreasing the excitability of sensitized afferent pathways, and altering emotional and/or cognitive functions may be required to more effectively address the difficult and disabling disease manifestations.

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.

G protein-coupled receptor kinase 6 controls post-inflammatory visceral hyperalgesia

Post-inflammatory pain is a poorly understood phenomenon. G protein-coupled receptors are involved in regulating pain signaling in the context of inflammation. G protein-coupled receptor kinases (GRK) modulate signaling through these receptors. We investigated whether GRK6 contributes to post-inflammatory visceral hyperalgesia. Colitis was induced in female mice by 1% dextran sodium sulphate in drinking water for 7 days. Disease score, colon length, and colonic cytokines were determined. On day 49, when animals had recovered from colitis, we induced visceral pain by intracolonic capsaicin instillation. Behavioral responses to capsaicin were monitored for 20 min. Referred hyperalgesia was measured using von Frey hairs. Spinal cord c-Fos was visualized by immunohistochemistry. In contrast to our earlier observations in male GRK6-/- and wild type (WT) mice, we did not detect differences in the course of colitis or in expression of colonic cytokines between female GRK6-/- and WT mice. After recovery from colitis, capsaicin-induced behavioral pain responses and spinal cord c-Fos expression were more pronounced in female GRK6-/- than WT mice. Naive GRK6-/- and WT animals did not differ in pain and c-Fos responses to capsaicin. Capsaicin-induced referred hyperalgesia post-colitis was increased in GRK6-/- compared to WT mice. However, referred hyperalgesia post-colitis was not affected by ablation of GRK6. Furthermore, in vitro IL-1beta sensitized the capsaicin receptor TRPV1 and this process was inhibited by over-expression of GRK6. We describe the novel concept that GRK6 inhibits post-inflammatory visceral hyperalgesia but does not contribute to visceral pain in naive animals. We propose that GRK6 regulates inflammation-induced sensitization of TRPV1.

Functional gastrointestinal disorders and visceral hypersensitivity in children and adolescents suffering from Crohn's disease

BACKGROUND

Symptoms of abdominal pain are reported by children with active Crohn's disease (CD). During remissions abdominal pain improves in most children but some of them continue to experience pain. We hypothesized that these patients may suffer from protracted abdominal pain related to functional gastrointestinal disorders (FGID) and visceral hypersensitivity. The objective was to characterize the symptoms and to measure the rectal sensory threshold for pain (RSTP) by barostat in CD children and adolescents suffering from abdominal pain despite remission.

METHODS

Eight patients (median age 14.5 years; range 9.8-17) with quiescent CD but suffering from chronic abdominal pain were studied by rectal barostat. At the same time they completed validated questionnaires to assess FGID, anxiety, and depression. They were compared to 10 control children and 8 children with FGID also investigated in our laboratory.

RESULTS

All patients fulfilled Rome II criteria for irritable bowel syndrome (n = 5), functional abdominal pain (n = 2), and functional dyspepsia (n = 1). RSTP was significantly lower in CD patients compared to the normal controls: median (range) 25 mmHg (15-29) versus 40 mmHg (30-48) (P < 0.01). RSTP was similar in patients and children with FGID. Rectal compliance was similar in patients, children with FGID, and controls. Seven of the 8 patients had scores indicating an anxiety problem.

CONCLUSIONS

Protracted abdominal pain that affects children and adolescents with quiescent CD is related to FGID associated with visceral hypersensitivity and anxiety. The incidence of FGID in children suffering from CD requires further investigation.

Review article: the psychoneuroimmunology of irritable bowel syndrome--an exploration of interactions between psychological, neurological and immunological observations

BACKGROUND

The pathogenesis of irritable bowel syndrome (IBS) is founded on interactive mechanisms. Disentangling these processes is a prerequisite for the development of effective drug therapy.

AIM

To identify the interaction between the various factors implicated in IBS.

METHODS

Articles pertaining to IBS pathogenesis focusing on psychoneuroimmunology were identified using following search terms: IBS, animal models, microbiota, probiotics, immunology, visceral hypersensitivity, imaging, psychology and visceral pain.

RESULTS

Cerebral imaging using MRI and proton emission tomography scanning has revealed differential regional cerebral activation, whereas stimuli induced activation has been captured by both MRI and cortical evoked potentials. At the peripheral neurological level, the concept of visceral hypersensitivity has been challenged as perhaps representing psychological traits with symptom over-reporting or hyper-vigilance. Gut mucosal immunology is thought to be relevant with immunological changes reflected as peripheral blood cytokine level changes. Molecular technology advances suggest a role for microbiota by activating the gut immunological system. These interactions have been examined in IBS animal models.

CONCLUSIONS

Translation of animal model findings to humans is needed to link the various psychological, neurological and immunological changes noted in IBS. This analysis may identify patient sub-groups, which will ultimately be critical for drug testing to be focused accordingly.

Novel techniques to study visceral hypersensitivity in irritable bowel syndrome

Visceral hypersensitivity has emerged as a key hypothesis in explaining the painful symptoms of irritable bowel syndrome (IBS), and it has been proposed as a "biologic marker" for the condition. Visceral hypersensitivity can be influenced by peripheral and central mechanisms affecting pain perception. The optimal method for its assessment in humans has not been determined. Current techniques include stimulation via the computerized barostat and electrical stimulation, response measures including the lower limb reflex, and brain imaging modalities such as functional MRI and positron emission tomography. It has been shown that IBS patients have decreased sensory thresholds to colonic and rectal balloon distention by barostat. Studies using electrical stimulation and the RIII lower limb reflex have further confirmed enhanced visceral perception in IBS. Evidence from more recent neuro-imaging studies suggests that IBS patients have abnormal activation of brain circuits involved in emotional and cognitive modulation of sensory information, resulting in ineffective pain modulation; these circuits may have a pathophysiologic role in enhancing visceral perception. There are few effective pharmacologic treatments that relieve IBS symptoms, and improved understanding of brain-gut interactions and factors relating to enhanced visceral perception may guide us in developing more efficacious treatments.

