Prolonged elevation of galanin and tachykinin expression in mucosal and myenteric enteric nerves in trinitrobenzene sulphonic acid colitis

Review: Occurrence and Distribution of Galanin in the Physiological and Inflammatory States in the Mammalian Gastrointestinal Tract

Galanin (GAL) is a broad-spectrum peptide that was first identified 37 years ago. GAL, which acts through three specific receptor subtypes, is one of the most important molecules on an ever-growing list of neurotransmitters. Recent studies indicate that this peptide is commonly present in the gastrointestinal (GI) tract and GAL distribution can be seen in the enteric nervous system (ENS). The function of the GAL in the gastrointestinal tract is, inter alia, to regulate motility and secretion. It should be noted that the distribution of neuropeptides is largely dependent on the research model, as well as the part of the gastrointestinal tract under study. During the development of digestive disorders, fluctuations in GAL levels were observed. The occurrence of GAL largely depends on the stage of the disease, e.g., in porcine experimental colitis GAL secretion is caused by infection with Brachyspira hyodysenteriae. Many authors have suggested that increased GAL presence is related to the involvement of GAL in organ renewal. Additionally, it is tempting to speculate that GAL may be used in the treatment of gastroenteritis. This review aims to present the function of GAL in the mammalian gastrointestinal tract under physiological conditions. In addition, since GAL is undoubtedly involved in the regulation of inflammatory processes, and the aim of this publication is to provide up-to-date knowledge of the distribution of GAL in experimental models of gastrointestinal inflammation, which may help to accurately determine the role of this peptide in inflammatory diseases and its potential future use in the treatment of gastrointestinal disorders.

The comprehensive pathophysiological changes in a novel rat model of postinflammatory visceral hypersensitivity

So far, a comprehensive animal model that can mimic both the central and peripheral pathophysiological changes of irritable bowel syndrome (IBS) is lacking. Here, we developed a novel IBS rat model combining trinitro-benzene-sulfonic acid (TNBS) and chronic unpredictable mild stress (CUMS) (designated as TC-IBS) and compared it with the TNBS-induced and CUMS-induced models. TC-IBS showed a pronounced depression phenotype with increased corticotropin-releasing hormone receptor (CRHR)1 and CRHR2 expression at the frontal cortex and increased serum ACTH concentration. Visceral hypersensitivity (VH), as evidenced by colorectal distention (CRD) test, was highest in TC-IBS, accompanied by increased serum 5-hydroxytryptamine (5-HT) level and colonic 5-HT receptor 3A (5-HT_3AR)/5-HT receptor 2B expression, impaired tight junction protein expression including occludin, zonula occludens-1, and phosphorylated myosin light chain. Palonosetron, a second generation of 5-HT_3AR antagonist, alleviated VH significantly in TC-IBS. 16S rRNA sequencing showed that TNBS plus CUMS induced a significant disturbance of the gut microbiota. Cytokine profile analysis of TC-IBS model indicated an innate immune activation both in serum and colonic mucosa. Further, fecal microbiota transplantation improved VH and some pathophysiological changes in TC-IBS. In summary, we established a postinflammatory IBS model covering multifactorial pathophysiological changes, which may help to develop therapies that target specific IBS subtype.-Ma, J., Li, J., Qian, M., He, N., Cao, Y., Liu, Y., Wu, K., He, S. The comprehensive pathophysiological changes in a novel rat model of postinflammatory visceral hypersensitivity.

Galaninergic intramural nerve and tissue reaction to antral ulcerations

BACKGROUND

Well-developed galaninergic gastric intramural nerve system is known to regulate multiple stomach functions in physiological and pathological conditions. Stomach ulcer, a disorder commonly occurring in humans and animals, is accompanied by inflammatory reaction. Inflammation can cause intramural neurons to change their neurochemical profile. Galanin and its receptors are involved in inflammation of many organs, however, their direct participation in stomach reaction to ulcer is not known. Therefore, the aim of the study was to investigate adaptive changes in the chemical coding of galaninergic intramural neurons and mRNA expression encoding Gal, GalR1, GalR2, GalR3 receptors in the region of the porcine stomach directly adjacent to the ulcer location.

