Psychological stress and the severity of post-inflammatory visceral hyperalgesia

The interaction between obesity and visceral hypersensitivity

Obesity has been a worldwide problem associated with numerous chronic diseases such as cardiovascular disease, type 2 diabetes, and metabolic disorders. It may also play a role in visceral hypersensitivity, contributing to irritable bowel syndrome. (i) Adipose tissue secretes various inflammatory mediators, causing intestinal hyperpermeability and nerve endings activation. (ii) Obesity and gastrointestinal microbiota could affect each other, and microbial metabolites can increase sensitivity of the colon. (iii) Vitamin D deficiency contributes to both fat accumulation and disruption of the intestinal mucosal barrier. (iv) Brain-gut axis may be another bridge from obesity to visceral hypersensitivity.

Chronic stress-associated visceral hyperalgesia correlates with severity of intestinal barrier dysfunction

In humans, chronic psychological stress is associated with increased intestinal paracellular permeability and visceral hyperalgesia, which is recapitulated in the chronic intermittent water avoidance stress (WAS) rat model. However, it is unknown whether enhanced visceral pain and permeability are intrinsically linked and correlate. Treatment of rats with lubiprostone during WAS significantly reduced WAS-induced changes in intestinal epithelial paracellular permeability and visceral hyperalgesia in a subpopulation of rats. Lubiprostone also prevented WAS-induced decreases in the epithelial tight junction protein, occludin (Ocln). To address the question of whether the magnitude of visceral pain correlates with the extent of altered intestinal permeability, we measured both end points in the same animal because of well-described individual differences in pain response. Our studies demonstrate that visceral pain and increased colon permeability positively correlate (0.6008, P = 0.0084). Finally, exposure of the distal colon in control animals to Ocln siRNA in vivo revealed that knockdown of Ocln protein inversely correlated with increased paracellular permeability and enhanced visceral pain similar to the levels observed in WAS-responsive rats. These data support that Ocln plays a potentially significant role in the development of stress-induced increased colon permeability. We believe this is the first demonstration that the level of chronic stress-associated visceral hyperalgesia directly correlates with the magnitude of altered colon epithelial paracellular permeability.

Pathophysiology of Functional Gastrointestinal Disorders: A Holistic Overview

Background and Summary: Traditionally, functional gastrointestinal disorders (FGID), including functional dyspepsia or irritable bowel syndrome (IBS), are defined by more or less specific symptoms and the absence of structural or biochemical abnormalities that cause these symptoms. This concept is now considered to be outdated; if appropriate tests are applied, structural or biochemical abnormalities that explain or cause the symptoms may be found in many patients. Another feature of FGID are the highly prevalent psychiatric comorbidities, such as depression and anxiety. It is implied that mood disorders "cause" gastrointestinal symptoms. In fact, epidemiological data now provide strong evidence that in subsets of cases, gastrointestinal (GI) symptoms arise first and mood disorders occur later, while in other patients the reverse appears to happen. Possible mechanisms for gut-brain dysfunction have been identified, with systemic minimal inflammation as a causal factor in at least some subjects. Other mechanisms that play a role in FGID include chronic infections, intestinal microbiota, low-grade mucosal inflammation including the increase of eosinophils, systemic immune activation, altered intestinal permeability, in diarrhea predominant IBS altered bile salt metabolism, abnormalities in the serotonin metabolism and genetic factors. All these factors might be modulated by environmental factors such as diet. Key Messages: While a number of factors can be linked to specific symptoms (e.g., pain or diarrhea), it is evident that the symptom-based categorization of patients will not allow targeted treatments that specifically address the underlying pathophysiology.

Effect of genetic background and postinfectious stress on visceral sensitivity in Citrobacter rodentium-infected mice

BACKGROUND

Infectious gastroenteritis is a major risk factor to develop postinfectious irritable bowel syndrome (PI-IBS). It remains unknown why only a subgroup of infected individuals develops PI-IBS. We hypothesize that immunogenetic predisposition is an important risk factor. Hence, we studied the effect of Citrobacter rodentium infection on visceral sensitivity in Th1-predominant C57BL/6 and Th2-predominant Balb/c mice.

METHODS

Eight-week-old mice were gavaged with C. rodentium, followed by 1 h of water avoidance stress (WAS) at 5 weeks PI. At 10, 14 days, and 5 weeks PI, samples were assessed for histology and inflammatory gene expression by RT-qPCR. Visceral sensitivity was evaluated by visceromotor response recordings (VMR) to colorectal distension.