Postinflammatory visceral sensitivity and pain mechanisms

The inflammatory reaction is normally tightly regulated, and as soon as the original insult has been cleared, a resolution phase starts that aims at leading the tissues back to a normal physiological state. However, after intestinal inflammation, a number of patients develop postinflammatory hypersensitivity symptoms, which can be defined as an excessive sensitivity to gut nociceptive stimulation. The pain experienced by those patients has been largely studied in the context of postinfectious intestinal diseases. The mechanisms of postinflammatory persistent visceral pain involve peripheral and central neuroplastic changes, low-grade chronic inflammation that sensitizes visceral afferent pathways and sensitization of non-neuronal resident cells of the gut. Several molecular determinants such as neurokinins, serotonin, proteases and voltage-gated ion channels seem to play a significant role in the control of postinflammatory visceral sensation. This review tries to give insights into the mechanisms of persistent visceral pain following the resolution of intestinal inflammation and tries to identify what needs to be done to further advance the field of postinflammatory hypersensitivity clinical management.

Review article: gastrointestinal sensory and motor disturbances in inflammatory bowel disease - clinical relevance and pathophysiological mechanisms

BACKGROUND

It is well known that inflammation has a profound impact on the neuromuscular apparatus of the gastrointestinal tract during the inflammatory insult and in periods of remission, at the site of inflammation and at distance from this site. The importance of this interaction is illustrated by the higher prevalence of functional gut disorders in patients with inflammatory bowel disease.

AIMS

To document the epidemiological and clinical significance of functional alterations of gut motility and sensitivity in patients with inflammatory bowel disease and to formulate potential pathophysiological mechanisms.

RESULTS AND CONCLUSIONS

Functional gut disorders occur frequently in patients with inflammatory bowel disease, both during inflammatory episodes and in periods of remission, and have a major impact on their quality of life. The clinical manifestations of these motility and sensitivity disorders vary and are often difficult to treat, mainly because therapeutic guidelines and specific diagnostic tests to distinguish inflammatory bowel disease from functional gut disorders are lacking. Chronic bowel inflammation results in a complicated interaction between neuroendocrine serotonin-predominant cells of the mucosa, inflammatory cells (particularly mast cells) in the submucosa, the intrinsic and extrinsic innervation and the muscular apparatus including the interstitial cells of Cajal. The outcome of this interaction is a perturbation of gastrointestinal motor function, both locally and at distance from the site of inflammation and during both acute inflammation and remission.

Functional GI disorders: from animal models to drug development

Despite considerable efforts by academic researchers and by the pharmaceutical industry, the development of novel pharmacological treatments for irritable bowel syndrome (IBS) and other functional gastrointestinal (GI) disorders has been slow and disappointing. The traditional approach to identifying and evaluating novel drugs for these symptom-based syndromes has relied on a fairly standard algorithm using animal models, experimental medicine models and clinical trials. In the current article, the empirical basis for this process is reviewed, focusing on the utility of the assessment of visceral hypersensitivity and GI transit, in both animals and humans, as well as the predictive validity of preclinical and clinical models of IBS for identifying successful treatments for IBS symptoms and IBS-related quality of life impairment. A review of published evidence suggests that abdominal pain, defecation-related symptoms (urgency, straining) and psychological factors all contribute to overall symptom severity and to health-related quality of life. Correlations between readouts obtained in preclinical and clinical models and respective symptoms are small, and the ability to predict drug effectiveness for specific as well as for global IBS symptoms is limited. One possible drug development algorithm is proposed which focuses on pharmacological imaging approaches in both preclinical and clinical models, with decreased emphasis on evaluating compounds in symptom-related animal models, and more rapid screening of promising candidate compounds in man.

Symptom severity but not psychopathology predicts visceral hypersensitivity in irritable bowel syndrome

BACKGROUND & AIMS

Visceral hypersensitivity is a hallmark of irritable bowel syndrome (IBS), but the relationship with clinical symptoms and psychological factors has not been fully established. We aimed to (1) evaluate these variables in a large cohort of IBS patients, recruited from both hospital and general practice, and in healthy controls and (2) assess which of these factors predicts the occurrence of visceral hypersensitivity in IBS.

METHODS

Rectal compliance and perception (intensity, perception thresholds; visual analogue scale, 0-100 mm) were assessed by a rectal barostat study (ramp distention) in 101 IBS patients and 40 healthy volunteers. IBS symptom severity was scored by using a 14-day 5-item diary. Anxiety, depression, somatization, vigilance, pain coping, dysfunctional cognitions, psychoneuroticism, and quality of life were assessed with psychometric questionnaires.

RESULTS

Rectal compliance was significantly reduced in IBS patients compared with controls (P < .01), as were thresholds for pain (27 +/- 15 vs 35 +/- 8 mm Hg; P < .01) and urge (P < .05). Levels of anxiety, depression, neuroticism, somatization, and dysfunctional cognitions were significantly increased in IBS patients versus controls, whereas pain coping and quality of life were significantly worse. Hypersensitivity to rectal distention occurred in 33% of patients and was associated with increased symptom severity (P = .016), but not with demographic characteristics or psychological disturbances.