METHODS

The experiment was performed on 24 pigs, divided into control and experimental groups. In 12 experimental animals, stomach antrum ulcers were experimentally induced by submucosal injection of acetic acid solution. Stomach wall directly adjacent to the ulcer was examined by: (1) double immunohistochemistry-to verify the changes in the number of galaninergic neurons (submucosal, myenteric) and fibers; (2) real-time PCR to verify changes in mRNA expression encoding galanin, GalR1, GalR2, GalR3 receptors.

KEY RESULTS

In the experimental animals, the number of Gal-immunoreactive submucosal perikarya was increased, while the number of galaninergic myenteric neurons and fibers (in all the stomach wall layers) remained unchanged. The expression of mRNA encoding all galanin receptors was increased.

CONCLUSIONS & INTERFERENCES

The results obtained unveiled the participation of galanin and galanin receptors in the stomach tissue response to antral ulcerations.

The Pathophysiology of Colonic Diverticulosis: Inflammation versus Constipation?

Background

Diverticulosis of the colon is the most common anatomic alteration of the human colon, but the pathophysiologic mechanisms of its occurrence are not completely understood.

Summary

Constipation has been considered the key factor for diverticulosis occurrence. However, several fine papers questioned this pathogenetic hypothesis, showing on the contrary an inverse relationship between low number of bowel movements and diverticulosis occurrence. In the last years, several papers have showed the role of low-grade inflammation in the occurrence of symptoms in people having diverticulosis, as well as its role on symptom persistence following acute diverticulitis, even if the evidence available is not so strong. Although the trigger of this low-grade inflammation is currently under debate, some preliminary evidence found colonic dysbiosis linked to symptom occurrence in those patients.

Key Messages

Constipation no longer seems the leading cause for diverticulosis occurrence, while low-grade inflammation could play a role in symptom occurrence.

Post-Infectious Irritable Bowel Syndrome

PURPOSE OF REVIEW

Post-infectious irritable bowel syndrome (PI-IBS) is characterized by persistent abdominal pain and diarrhea, typically following an episode of infectious gastroenteritis. The mechanisms that underlie IBS-D remain elusive, but PI-IBS provides a mechanistic model of this disorder. This review provides an up-to-date appraisal of the pathophysiology, clinical features, and management approaches for PI-IBS.

RECENT FINDINGS

Disordered immune reactions and release of cytokines with resultant gut inflammation and dysfunction appear to be key features of PI-IBS. Disordered brain-gut-microbiota interactions, type of infecting agent, and host-genetic susceptibility are risk factors but also are reasons for the varying spectrum of clinical severity. Although prognosis is generally good, symptoms and inflammation may persist for a long time. Symptomatic relief with antidiarrheals, antispasmodics, 5HT₃ antagonists, mesalamine, probiotics, and low-dose antidepressants remain the primary approaches, but in some difficult cases, a combination of drugs that target the pathophysiology may be helpful. PI-IBS has many overlapping features with IBS-D and shares similar pathophysiology and management approaches.

IBS and IBD - separate entities or on a spectrum?

The acute phase of IBD with inflamed gut and often ulcerated mucosa is clearly different from the apparently normal mucosa characteristic of IBS. However, more detailed assessment has detected immune activation, increased gut permeability, increased mucosal serotonin availability, abnormalities of enteric nerve structure and function, and dysbiosis in gut microbiota in IBS - all features seen in IBD. Furthermore, as treatments for inflammation in IBD have become more effective it is now apparent that ∼1 in 3 patients with IBD in remission from inflammation still have persistent abnormalities of sensation, motility and gut microbiota, which might cause IBS-like symptoms. This Perspective explores the overlap between IBS and IBD and their treatments, proposing future directions for research in this stimulating area.