KEY RESULTS

Citrobacter rodentium evoked a comparable colonic inflammatory response at 14 days PI characterized by increased crypt length and upregulation of Th1/Th17 cytokine mRNA levels (puncorrected  < 0.05) in both C57BL/6 and Balb/c mice. At 5 weeks PI, inflammatory gene mRNA levels returned to baseline in both strains. The VMR was maximal at 14 days PI in C57BL/6 (150 ± 47%; p = 0.02) and Balb/c mice (243 ± 52%; p = 0.03). At 3 weeks PI, the VMR remained increased in Balb/c (176 ± 23%; p = 0.02), but returned to baseline in C57BL/6 mice. At 5 weeks PI, WAS could not re-introduce visceral hypersensitivity (VHS).

CONCLUSIONS & INFERENCES

Citrobacter rodentium infection induces transient VHS in C57BL/6 and Balb/c mice, which persisted 1 week longer in Balb/c mice. Although other strain-related differences may contribute, a Th2 background may represent a risk factor for prolonged PI-VHS. As PI-VHS is transient, other factors are crucial for persistent VHS development as observed in PI-IBS.

Stress-induced visceral pain: toward animal models of irritable-bowel syndrome and associated comorbidities

Visceral pain is a global term used to describe pain originating from the internal organs, which is distinct from somatic pain. It is a hallmark of functional gastrointestinal disorders such as irritable-bowel syndrome (IBS). Currently, the treatment strategies targeting visceral pain are unsatisfactory, with development of novel therapeutics hindered by a lack of detailed knowledge of the underlying mechanisms. Stress has long been implicated in the pathophysiology of visceral pain in both preclinical and clinical studies. Here, we discuss the complex etiology of visceral pain reviewing our current understanding in the context of the role of stress, gender, gut microbiota alterations, and immune functioning. Furthermore, we review the role of glutamate, GABA, and epigenetic mechanisms as possible therapeutic strategies for the treatment of visceral pain for which there is an unmet medical need. Moreover, we discuss the most widely described rodent models used to model visceral pain in the preclinical setting. The theory behind, and application of, animal models is key for both the understanding of underlying mechanisms and design of future therapeutic interventions. Taken together, it is apparent that stress-induced visceral pain and its psychiatric comorbidities, as typified by IBS, has a multifaceted etiology. Moreover, treatment strategies still lag far behind when compared to other pain modalities. The development of novel, effective, and specific therapeutics for the treatment of visceral pain has never been more pertinent.

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.

Neuroplasticity and dysfunction after gastrointestinal inflammation

The gastrointestinal tract is innervated by several distinct populations of neurons, whose cell bodies either reside within (intrinsic) or outside (extrinsic) the gastrointestinal wall. Normally, most individuals are unaware of the continuous, complicated functions of these neurons. However, for patients with gastrointestinal disorders, such as IBD and IBS, altered gastrointestinal motility, discomfort and pain are common, debilitating symptoms. Although bouts of intestinal inflammation underlie the symptoms associated with IBD, increasing preclinical and clinical evidence indicates that infection and inflammation are also key risk factors for the development of other gastrointestinal disorders. Notably, a strong correlation exists between prior exposure to gut infection and symptom occurrence in IBS. This Review discusses the evidence for neuroplasticity (structural, synaptic or intrinsic changes that alter neuronal function) affecting gastrointestinal function. Such changes are evident during inflammation and, in many cases, long after healing of the damaged tissues, when the nervous system fails to reset back to normal. Neuroplasticity within distinct populations of neurons has a fundamental role in the aberrant motility, secretion and sensation associated with common clinical gastrointestinal disorders. To find appropriate therapeutic treatments for these disorders, the extent and time course of neuroplasticity must be fully appreciated.