CONCLUSIONS

Hypersensitivity to balloon distention occurs in 33% of IBS patients and is predicted by symptom severity but not by psychological or demographic characteristics.

Visceral and somatic hypersensitivity in TNBS-induced colitis in rats

Inflammation of visceral structures in rats has been shown to produce visceral/somatic hyperalgesia. Our objectives were to determine if trinitrobenzene sulfonic acid (TNBS) induced colitis in rats leads to visceral/somatic hypersensitivity. Male Sprague-Dawley rats (200-250 g) were treated with 20 mg of TNBS in 50% ethanol (n = 40) or an equivalent volume of ethanol (n = 40) or saline (n = 25) via the colon. Colonic distension, Von Frey, Hargreaves, and tail reflex tests were used to evaluate for visceral, mechanical, and thermal sensitivity. The rats demonstrated visceral hypersensitivity at 2-28 days following TNBS administration (P < 0.0001). The ethanol-treated rats also demonstrated visceral hypersensitivity that resolved after day 14. TNBS-treated rats demonstrated somatic hypersensitivity at days 14-28 (P < 0.0001) in response to somatic stimuli of the hind paw. TNBS colitis is associated with visceral and somatic hypersensitivity in areas of somatotopic overlap. This model of colitis should allow further investigation into the mechanisms of visceral and somatic hypersensitivity.

NMDA Receptors and Colitis: Basic Science and Clinical Implications

During the last decade, research focusing primarily on alterations in the peripheral and central nervous system has improved our understanding of the pathophysiological mechanisms of chronic visceral pain. These studies have demonstrated significant physiological changes following injury to the viscera in the firing patterns of both primary afferent neurons that transmit nociceptive information from the viscera and in central neurons that process the nociceptive information. A number of receptors, neurotransmitters, cytokines, and second messenger systems in these neurons have been implicated in the enhancement of visceral nociception. N-methyl-d-aspartic acid (NMDA) receptors play an important role in chronic visceral pain and hypersensitivity that is present in the setting of colonic inflammation. NMDA receptors are found in the peripheral nervous system as well as the central terminal of primary afferent neurons and have been shown to play an important role in regulating the release of nociceptive neurotransmitters. Recent work has demonstrated the presence of NMDA receptors in the enteric nervous system. In this article, we will discuss more recent evidence of the role of NMDA receptors in visceral pain associated with colitis.

Acute colitis enhances responsiveness of lumbosacral spinal neurons to colorectal distension in rats

Aim of this study was to examine excitability and responsiveness of lumbosacral spinal neurons to colorectal distension (CRD) in rats with colitis induced by dextran sulphate sodium (DSS). Extracellular potentials of single L6-S2 spinal neurons were recorded in pentobarbital anesthetized and paralyzed rats. Results showed that 40/154 (26%) and 53/156 (34%) neurons responded to noxious CRD (80 mmHg, 20 s) in DSS-treated and control animals, respectively. Neurons with long-lasting and low-threshold excitatory responses to CRD were more frequently encountered in DSS-treated than in control groups (P < 0.05). The mean maximal excitatory responses of neurons to noxious CRD in DSS-treated animals were significantly greater and the duration of responses was longer than those in control animals (P < 0.05). It was suggested that lumbosacral spinal neurons with colorectal input had increased excitability and responsiveness following colitis, which might play an important role in development of colonic hypersensitivity and viscerosomatic referred pain.

Role of tachykinin NK(1) and NK(2) receptors in colonic sensitivity and stress-induced defecation in gerbils

The pharmacology of tachykinin NK receptors varies greatly among species. The aim of the present study was to assess the role of NK(1) and NK(2) receptors in mediating colorectal distension-evoked nociception and psychological stress-induced defecation in gerbils, a species with human-like NK receptor pharmacology. The effects of the selective NK(1) and NK(2) receptor antagonists, aprepitant and saredutant, on acute (1 h) restraint stress-evoked defecation and plasma adenocorticotropin (ACTH) levels in gerbils were assessed. The effects of antagonists alone or in combination on colorectal distension-evoked visceral pain in conscious gerbils were evaluated using the visceromotor response as a surrogate marker of pain. Restraint stress increased fecal pellet output 2-3-fold and plasma ACTH levels 9-fold. Aprepitant inhibited the defecatory and endocrine responses to stress by 50%, while saredutant completely normalized the same parameters. Visceral pain responses during colorectal distension were attenuated by both compounds, but aprepitant (19+/-6% inhibition, P<0.01) was slightly more effective than saredutant (10+/-9% inhibition, P<0.05). A combination of both compounds resulted in an additive effect (30+/-10% inhibition, P<0.01). The results demonstrate that NK(1) and NK(2) receptors are involved in stress-related colonic motor alterations and visceral pain responses in gerbils and that combined antagonism provides enhanced inhibition of visceral pain responses. This suggests that for therapeutic use in for instance functional gastrointestinal disorders, dual NK(1)/NK(2) receptor antagonists may provide better clinical outcome than selective compounds.