The Influence of Gastric Antral Ulcerations on the Expression of Galanin and GalR1, GalR2, GalR3 Receptors in the Pylorus with Regard to Gastric Intrinsic Innervation of the Pyloric Sphincter

Gastric antrum ulcerations are common disorders occurring in humans and animals. Such localization of ulcers disturbs the gastric emptying process, which is precisely controlled by the pylorus. Galanin (Gal) and its receptors are commonly accepted to participate in the regulation of inflammatory processes and neuronal plasticity. Their role in the regulation of gastrointestinal motility is also widely described. However, there is lack of data considering antral ulcerations in relation to changes in the expression of Gal and GalR1, GalR2, GalR3 receptors in the pyloric wall tissue and galaninergic intramural innervation of the pylorus. Two groups of pigs were used in the study: healthy gilts and gilts with experimentally induced antral ulcers. By double immunocytochemistry percentages of myenteric and submucosal neurons expressing Gal-immunoreactivity were determined in the pyloric wall tissue and in the population of gastric descending neurons supplying the pyloric sphincter (labelled by retrograde Fast Blue neuronal tracer). The percentage of Gal-immunoreactive neurons increased only in the myenteric plexus of the pyloric wall (from 16.14±2.06% in control to 25.5±2.07% in experimental animals), while no significant differences in other neuronal populations were observed between animals of both groups. Real-Time PCR revealed the increased expression of mRNA encoding Gal and GalR1 receptor in the pyloric wall tissue of the experimental animals, while the expression(s) of GalR2 and GalR3 were not significantly changed. The results obtained suggest the involvement of Gal, GalR1 and galaninergic pyloric myenteric neurons in the response of pyloric wall structures to antral ulcerations.

Diverticulosis today: unfashionable and still under-researched

Diverticulosis of the colon is a widespread disease, and its prevalence is increasing especially in the developing world. The underlying pathological mechanisms that cause the formation of colonic diverticula remain unclear but are likely to be the result of complex interactions among age, diet, genetic factors, colonic motility, and changes in colonic structure. The large majority of patients remain asymptomatic throughout their life, one fifth of them become symptomatic (developing the so-called 'diverticular disease') while only a minority of these will develop acute diverticulitis. The factors predicting the development of symptoms remain to be identified. Again, it is generally recognized that diverticular disease occurrence is probably related to complex interactions among colonic motility, diet, lifestyle, and genetic features. Changes in intestinal microflora due to low-fiber diet and consequent low-grade inflammation are thought to be one of the mechanisms responsible for symptoms occurrence of both diverticular disease and acute diverticulitis. Current therapeutic approaches with rifaximin and mesalazine to treat the symptoms seem to be promising. Antibiotic treatment is currently advised only in acute complicated diverticulitis, and no treatment has currently proven effective in preventing the recurrence of acute diverticulitis. Further studies are required in order to clarify the reasons why diverticulosis occurs and the factors triggering occurrence of symptoms. Moreover, the reasons why rifaximin and mesalazine work in symptomatic diverticular disease but not in acute diverticulitis are yet to be elucidated.

Review article: the pathophysiology and medical management of diverticulosis and diverticular disease of the colon

BACKGROUND

The incidence of diverticulosis and diverticular disease of the colon, including diverticulitis, is increasing worldwide, and becoming a significant burden on national health systems. Treatment of patients with diverticulosis and DD is generally based on high-fibre diet and antibiotics, respectively. However, new pathophysiological knowledge suggests that further treatment may be useful.

AIM

To review the current treatment of diverticulosis and diverticular disease.

METHODS

A search of PubMed and Medline databases was performed to identify articles relevant to the management of diverticulosis and diverticular disease. Major international conferences were also reviewed.