The effect of chemically induced colitis, psychological stress and their combination on visceral pain in female Wistar rats

Visceral sensitivity is of pathophysiological importance in abdominal pain disorders and can be modulated by inflammation and stress. However, it is unclear whether inflammation and stress alter visceral perception independently of each other or in conjunction through neuroendocrine interactions. Therefore, we compared the short- and long-term effects of experimental colitis and water avoidance stress (WAS), alone or in combination, on visceral sensitivity in female Wistar rats. Colitis was induced by trinitrobenzene sulfonic acid (TNBS) and colonoscopically confirmed. During WAS, rats were placed on a platform surrounded by water for 1 h. Visceral sensitivity was assessed by quantifying the visceromotor responses (VMRs) to colorectal distension. Activation of the hypothalamic-pituitary-adrenal axis was determined by measuring serum corticosterone in a separate protocol. TNBS instillation resulted in overt colitis, associated with significant visceral hypersensitivity during the acute inflammatory phase (3 days post-TNBS; n = 8/group); after colitis had subsided (28 days post-TNBS), hypersensitivity was resolved (n = 4-8/group). Single WAS was associated with increased VMRs of a magnitude comparable to acute TNBS-induced hypersensitivity (n = 8/group). However, after repetitive WAS no significant hypersensitivity was present (n = 8/group). No additive effect of colitis and stress was seen on visceral pain perception (n = 6-8/group). Corticosterone levels were only increased in acute TNBS-colitis, acute WAS and their combination. To conclude, both colitis and stress successfully induced short-term visceral hypersensitivity and activated the hypothalamic-pituitary-adrenal axis, but long-term effects were absent. In addition, our current findings do not support an additive effect of colitis and stress on visceral sensitivity in female Wistar rats.

Effects of dominant/subordinate social status on formalin-induced pain and changes in serum proinflammatory cytokine concentrations in mice

Current investigations regarding social stress primarily focus on the health consequences of being in stressful social hierarchies. The repetitive nature of social conflicts seems to favor an induction of hyperalgesia or hypoalgesia, both in rodents and humans. Additionally, social conflicts may affect the immune system. In order to better establish the pain and immune responses to stress, the present study implemented a sensory contact model on 32 male BALB/c mice. Subsequent to establishing a dominance/submissive social relationship, each mouse was injected with formalin (20 μl, 2%) and their pain behavior was scored and serum concentrations of proinflammatory cytokines IL-1 and IL-6, and corticosterone were also measured. Test results revealed that subordinate mice were hypoalgesic during chronic phase of formalin test compared to control and dominant mice (P<0.05). On the other hand, subordinate mice were hyperalgesic compared to dominant mice during the whole acute phase of formalin test (P<0.05). Corticosterone, IL-1 and IL-6 concentrations were much higher in serum of dominant and subordinate mice than in the control group (p<0.05). The results indicated that, although both dominant and subordinate animals displayed an increase in serum corticosterone and proinflammatory cytokines during social interactions, their response to pain perception differently was affected with the social status.

Host immune response determines visceral hyperalgesia in a rat model of post-inflammatory irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is associated with visceral hyperalgesia and frequently occurs after a transient gastrointestinal infection. Only a proportion of patients with acute gastroenteritis develop post-infectious IBS suggesting differences in host response to inflammatory stimuli. We aimed to investigate this concept by characterizing visceral sensitivity in two rat strains, following a chemically induced colitis.

METHODS

Colorectal instillation of trinitrobenzenesulfonic acid (TNBS) in aqueous ethanol was used to induce a transient colitis in Lewis and F344 rats. The colitis was characterized semiquantitatively by histology, as well as by quantitative methods using (99m)Tc-leukocytes (radioactive organ assay) and plasma IL-2 and IL-6 levels. Visceromotor response to colorectal distensions was assessed after 2 h and, 5, 14, and 28 days.

RESULTS

The colitis peaked on day 5 and dissipated to no visible mucosal damage on day 14. Cytokines were significantly increased in TNBS-treated rats at 2 h and on day 5. On day 14 cytokines were still significantly enhanced in Lewis but not Fisher rats. Both strains had a highly inflamed to non-inflamed tissue ratio at 3 h after TNBS instillation with increased uptake in Lewis compared to F344 rats. No (99m)Tc-tin-colloid-leukocytes were detected in colon samples on day 28. Visceromotor response was significantly elevated in both strains during the acute colitis (day 5), whereas only Lewis rats developed a post-inflammatory (day 28) visceral hyperalgesia.

CONCLUSION

Genetically determined host factors account for prolonged immune activation in response to a standardized inflammatory stimulus and are linked to susceptibility for a post-inflammatory visceral hyperalgesia.