Involvement of metabotropic glutamate 5 receptor in visceral pain

Metabotropic glutamate 5 receptor (mGluR5) antagonists are effective in animal models of inflammatory and neuropathic pain. The involvement of mGluR5 in visceral pain pathways from the gastrointestinal tract is as yet unknown. We evaluated effects of mGluR5 antagonists on the colorectal distension (CRD)-evoked visceromotor (VMR) and cardiovascular responses in conscious rats, and on mechanosensory responses of mouse colorectal afferents in vitro. Sprague-Dawley rats were subjected to repeated, isobaric CRD (12 x 80 mmHg, for 30s with 5 min intervals). The VMR and cardiovascular responses to CRD were monitored. The mGluR5 antagonists MPEP (1-10 micromol/kg, i.v.) and MTEP (1-3 micromol/kg, i.v.) reduced the VMR to CRD dose-dependently with maximal inhibition of 52+/-8% (p<0.01) and 25+/-11% (p<0.05), respectively, without affecting colonic compliance. MPEP (10 micromol/kg, i.v.) reduced CRD-evoked increases in blood pressure and heart rate by 33+/-9% (p<0.01) and 35+/-8% (p<0.05), respectively. Single afferent recordings were made from mouse pelvic and splanchnic nerves of colorectal mechanoreceptors. Circumferential stretch (0-5 g force) elicited slowly-adapting excitation of action potentials in pelvic distension-sensitive afferents. This response was reduced 55-78% by 10 microM MTEP (p<0.05). Colonic probing (2g von Frey hair) activated serosal splanchnic afferents; their responses were reduced 50% by 10 microM MTEP (p<0.01). We conclude that mGluR5 antagonists inhibit CRD-evoked VMR and cardiovascular changes in conscious rats, through an effect, at least in part, at peripheral afferent endings. Thus, mGluR5 participates in mediating mechanically evoked visceral nociception in the gastrointestinal tract.

Increased visceral sensitivity to capsaicin after DSS-induced colitis in mice: spinal cord c-Fos expression and behavior

During acute and chronic inflammation visceral pain perception is altered. Conflicting data exist, however, on visceral pain perception in the postinflammatory phase. The aim of the present study was to investigate whether visceral pain perception is altered after resolution of dextran sodium sulfate (DSS)-induced inflammation of the colon. Visceral sensory function in mice was assessed by monitoring behavioral responses to intracolonic capsaicin instillation. Two hours later the number of c-Fos-positive neurons in lamina I/II and X of spinal cord segments T(12/13)-S1 was determined as a measure of neuronal activation. DSS colitis was induced by adding 1% of DSS to the drinking water. The course of DSS-induced colitis was assessed by determining the disease activity index score. Animals developed a transient colitis and had recovered at day 49. At this time point, cytokine levels and colon length were similar to control animals. Importantly, after resolution of DSS-induced colitis the behavioral response to intracolonic capsaicin was increased compared with control mice. Moreover, capsaicin-induced spinal cord neuronal c-Fos expression was significantly increased. Interestingly, after colitis animals also exhibited referred somatic hyperalgesia as measured with von Frey hairs on the abdominal wall. We conclude that postinflammatory visceral hyperalgesia occurs after resolution of DSS-induced colitis and that capsaicin-induced behavioral responses and spinal cord neuronal c-Fos activation are effective readouts for determination of visceral pain perception.

Increased colonic pain sensitivity in irritable bowel syndrome is the result of an increased tendency to report pain rather than increased neurosensory sensitivity

OBJECTIVE

The aim was to determine whether lower visceral pain thresholds in irritable bowel syndrome (IBS) primarily reflect physiological or psychological factors.

METHODS

Firstly, 121 IBS patients and 28 controls underwent balloon distensions in the descending colon using the ascending methods of limits (AML) to assess pain and urge thresholds. Secondly, sensory decision theory analysis was used to separate physiological from psychological components of perception: neurosensory sensitivity (p(A)) was measured by the ability to discriminate between 30 mm Hg vs 34 mm Hg distensions; psychological influences were measured by the report criterion-that is, the overall tendency to report pain, indexed by the median intensity rating for all distensions, independent of intensity. Psychological symptoms were assessed using the Brief Symptom Inventory (BSI).

RESULTS

IBS patients had lower AML pain thresholds (median: 28 mm Hg vs 40 mm Hg; p<0.001), but similar neurosensory sensitivity (median p(A): 0.5 vs 0.5; p = 0.69; 42.6% vs 42.9% were able to discriminate between the stimuli better than chance) and a greater tendency to report pain (median report criterion: 4.0 ("mild" pain) vs 5.2 ("weak" pain); p = 0.003). AML pain thresholds were not correlated with neurosensory sensitivity (r = -0.13; p = 0.14), but were strongly correlated with report criterion (r = 0.67; p<0.0001). Report criterion was inversely correlated with BSI somatisation (r = -0.26; p = 0.001) and BSI global score (r = -0.18; p = 0.035). Similar results were seen for the non-painful sensation of urgency.

CONCLUSION

Increased colonic sensitivity in IBS is strongly influenced by a psychological tendency to report pain and urge rather than increased neurosensory sensitivity.

Assessment of experimental pain from skin, muscle, and esophagus in patients with chronic pancreatitis

OBJECTIVES

Comprehensive experimental methods are of major relevance assessing pain mechanisms in patients with chronic pain. Chronic pancreatitis is thought to involve the sensory response in other visceral organs and somatic tissue. We, therefore, aimed at exploring the pain mechanisms in chronic pancreatitis (CP) using a multimodal and multitissue stimulation approach.

METHODS

Ten patients (mean age, 50 years) with CP and 13 healthy controls (mean age, 35 years) participated. None of the patients took analgesics regularly. All were exposed to multimodal (mechanical, thermal, and electrical) experimental pain in the skin, muscles, and esophagus.

RESULTS

The patients were hyposensitive to mechanical stimulations of the skin (P = 0.001), but there were no differences in the pain to thermal and electrical stimulations. In the muscle and esophagus, no differences in pain thresholds were found. The difference between single and repeated stimulations reflecting the degree of central sensitization was 17% in controls and 36% in patients (P = 0.001). The referred pain area to electrical stimulation was 30.1 cm2 in the patients and 7.7 cm2 for the controls (P = 0.02).