RESULTS

Two randomised controlled trials (RCT) found the role of antibiotics in managing acute diverticulitis to be questionable, particularly in patients with no complicating comorbidities. One RCT found mesalazine to be effective in preventing acute diverticulitis in patients with symptomatic uncomplicated diverticular disease. The role of rifaximin or mesalazine in preventing diverticulitis recurrence, based on the results of 1 and 4 RCTs, respectively, remains unclear. RCTs found rifaximin and mesalazine to be effective in treating symptomatic uncomplicated diverticular disease. The use of probiotics in diverticular disease and in preventing acute diverticulitis occurrence/recurrence appears promising but unconclusive. Finally, the role of fibre in treating diverticulosis remains unclear.

CONCLUSIONS

Available evidence suggests that antibiotics have a role only in the treatment of complicated diverticulitis. It appears to be some evidence for a role for rifaximin and mesalazine in treating symptomatic uncomplicated diverticular disease. Finally, there is not currently adequate evidence to recommend any medical treatment for the prevention of diverticulitis recurrence.

Inflammation-induced abnormalities in the subcellular localization and trafficking of the neurokinin 1 receptor in the enteric nervous system

Activated G protein-coupled receptors traffic to endosomes and are sorted to recycling or degradative pathways. Endosomes are also a site of receptor signaling of sustained and pathophysiologically important processes, including inflammation. However, the mechanisms of endosomal sorting of receptors and the impact of disease on trafficking have not been fully defined. We examined the effects of inflammation on the subcellular distribution and trafficking of the substance P (SP) neurokinin 1 receptor (NK1R) in enteric neurons. We studied NK1R trafficking in enteric neurons of the mouse colon using immunofluorescence and confocal microscopy. The impact of inflammation was studied in IL10(-/-)-piroxicam and trinitrobenzenesulfonic acid colitis models. NK1R was localized to the plasma membrane of myenteric and submucosal neurons of the uninflamed colon. SP evoked NK1R endocytosis and recycling. Deletion of β-arrestin2, which associates with the activated NK1R, accelerated recycling. Inhibition of endothelin-converting enzyme-1 (ECE-1), which degrades endosomal SP, prevented recycling. Inflammation was associated with NK1R endocytosis in myenteric but not submucosal neurons. Whereas the NK1R in uninflamed neurons recycled within 60 min, NK1R recycling in inflamed neurons was delayed for >120 min, suggesting defective recycling machinery. Inflammation was associated with β-arrestin2 upregulation and ECE-1 downregulation, which may contribute to the defective NK1R recycling. We conclude that inflammation evokes redistribution of NK1R from the plasma membrane to endosomes of myenteric neurons through enhanced SP release and defective NK1R recycling. Defective recycling may be secondary to upregulation of β-arrestin2 and downregulation of ECE-1. Internalized NK1R may generate sustained proinflammatory signals that disrupt normal neuronal functions.

Changing views on diverticular disease: impact of aging, obesity, diet, and microbiota

The development of colonic diverticulosis is a common aging change in industrialized nations. While most patients have asymptomatic diverticulosis, around one in five develops symptomatic diverticular disease. This is characterized by recurrent abdominal pain and disturbed bowel habit. Some of the pain episodes are prolonged and are due to acute diverticulitis, which itself may be complicated by abscess, perforation, fistulation, or stricture formation. Risk factors favouring the development of symptomatic diverticular disease include obesity, smoking and diets low in fiber but high in red meat and animal fat. What determines the transition from asymptomatic diverticulosis to symptomatic diverticular disease is unclear but neuromuscular changes following acute diverticulitis may be responsible in some cases. The severity of symptoms generated depends on cerebral pain processing which is influenced by psychosocial factors. These are important considerations in deciding optimal patient management. Prior theories of the cause of diverticulosis suggested that constipation was an important cause, but new data challenge this and has provoked new ideas. Underlying mechanisms causing diverticulosis include weakening of the colonic wall and/or degenerative changes in the enteric nerves. Dietary induced changes in microbiota and the host inflammatory response may underlie the subsequent development of acute/chronic diverticulitis and its sequela.