Alterations in prefrontal-limbic functional activation and connectivity in chronic stress-induced visceral hyperalgesia

Repeated water avoidance stress (WAS) induces sustained visceral hyperalgesia (VH) in rats measured as enhanced visceromotor response to colorectal distension (CRD). This model incorporates two characteristic features of human irritable bowel syndrome (IBS), VH and a prominent role of stress in the onset and exacerbation of IBS symptoms. Little is known regarding central mechanisms underlying the stress-induced VH. Here, we applied an autoradiographic perfusion method to map regional and network-level neural correlates of VH. Adult male rats were exposed to WAS or sham treatment for 1 hour/day for 10 days. The visceromotor response was measured before and after the treatment. Cerebral blood flow (CBF) mapping was performed by intravenous injection of radiotracer ([¹⁴C]-iodoantipyrine) while the rat was receiving a 60-mmHg CRD or no distension. Regional CBF-related tissue radioactivity was quantified in autoradiographic images of brain slices and analyzed in 3-dimensionally reconstructed brains with statistical parametric mapping. Compared to sham rats, stressed rats showed VH in association with greater CRD-evoked activation in the insular cortex, amygdala, and hypothalamus, but reduced activation in the prelimbic area (PrL) of prefrontal cortex. We constrained results of seed correlation analysis by known structural connectivity of the PrL to generate structurally linked functional connectivity (SLFC) of the PrL. Dramatic differences in the SLFC of PrL were noted between stressed and sham rats under distension. In particular, sham rats showed negative correlation between the PrL and amygdala, which was absent in stressed rats. The altered pattern of functional brain activation is in general agreement with that observed in IBS patients in human brain imaging studies, providing further support for the face and construct validity of the WAS model for IBS. The absence of prefrontal cortex-amygdala anticorrelation in stressed rats is consistent with the notion that impaired corticolimbic modulation acts as a central mechanism underlying stress-induced VH.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Chronic psychosocial stress induces reversible mitochondrial damage and corticotropin-releasing factor receptor type-1 upregulation in the rat intestine and IBS-like gut dysfunction

The association between psychological and environmental stress with functional gastrointestinal disorders, especially irritable bowel syndrome (IBS), is well established. However, the underlying pathogenic mechanisms remain unknown. We aimed to probe chronic psychosocial stress as a primary inducer of intestinal dysfunction and investigate corticotropin-releasing factor (CRF) signaling and mitochondrial damage as key contributors to the stress-mediated effects. Wistar-Kyoto rats were submitted to crowding stress (CS; 8 rats/cage) or sham-crowding stress (SC; 2 rats/cage) for up to 15 consecutive days. Hypothalamic-pituitary-adrenal (HPA) axis activity was evaluated. Intestinal tissues were obtained 1h, 1, 7, or 30 days after stress exposure, to assess neutrophil infiltration, epithelial ion transport, mitochondrial function, and CRF receptors expression. Colonic response to CRF (10 μg/kg i.p.) and hyperalgesia were evaluated after ending stress exposure. Chronic psychosocial stress activated HPA axis and induced reversible intestinal mucosal inflammation. Epithelial permeability and conductance were increased in CS rats, effect that lasted for up to 7 days after stress cessation. Visceral hypersensitivity persisted for up to 30 days post stress. Abnormal colonic response to exogenous CRF lasted for up to 7 days after stress. Mitochondrial activity was disturbed throughout the intestine, although mitochondrial response to CRF was preserved. Colonic expression of CRF receptor type-1 was increased in CS rats, and negatively correlated with body weight gain. In conclusion, chronic psychosocial stress triggers reversible inflammation, persistent epithelial dysfunction, and colonic hyperalgesia. These findings support crowding stress as a suitable animal model to unravel the complex pathophysiology underlying to common human intestinal stress-related disorders, such as IBS.

Pain intensity and duration can be enhanced by prior challenge: initial evidence suggestive of a role of microglial priming

Activation of spinal microglia and consequent release of proinflammatory mediators facilitate pain. Under certain conditions, responses of activated microglia can become enhanced. Enhanced microglial production of proinflammatory products may result from priming (sensitization), similar to macrophage priming. We hypothesized that if spinal microglia were primed by an initial inflammatory challenge, subsequent challenges may create enhanced pain. Here, we used a "two-hit" paradigm using 2 successive challenges, which affect overlapping populations of spinal microglia, presented 2 weeks apart. Mechanical allodynia and/or activation of spinal glia were assessed. Initially, laparotomy preceded systemic lipopolysaccharide (LPS). Prior laparotomy caused prolonged microglial (not astrocyte) activation plus enhanced LPS-induced allodynia. In this "two-hit" paradigm, minocycline, a microglial activation inhibitor, significantly reduced later exaggerated pain induced by prior surgery when minocycline was administered intrathecally for 5 days starting either at the time of surgery or 5 days before LPS administration. To test generality of the priming effect, subcutaneous formalin preceded intrathecal HIV-1 gp120, which activates spinal microglia and causes robust allodynia. Prior formalin enhanced intrathecal gp120-induced allodynia, suggesting that microglial priming is not limited to laparotomy and again supporting a spinal site of action. Therefore, spinal microglial priming may increase vulnerability to pain enhancement.