CONCLUSIONS

The findings suggest that the balance among central hyperexcitability, neuroplastic changes, and descending pain-modulating pathways may explain the pain response to experimental multimodal stimulations in CP. This will likely also reflect the clinical pain mechanisms and may have important impact in selection of treatment, where drugs with potential effects on these mechanisms should be used.

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.

Visceral pain perception is determined by the duration of colitis and associated neuropeptide expression in the mouse

BACKGROUND

Even though inflammation is a traditional tool for the induction of hyperalgesia in many tissues, recent observations suggest that not all inflammatory processes produce this change. Tolerance to colorectal distension (CRD) is reduced in patients with acute ulcerative colitis but is increased in patients with chronic inflammatory bowel disease. This suggests that the nature of the inflammatory infiltrate influences visceral perception.

AIM

To test this hypothesis by assessing responses to CRD in mice with mild, acute or chronic colitis.

METHODS

CRD responses were measured in mice with mild non-specific colitis, and dextran sodium sulphate (DSS)-induced acute and chronic colitis. Responses were compared with tissue infiltrate and damage, interleukin (IL)1beta and myeloperoxidase (MPO) activity and substance P, beta-endorphin and micro opioid receptor (MOR) expression.

RESULTS

Mild and acute colitis were associated with increased responsiveness to CRD. In contrast, CRD responses were not increased in mice with chronic colitis and this difference was not due to altered colonic wall compliance. MPO and IL1beta levels were greater in acute than in chronic colitis. Larger increases in tissue substance P were seen in acute than in chronic DSS, whereas CD4 T cells, beta-endorphin and MOR expression were evident only in chronic colitis. An inverse correlation was seen between substance P and MOR in these tissues.

CONCLUSIONS

Acute colitis increased responsiveness to CRD and is accompanied by an acute inflammatory infiltrate and increased tissue substance P. Chronic DSS is accompanied by an increase in beta-endorphin and MOR expression, and CD4 T cells, but no change in compliance or CRD responses. We conclude that acute inflammation generates hyperalgesia, whereas chronic inflammation involves infiltration by lymphocytes accompanied by MOR and beta-endorphin up regulation, and this provides an antinociceptive input that restores normal visceral perception.

Enteric descending and afferent neural signaling stimulated by giant migrating contractions: essential contributing factors to visceral pain

We investigated whether strong compression of an intestinal segment by giant migrating contractions (GMCs) initiates pseudoaffective signals from the gut, similar to those initiated by its distension with a balloon. The experiments were performed on conscious dogs by using close intra-arterial infusions of test substances that affect the receptors only in the infused segment. The stimulation of GMCs by close intra-arterial infusion of CGRP or distension of an intestinal segment by balloon increased the heart rate; the increase in heart rate was greater when the balloon distension and GMCs occurred concurrently in separate intestinal segments. The suppression of contractility in the distended segment blocked the increase in heart rate. By contrast, the stimulation of rhythmic phasic contractions (RPCs) or their spontaneous occurrence did not increase the heart rate. The occurrence of GMCs as well as intestinal distension also produced descending inhibition. The descending inhibition was blocked by the inhibition of nitric oxide synthase, but it was unaffected by the inhibition of adenylyl cyclase, purinergic receptors P2X and P2Y, and muscarinic receptors M(1) and M(2). The synaptic transmission for descending inhibition was mediated primarily by nicotinic receptors and activation of nitric oxide synthase. It was unaffected by the inhibition of tachykinin receptors NK(1), NK(2), and NK(3); serotonin receptors 5-HT(1A), 5-HT(2)/5-HT(1C), 5-HT(3), and 5-HT(4); and muscarinic receptors. Our findings show that GMCs, but not RPCs, initiate pseudoaffective signals from the gut. In the presence of visceral hypersensitivity or impaired descending inhibition, the GMCs may become a noxious stimulus.

Anxiety and pain symptoms in children with inflammatory bowel disease and functional gastrointestinal disorders undergoing colonoscopy

OBJECTIVE

To compare pain and anxiety scores between children with inflammatory bowel disease (IBD) and those with functional gastrointestinal disorders (FGID) undergoing colonoscopy and to examine the role of anxiety and procedure length in predicting reports of pain.

MATERIALS AND METHODS

Children ages 10 to 18 years undergoing colonoscopy (general anesthesia) for the first time completed pain and anxiety questionnaires immediately before the procedure and a pain questionnaire 48 hours after colonoscopy. The diagnosis was determined by chart review and physician interview.

RESULTS

Children with FGID had a longer duration of pain than those with IBD. Children with FGID endorsed a greater total number of the pain descriptors. The FGID group reported higher usual pain severity and greater postprocedural pain. No differences in anxiety were reported. However, higher levels of anxiety were associated with higher pain scores at the time of colonoscopy in children with IBD. It required significantly more time to perform colonoscopy in the IBD group than in the FGID group. Longer procedure duration was positively correlated with pain in children with FGID but not in children with IBD.

CONCLUSIONS

Children with FGID report more usual pain symptoms and may describe more pain after a colonoscopy when compared with children with IBD. Anxiety appears to play a role in pain severity after colonoscopy in children presenting with IBD, but not in children with FGID.