Editorial: new thoughts on the association between diverticulosis and irritable bowel syndrome

As our population ages it is increasingly common to encounter patients with irritable bowel syndrome (IBS)-like symptoms and diverticulosis, but the nature of the association is obscure. This Editorial discusses the paper from Japan showing an association between IBS-like symptoms and left-sided but not right-sided diverticulosis. The left colon with its higher motor activity is more likely to be associated with complications of diverticulosis, including perforation and abscess formation. The underlying pathophysiology of the syndrome of post-diverticulitis IBS is discussed and clinical markers of centrally driven symptoms suggested as a means to avoid ineffective colonic resections in those with IBS-like diverticular disease.

Review article: The pathogenesis and management of acute colonic diverticulitis

BACKGROUND

Acute diverticulitis, defined as acute inflammation associated with a colonic diverticulum, is a common emergency presentation managed by both surgeons and physicians. There have been advances in both the medical and the surgical treatments offered to patients in recent years.

AIM

To review the current understanding of the aetiology and treatment of acute diverticulitis.

METHODS

A search of PubMed and Medline databases was performed to identify articles relevant to the aetiology, pathogenesis and management of acute diverticulitis.

RESULTS

There are 75 hospital admissions per year for acute diverticulitis per 100,000 of the population in the United States. Recent reports suggest a 26% increase in admissions over a 7-year period. Factors predisposing to the development of acute diverticulitis include obesity, smoking, diet, lack of physical activity and medication use such as aspirin and nonsteroidal anti-inflammatory drugs. The condition is associated with a low mortality of about 1% following medical therapy, rising to 4% in-hospital mortality in those requiring surgery. There is limited evidence on the efficacy of individual antibiotic regimens, and antibiotic treatment may not be required in all patients. The rates of recurrence reported for patients with acute diverticulitis following medical management vary from 13% to 36%. The surgical management of those patients who fail medical treatment has moved towards a laparoscopic nonresectional approach; however, the evidence supporting this is limited.

CONCLUSIONS

Further high-quality randomised controlled trials are required of both medical and surgical treatments in patients with acute diverticulitis, if management is to be evidence-based.

An Update on Post-infectious Irritable Bowel Syndrome: Role of Genetics, Immune Activation, Serotonin and Altered Microbiome

The literature on post-infectious irritable bowel syndrome (IBS) is reviewed with special emphasis on recent new data. Further accounts of this phenomenon continue to be reported following a range of infections including giardiasis as well as viral and bacterial gastroenteritis. Risk factors such as severity of initial illness, female gender together with adverse psychological factors have been confirmed. Recent evidence of a genetic predisposition needs replication. Animal studies suggest activation of mast cells and inflammation driven impairment of serotonin transporter may be important, which are findings supported by some recent human studies in IBS with diarrhoea. Experimentally induced inflammation leads to damage and remodelling of enteric nerves. Similar changes have been reported in IBS patients with increase in nerves expressing transient receptor potential cation channel V1. While changes in microbiota are very likely this area has yet to be explored using modern techniques. Since the prognosis is for slow improvement, treatments should currently target the key symptoms of diarrhoea and abdominal pain. Future therapies aimed at correcting underlying mechanisms including immune activation and serotonin excess are currently being explored and may provide better treatments in the future.

Perception and the origin of symptoms in diverticular disease

Colonic diverticulosis is a common condition and although the majority of patients are asymptomatic up to 20% experience altered bowel habit and abdominal pain. The mechanisms underlying these symptoms are unclear but several theories now exist. This article briefly outlines a model of GI perception and then highlights past and current theories that may explain the development of symptoms in patients with diverticulosis.

Is it diverticular disease or is it irritable bowel syndrome?

Symptomatic diverticular disease (SYMP-DD) and irritable bowel syndrome (IBS) share many features. Both are characterised by recurrent episodes of abdominal pain which may be slightly more frequent in IBS than SYMP-DD. They may also both exhibit an erratic bowel habit with diarrhoea, constipation and alternating types. It is important to assess anxiety, depression and somatisation since this can be increased in both types of patients and may be associated with visceral hypersensitivity. There are also significant differences between IBS and SYMP-DD. In particular, SYMP-DD patients are older, lack the female predominance seen in IBS and may often have fever with prolonged episodes of pain. For them, abnormalities of the gut are probably more important than cerebral factors, while for IBS the reverse is true. Treatments should be directed at the predominant abnormality which will vary in every patient.