Mechanisms of hypersensitivity in IBS and functional disorders

General introduction The concept of visceral hypersensitivity is accepted as being germane to several functional gastrointestinal disorders (FGIDs). The causes or risk factors associated with this hypersensitivity are unclear. This article addresses the proposed mechanisms leading to hypersensitivity: from genetic to inflammatory disorders, from central to peripheral alterations of function. However, in order to place visceral hypersensitivity in a more global perspective as an aetiological factor for FGIDs, it also provides a review of recent evidence regarding the role of other peripheral mechanisms (the intraluminal milieu), as also genetic factors in the pathophysiology of these disorders. The article has been divided into five independent sections. The first three sections summarize the evidence of visceral hypersensitivity as a biological marker of functional gut disorders, the peripheral and central mechanisms involved, and the role of inflammation on hypersensitivity. In opposition to visceral hypersensitivity as an isolated phenomenon in functional gut disorders, the last two sections focus on the importance of peripheral mechanisms, like motor disturbances, specifically those resulting on altered transport of intestinal gas, and alterations of the intraluminal milieu and genetics.

Lymphocyte-mediated regulation of beta-endorphin in the myenteric plexus

Lymphocytes are antinociceptive and can modulate visceral pain perception in mice. Previously, we have shown that adoptive transfer of CD4+ T cells to severe combined immune-deficient (SCID) mice normalized immunodeficiency-related visceral hyperalgesia. Pain attenuation was associated with an increase in beta-endorphin release by T cells and an upregulation of beta-endorphin in the enteric nervous system. In this study, we investigated the relationship between T cells and opioid expression in the myenteric plexus. We examined opioid peptide and receptor expression in the myenteric plexus in the presence and absence of mucosal T cells. We found a positive association between T cells and beta-endorphin expression; this was accompanied by a downregulation of the micro-opioid receptor (MOR). In vitro, T helper (Th) type 1 and type 2 cytokine stimulation of CD4+ T cells or isolation of T cells from in vivo Th-polarized mice did not increase T cell release of beta-endorphin or the induction of beta-endorphin expression in the myenteric plexus. However, exogenous beta-endorphin did upregulate beta-endorphin expression, and both cycloheximide and naloxone methiodide inhibited peptide upregulation. Therefore, our results suggest that nonpolarized CD4+ T cells release beta-endorphin, which, through an interaction with MOR, stimulates an upregulation of beta-endorphin expression in the myenteric plexus. Thus, we propose that the mechanism underlying lymphocyte modulation of visceral pain involves T cell modulation of opioid expression in the enteric nervous system.

Somatic referral of visceral sensations and rectal sensory threshold for pain in children with functional gastrointestinal disorders

OBJECTIVE

To test the hypothesis that abdominal pain related to functional gastrointestinal disorders is associated with visceral hypersensitivity and abnormal perception of visceral sensations.

STUDY DESIGN

We examined 35 children (10-17.6 years old) fulfilling the Rome II criteria with irritable bowel syndrome (IBS; n = 21), functional abdominal pain (FAP; n = 8) or functional dyspepsia (FD; n = 6) compared with 10 control subjects (10.2-16.1 years). All underwent a rectal barostat examination. Painful sensations were reported on a human body diagram. The projections of sensations induced by rectal distension, the rectal sensory threshold for pain (RSTP) and the diagnostic value of RSTP measurements were measured.

RESULTS

Rectal distension induced sensations that projected to the S3 dermatome in the control subjects and FD and to aberrant sites in children with IBS and FAP. The RSTP was decreased in children with IBS and FAP compared with control subjects (P <.002) and was not different in children with FD compared with control subjects. At 30.8 mm Hg, the 5th percentile for the control subjects, the RSTP had a sensitivity rate of 89% and a specificity rate of 83% for IBS and FAP diagnosis.

CONCLUSION

Children with IBS and FAP are characterized by the association of rectal hypersensitivity and abnormal pain referral after rectal distension.

Increased responsiveness of rat colonic splanchnic afferents to 5-HT after inflammation and recovery

5-Hydroxytryptamine (5-HT) activates colonic splanchnic afferents, a mechanism by which it has been implicated in generating symptoms in postinfectious and postinflammatory states in humans. Here we compared mechanisms of colonic afferent activation by 5-HT and mechanical stimuli in normal and inflamed rat colon, and after recovery from inflammation. Colonic inflammation was induced in rats by dextran sulphate sodium. Single-fibre recordings of colonic lumbar splanchnic afferents revealed that 58% of endings responded to 5-HT (10(-4) m) in controls, 88% in acute inflammation (P<0.05) and 75% after 21 days recovery (P < 0.05 versus control). Maximal responses to 5-HT were also larger, and the estimated EC50 was reduced from 3.2 x 10(-6) to 8 x 10(-7) m in acute inflammation and recovered to 2 x 10(-6) m after recovery. Responsiveness to mechanical stimulation was unaffected. 5-HT3 receptor antagonism with alosetron reduced responses to 5-HT in controls but not during inflammation. Responses to the mast cell degranulator 48/80 mimicked those to 5-HT in inflamed tissue but not in controls, and more 5-HT-containing mast cells were seen close to calcitonin gene-related peptide-containing fibres in inflamed serosa. We conclude that colonic serosal and mesenteric endings exhibit increased sensitivity to 5-HT in inflammation, with both an increase in proportion of responders and an increase in sensitivity, which is maintained after healing of inflammation. This is associated with alterations in the roles of 5-HT3 receptors and mast cells.

Colorectal motor and sensitivity features in patients affected by ulcerative proctitis with constipation: a radiological and manometric controlled study

BACKGROUND AND AIM

Constipation may be present in ulcerative proctitis (UP), but its pathogenesis has not yet been evaluated. The aim of this article is to investigate functional and morphologic features of the anorectal region in patients with UP and constipation.

MATERIALS AND METHODS

Eleven patients with quiescent clinical, endoscopic, and histological UP and constipation and 10 patients with functional constipation (FC) underwent radiologic evaluation of intestinal transit time, anorectal manometry, and defecography. Transit time was measured with radiograms at 72 h after ingestion of radiopaque markers. Manometry was carried out using a continuous perfused catheter and a balloon inflated with increasing volumes of air. Defecography was performed after the injection of a barium-sulfate solution in the rectum, with the registration of videotapes during straining, squeezing, and evacuation.

RESULTS

Manometry showed in UP significantly lower values of rectal compliance than those in FC (3.10 and 5 mL/mmHg, respectively) (P = 0.03). Rectal sensitivity threshold was increased but without significant differences in UP and FC (30 and 50 mL air, respectively). At defecography, the median value of rectosacral space was increased in UP in comparison with FC (1.30 vs 0.8; P = 0.002). Lateral rectal diameter in UP was lower than in FC (6 and 8.8 cm, respectively; P = 0.016). Nonsymptomatic rectocele, mucosal prolapse, descending perineum, and abdominopelvic dyssynergy were equally present in UP and FC. The majority of UP patients showed a prolonged intestinal transit time similar to FC patients, and, more frequently, they showed low transit in the left colon in comparison with the right colon in comparison with FC patients.

CONCLUSIONS

This study suggests that constipation in UP may be correlated with rectal fibrosis, which reduces the transit of stools from the left colon. The concomitance of asymptomatic anorectal organic or functional alteration may contribute to worsen constipation.

Probiotic use in irritable bowel syndrome

Over the past several years, a number of studies have addressed the role of specific strains of bacteria, or combinations thereof, to alleviate certain symptoms of irritable bowel syndrome (IBS). More importantly, the precise factors that contribute to this therapeutic effect, such as modulations in cytokine levels and alterations in colonic motility, are being clarified. This review serves to summarize the evidence for the use of probiotics in the treatment of IBS and to place this information in clinical context. Potential future developments and areas of possible research are also discussed.

5-Amino-2-hydroxybenzoic acid 4-(5-thioxo-5H-[1,2]dithiol-3yl)-phenyl ester (ATB-429), a hydrogen sulfide-releasing derivative of mesalamine, exerts antinociceptive effects in a model of postinflammatory hypersensitivity

H(2)S functions as a neuromodulator and exerts anti-inflammatory activities. Recent data indicate that irritable bowel syndrome (IBS) is linked to inflammation of the gastrointestinal tract. In this study, we have investigated the role of a novel H(2)S-releasing derivative of mesalamine (5-amino-2-hydroxybenzoic acid 4-(5-thioxo-5H-[1,2]dithiol-3yl)-phenyl ester, ATB-429) in modulating nociception to colorectal distension (CRD), a model that mimics some features of IBS, in healthy and postcolitic rats. Four graded (0.4-1.6 ml of water) CRDs were produced in conscious rats, and colorectal sensitivity and pain were assessed by measuring the abdominal withdrawal response and spinal c-Fos expression. In healthy rats, ATB-429 dose dependently (25, 50, or 100 mg/kg) attenuated CRD-induced hypersensitivity and significantly inhibited CRD-induced overexpression of spinal c-FOS mRNA, whereas mesalamine had no effect. ATB-429-induced antinociception was reversed by glibenclamide, a ATP-sensitive K(+) (K(ATP)) channel inhibitor. The antinociceptive effect of ATB-429 was maintained in a rodent model of postinflammatory hypersensitivity (4 weeks after colitis induction). At a dose of 100 mg/kg, ATB-429 reversed the allodynic response caused by CRD in postcolitic rats. Colonic cyclooxygenase-2 and interkeukin-1beta mRNA and spinal c-FOS mRNA expression were significantly down-regulated by ATB-429, but not by mesalamine. ATB-429, but not mesalamine, increased blood concentrations of H(2)S in both healthy and postcolitic rats. Taken together, these data suggest that ATB-429 inhibits hypersensitivity induced by CRD in both healthy and postcolitic, allodynic rats by a K(ATP) channel-mediated mechanism. This study provides evidence that H(2)S-releasing drugs might have beneficial effects in the treatment of painful intestinal disorders.

Effects of serotonin transporter inhibition on gastrointestinal motility and colonic sensitivity in the mouse

Serotonin-selective reuptake transporter (SERT) expression is decreased in animal models of intestinal inflammation and in individuals with inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS), and it is possible that resultant changes in intestinal serotonin signalling contribute to the manifestation of clinical features associated with these disorders. The objective of this investigation was to determine whether inhibition of SERT function leads to changes in gut motility and sensitivity. Mice underwent a 14-day treatment with the SERT inhibitor, paroxetine (20 mg kg(-1)), or vehicle (saline/propylene glycol). Gastrointestinal (GI) transit following charcoal gavage, colonic motility, stool frequency and visceromotor responses to colorectal distension were evaluated. In mice treated with paroxetine, stool output was decreased, upper GI transit was delayed, and colonic sensitivity to a nociceptive stimulus was attenuated. These results demonstrate that reduced SERT function (via pharmacological blockade) significantly alters GI motility and sensitivity in mice, and support the concept that altered SERT expression and function could contribute to symptoms associated with IBS and IBD.