The effects of galanin on dorsal root ganglion neurons with high glucose treatment in vitro

The exposure of neurons to high glucose concentrations is considered a determinant of diabetic neuropathy. The extracellular high concentration of glucose can cause neuronal cellular damage. Galanin (Gal) not only plays a role in processing of sensory information but also participates in energy homeostasis and glucoregulation. However, the effects of Gal on dorsal root ganglion (DRG) neurons with high glucose are not clear. Using an in vitro model of high glucose-treated DRG neurons in culture, the effects of Gal on intracellular reactive oxygen species (ROS) expression, cell viability, apoptosis, expression of Gal and its receptors (GalR1 and GalR2) of DRG neurons were investigated. Neurons were dissociated from embryonic day 15 (E15) rat DRG and cultured for 48 h and then maintained in serum-free neurobasal medium containing high glucose (45 mmol/L) or normal glucose (25 mmol/L) for 24h. Mannitol (20 mmol/L) was also used to create a high osmotic pressure mimicking the high glucose condition. The results showed that high glucose caused a rapid increasing of intracellular ROS, decreases of cell viability, and upregulation of Gal and its mRNA. Exogenous Gal (1 μmol/L) inhibited the above effects caused by high glucose. Interestingly, high glucose caused downregulation of GalR1 and its mRNA and administration of exogenous Gal could further decrease their expression, whereas expression of GalR2 and its mRNA was not affected at different experimental conditions. The results of the present study indicate for the first time that Gal and its receptor system are involved in high glucose-induced DRG neuronal injury. The contribution of exogenous Gal on neuroprotection appears to be quite significant. These results provide rationale and experimental evidence for development and further studies of Gal on therapeutic strategy for improving diabetic neuropathy.

Dysfunction of neurogenic VIP-mediated relaxation in mouse distal colon with dextran sulfate sodium-induced colitis

Vasoactive intestinal peptide (VIP) regulates various functions including motility and immune homeostasis in colon. The VIP system including its receptors has been established to control the development of ulcerative colitis, but the functional changes of the system-regulated motility in colon with ulcerative colitis are not well understood. In this study, we investigated VIP-related contractile responses in distal colon from mice with dextran sulfate sodium (DSS)-induced acute colitis. Electrical stimulation (ES) under our conditions caused relaxation during ES and contraction after withdrawal of ES in a tetrodotoxin-sensitive manner. Pharmacological analyses showed two phases of ES-induced relaxation: a transient neuronal nitric oxide (NO) synthase-dependent phase (I), and a continued VIP receptor-mediated phase (II). Inhibition of VIP receptors and protein kinase A decreased both phases. In colon from DSS-treated mice, ES-induced phase II (also phase I) and VIP-induced, but not cyclic AMP analog-induced, relaxation were decreased. Stimulation with VIP significantly increased cyclic AMP formation in colon preparations from control but not DSS-treated mice. In colon from DSS-treated mice, the basal cyclic AMP level was markedly greater without changes in the level of VIP receptor VPAC(2). Isoprenaline- and forskolin-induced relaxation and cyclic AMP formation were not changed by DSS treatment. These findings suggest that dysfunction of VIP receptors in muscles, in addition to loss of the neuronal VIP and NO pathways, are involved in abnormal motility in mouse colon with DSS-induced colitis.

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.

Enteric nervous system in the small intestine: pathophysiology and clinical implications. Curr Gastroenterol Rep. 2010;12:358-365. [PMID: 20725870 DOI: 10.1007/s11894-010-0129-9]

The digestive system is endowed with its own, local nervous system, referred to as the enteric nervous system (ENS). Given the varied functions of small intestine, its ENS has developed individualized characteristics relating to motility, secretion, digestion, and inflammation. The ENS regulates the major enteric processes such as immune response, detecting nutrients, motility, microvascular circulation, intestinal barrier function, and epithelial secretion of fluids, ions, and bioactive peptides. Remarkable progress has been made in understanding the signaling pathways in this complex system and how they work. In this article, we focus on recent advances that have led to new insights into small intestinal ENS function and the development of new therapies.