Assessment of visceral pain-related pseudo-affective responses to colorectal distension in mice by intracolonic manometric recordings

Recently, a new manometric method has been proposed to quantify visceromotor responses (VMR) to colorectal distension (CRD) in rats. This method is based on monitoring pressure changes within the distending balloon during CRD. This study assesses the applicability of such a technique to the quantification of VMRs to CRD in mice. Electrical activity of the abdominal muscles and pressure changes within the distending balloon (mechanical response) were simultaneously recorded in conscious mice during CRD (phasic ascending, 10-80 mm Hg, or repetitive, 55 mm Hg). There was a clear stimulus-response relationship with a strong correlation between electrical and mechanical responses during the ascending (r(2) = 0.899, n = 7) or repetitive phasic CRD (r(2) = 0.926, n = 8). Repetitive phasic distensions (55 mm Hg) increased the mechanical and electrical responses by 71 +/- 20% and 42 +/- 16%, respectively (pulses 10-12 vs. 1-3; n = 8, both P < .01). Atropine (0.5 or 1 mg/kg, subcutaneously) did not affect the mechanical response to CRD. The mu-opioid agonist, fentanyl (0.05 mg/kg, subcutaneously), completely prevented the sensitizing response associated to repetitive distensions. These results show that noninvasive, surgery-free manometry of intracolonic pressure is a reliable method to assess VMRs to CRD in mice. The analgesic effect of compounds could be determined, indicating that the method can be used in pharmacologic studies.

PERSPECTIVE

The model presented to assess visceral pain in mice allows a broad use of this species in pharmacological studies and will be of use in the characterization of potential targets and new drugs for the treatment of human pathologies with visceral pain arising from the gut as a significant component.

CD4+ T-cell modulation of visceral nociception in mice

BACKGROUND & AIMS

Although inflammatory and immune cells are present in the gut in the absence of pathology, their presence does not result in sensitization of sensory nerves, implying the existence of a local antinociceptive influence. We hypothesized that a component of the immune system exerts an antinociceptive influence, thus enabling the gut to function in the absence of undue pain or discomfort.

METHODS

Visceromotor responses to colorectal distention were measured in mice with severe combined immune deficiency (SCID) and their wild-type controls.

RESULTS

SCID mice exhibited significantly lower pain thresholds. Transfer of CD4(+) T, but not B lymphocytes, normalized visceral pain in these mice. The restoration of normal visceral nociception following T-cell reconstitution in SCID mice was blocked by naloxone methiodide. Using an enzyme immunoassay and immunohistochemistry for beta-endorphin, we showed that in vitro stimulation of T lymphocytes induced the synthesis and release of beta-endorphin and that transfer of T cells into SCID mice increased the expression of beta-endorphin in the enteric nervous system.

CONCLUSIONS

These findings indicate that the immune system is a critical determinant of visceral nociception and that T lymphocytes provide an important opioid-mediated antinociceptive influence in the gut.

The Manitoba Inflammatory Bowel Disease Cohort Study: prolonged symptoms before diagnosis--how much is irritable bowel syndrome?

BACKGROUND & AIMS

The Manitoba Inflammatory Bowel Disease (IBD) Cohort Study is a population-based prospective cohort study of recently diagnosed IBD (n=396). At enrollment, 162 (41%) indicated gastrointestinal symptom>or=3 years before diagnosis. We aimed to determine whether coexistence of irritable bowel syndrome (IBS) had a role in symptoms before IBD diagnosis.

METHODS

Patients were interviewed about symptoms and investigations before IBD diagnosis. Patients were assessed retrospectively for preexisting IBS.

RESULTS

Of 112 patients interviewed, 58% had Crohn's disease, 37% UC, 3% proctitis, and 2% indeterminant colitis. Symptoms at IBD diagnosis were considered the same (7%), worse (43%), different (20%), or both worse and different (30%) than at initial onset. Mean time between initial symptoms and diagnosis was 11 years (range, 3-48 years). Increasing age at IBD diagnosis correlated with a longer period after initial symptoms and diagnosis of IBD (r=.32, P<.0001). Gender and specific IBD diagnosis had no effect on this time period. Patients were identified as no previous IBS (51%), likely IBS (25%), and possible IBS (24%). Those with likely and possible IBS had a trend toward longer symptom duration before IBD diagnosis than those without IBS (P=.07). Of the total IBD cohort (n=396), considering only those with symptoms for >or=3 years before diagnosis, 14% were considered to have likely or possible IBS.

CONCLUSIONS

These data suggest that older patients and those with likely and possible preexisting IBS are more likely to experience longer symptom duration before diagnosis of IBD. The prevalence rate of IBS was similar to estimated base rates in the general population.

Pain and mechanical properties of the rectum in patients with active ulcerative colitis

BACKGROUND

The pain, urgency, and incontinence in ulcerative colitis may be related to changes in viscoelastic properties of the gut wall or to alterations of the sensory pathways. In the present study, we used an advanced rectal probe to study the mechanosensory and smooth muscle properties in patients with active disease.

METHODS

Nine patients with ulcerative colitis (mean age 39.5 years) with exacerbation limited to the rectum and sigmoid colon and 17 age-matched healthy subjects were included. The rectum was distended before and after pharmacological relaxation of the smooth muscle until moderate pain was reported, and the cross-sectional area, volume, pressure, tension, and strain were computed. To investigate central integration of a tonic stimulus, the bag was finally distended to the pain threshold; then, the cross-sectional area was held constant for 2 min.

RESULTS

The patients were hypersensitive to mechanical stimuli as assessed by the cross-sectional area (F = 21.7; P < 0.001). There were no differences in compliance or stiffness between the 2 groups, but the hypersensitivity was abolished after muscle relaxation. Together with the muscle analysis, this finding demonstrated that the smooth muscles were tonically contracted in the inflamed rectum, resulting in a decreased rectal circumference. The tonic distensions did not evoke central integration of the pain response, indicating that hyperalgesia is more likely related to peripheral factors.

CONCLUSIONS

Patients with active ulcerative colitis have hypersensitivity and increased tone of the smooth muscles, which may explain the symptoms. Drugs that affect smooth muscle contraction may be helpful in difficult cases.