Infection, inflammation, and the irritable bowel syndrome

Gastrointestinal infection is ubiquitous worldwide though the pattern of infection varies widely. Poor hygiene and lack of piped water is associated with a high incidence of childhood infection, both viral and bacterial. However in developed countries bacterial infection is commoner in young adults. Studies of bacterial infections in developed countries suggest 75% of adults fully recover, however around 25% have long lasting changes in bowel habit and a smaller number develop the irritable bowel syndrome (IBS). Whether the incidence is similar in developing countries is unknown. Post-infective IBS (PI-IBS) shares many features with unselected IBS but by having a defined onset allows better definition of risk factors. These are in order of importance: severity of initial illness, smoking, female gender and adverse psychological factors. Symptoms may last many years for reasons which are unclear. They are likely to include genetic factors controlling the immune response, alterations in serotonin signaling, low grade mucosal inflammation maintained by psychological stressors and alterations in gut microbiota. As yet there are no proven specific treatments, though 5HT(3) receptor antagonists, anti-inflammatory agents and probiotics are all logical treatments which should be examined in large well-designed randomised placebo controlled trials.

Post inflammatory damage to the enteric nervous system in diverticular disease and its relationship to symptoms

Some patients with colonic diverticula suffer recurrent abdominal pain and exhibit visceral hypersensitivity, though the mechanism is unclear. Prior diverticulitis increases the risk of being symptomatic while experimental colitis in animals increases expression of neuropeptides within the enteric nervous system (ENS) which may mediate visceral hypersensitivity. Our aim was to determine the expression of neuropeptides within the ENS in diverticulitis (study 1) and in patients with symptomatic disease (study 2). Study 1 - Nerves in colonic resection specimens with either acute diverticulitis (AD, n = 16) or chronic diverticulitis (CD, n = 16) were assessed for neuropeptide expression recording % area staining with protein gene product (PGP9.5), substance P (SP), neuropeptide K (NPK), pituitary adenylate cyclase activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP) and galanin. Study 2 - Seventeen symptomatic and 15 asymptomatic patients with colonic diverticula underwent flexible sigmoidoscopy and multiple peridiverticular mucosal biopsies. Study 1- Neural tissue, as assessed by PGP staining was increased to a similar degree in circular muscle in both AD and CD. The CD specimens showed significant increases in the immunoreactivity of SP, NPK and galanin in both mucosal and circular muscle layer compared with controls. Study 2 - Mucosal histology was normal and PGP9.5 staining was similar between groups however patients with symptomatic diverticular disease demonstrated significantly higher levels of SP, NPK, VIP, PACAP and galanin within the mucosal plexus. Patients with symptomatic diverticular disease exhibit increased neuropeptides in mucosal biopsies which may reflect resolved prior inflammation, as it parallels the changes seen in acute and chronic diverticulitis.

Post-inflammatory modification of colonic afferent mechanosensitivity

1. The present review discusses interactions between the immune and nervous systems in post-infectious irritable bowel syndrome (PI-IBS). 2. Visceral pain is the single symptom that most affects the quality of life of patients with irritable bowel syndrome (IBS), yet it is the least successfully managed. An underlying hypersensitivity of colonic afferents to mechanical stimuli has long been implicated in visceral pain in IBS, but little more is known of the physiological aetiology. 3. The PI-IBS patients are a cohort of IBS patients who attribute their symptoms to a preceding gastrointestinal infection by pathogens such as Campylobacter or Salmonella. Current evidence suggests that the immune system remains activated in these patients and contributes to their visceral hypersensitivity. This is characterized by a shift in the phenotype of circulating immune cells towards a Type 1 (Th1 predominating) state. Products from these immune cells sensitize colonic afferents to mechanical stimuli. 4. Rectal instillation of trinitrobenzene sulphonic acid induces a Th1-mediated inflammatory response, consistent with clinical observations in PI-IBS. The visceral hypersensitivity observed in this model is biphasic, with an initial onset characterized by visceral hypersensitivity correlating with histological damage followed by a delayed phase that occurs after histological recovery. Interestingly, this chronic visceral hypersensitivity is mediated by afferents in closest apposition to blood vessels, but furthest from the initial site of damage. 5. Both clinical and experimental evidence indicates that chronic dysregulation of the immune system induces visceral afferent hypersensitivity and, therefore, may be the central mechanism underlying PI-IBS.

Postinfectious irritable bowel syndrome

Approximately 1 in ten patients with irritable bowel syndrome (IBS) believe their IBS began with an infectious illness. Prospective studies have shown that 3% to 36% of enteric infections lead to persistent new IBS symptoms; the precise incidence depends on the infecting organism. Whereas viral gastroenteritis seems to have only short-term effects, bacterial enteritis and protozoan and helminth infections are followed by prolonged postinfective IBS (PI-IBS). Risk factors for developing PI-IBS include, in order of importance, prolonged duration of initial illness, toxicity of infecting bacterial strain, smoking, mucosal markers of inflammation, female gender, depression, hypochondriasis, and adverse life events in the preceding 3 months. Age older than 60 years might protect against PI-IBS, whereas treatment with antibiotics has been associated with increased risk. The mechanisms that cause PI-IBS are unknown but could include residual inflammation or persistent changes in mucosal immunocytes, enterochromaffin and mast cells, enteric nerves, and the gastrointestinal microbiota. Adverse psychological factors contribute to persistent low-grade inflammation. The prognosis for patients with PI-IBS is somewhat better than for those with unselected IBS, but PI-IBS can still take years to resolve. There are no specific treatments for PI-IBS; these should be tailored to the predominant bowel disturbance, which is most frequently diarrhea.

Emphasis on the role of intestinal nervous system in the pathogenesis of inflammatory bowel disease

The etiology of inflammatory bowel disease, Crohn's disease and ulcerative colitis remains unknown. In a great many studies about the pathogenesis of IBD, great attention was paid to the immune dysfunction, genetic susceptibility, and various environmental factors, whereas the effects of enteric nervous system (ENS) were neglected. In fact, increasing evidence now indicates that ENS is involved in the pathogenesis of IBD. In this paper, we review the abnormal regulation of enteric nervous system in IBD.

Spatial and temporal expression of tachykinins and NK1- and NK2-receptor gene during TNB induced colitis in rats

The distribution and modification of the tachykinins Substance P (SP) and neurokinin A (NKA), their precursor beta-preprotachykinins (beta-PPT) and the receptors involved in their activity, NK-1 and NK-2, were studied in trinitrobenzensulphonic acid (TNB) colitis. Rats were intrarectally treated with a 120 mg/ml of TNB solution and sacrificed at various times after colitis induction. During the acute phases of colitis, a marked decrease in tissue SP and NKA levels were observed along with an increased transcription of beta-PPT mRNA in the neurons of the myenteric plexus and an increased myeloperoxidase activity, which is an index of the tissue's inflammatory status. De novo expression of both NK(1) and NK(2) receptor mRNA was observed during the acute phase of TNB-colitis in mesenchymal cells around dilated submucosal vessels but their expression in smooth muscle cells of the muscularis mucosae and propria was moderately down-regulated. The peptide levels, myeloperoxidase activity and gene expression of tachykinin receptors were then restored during the late phases (2-4 weeks after the apten administration) while beta-PPT mRNA remained highly expressed in the myenteric plexus ganglia showing that SP and NKA are involved in repair processes. These results point to the enhanced release of tachykinins during the initial phase of colitis and a restoration of this neuropeptide pool in the healing of the tissue.