PERSPECTIVE

Spinal microglia may become "primed" (sensitized) following their activation by disparate forms of peripheral trauma/inflammation. As a result, such primed microglia may overrespond to subsequent challenges, thereby enhancing pain intensity and duration.

Small bowel homing T cells are associated with symptoms and delayed gastric emptying in functional dyspepsia

OBJECTIVES

Immune activation may have an important pathogenic role in the irritable bowel syndrome (IBS). While little is known about immunologic function in functional dyspepsia (FD), we have observed an association between cytokine secretion by peripheral blood mononuclear cells (PBMCs) and symptoms in IBS. Upper gastrointestinal inflammatory diseases are characterized by enhanced small bowel homing α4-, β7-integrin, chemokine receptor 9 (CCR9) positive T lymphocytes. We hypothesized that increased cytokine release and elevated circulating small bowel homing T cells are linked to the severity of symptoms in patients with FD. Thus, we aimed to (i) compare cytokine release in FD and healthy controls (HCs), (ii) quantify "gut homing" T cells in FD compared with HC and patients with IBS, and (iii) correlate the findings to symptom severity and gastric emptying.

METHODS

PBMC from 45 (Helicobacter pylori negative) patients with FD (Rome II) and 35 matched HC were isolated by density gradient centrifugation and cultured for 24 h. Cytokine production (tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-10) was measured by enzyme-linked immunosorbent assay. CD4+ α4β7+CCR9+ T cells were quantified by flow cytometry in FD, HC and 23 patients with IBS. Gastric emptying was measured by scintigraphy. Symptom severity was assessed utilizing the standardized Gastrointestinal Symptom Score.

RESULTS

FD patients had significantly higher TNF-α (107.2 ± 42.8 vs. 58.7 ± 7.4 pg/ml), IL-1β (204.8 ± 71.5 vs. 80.2 ± 17.4 pg/ml), and IL-10 (218 ± 63.3 vs. 110.9 ± 18.5 pg/ml) levels compared with HC, and enhanced gut homing lymphocytes compared with HC or IBS. Cytokine release and CD4+α4β7+CCR9+ lymphocytes were correlated with the symptom intensity of pain, cramps, nausea, and vomiting. Delayed gastric emptying was significantly associated (r = 0.78, P = 0.021) with CD4+α4β7+CCR9+ lymphocytes and IL-1β, TNF-α, and IL-10 secretion.

CONCLUSIONS

Cellular immune activation with increased small bowel homing T cells may be key factors in the clinical manifestations of H. pylori-negative FD.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Stress enhances muscle nociceptor activity in the rat

Chronic widespread pain, such as observed in irritable bowel (IBS) and fibromyalgia (FMS) syndrome, are markedly affected by stress. While such forms of stress-induced hyperalgesia are generally considered manifestations of "central sensitization," recent studies in patients with IBS and FMS suggest an additional, peripheral contribution. To examine the effect of stress on muscle nociceptor function, we evaluated activity in nociceptors innervating the gastrocnemius muscle in an animal model of chronic widespread pain, water avoidance stress, in the rat. This stressor, which produces mechanical hyperalgesia in skeletal muscle produced a significant decrease (∼34%) in mechanical threshold of muscle nociceptors and a marked, ∼two-fold increase in the number of action potentials produced by a prolonged (60 s) fixed intensity suprathreshold 10 g stimulus. Stress also induced an increase in conduction velocity from 1.25 m/s to 2.09 m/s, and increased variability in neuronal activity. Given that these changes, each of at least moderate magnitude, would be expected to enhance nociceptor activity, it is likely that, taken together, they contribute to the enhanced nociception observed in this model of stress-induced chronic widespread pain.

Further validation of a model of fibromyalgia syndrome in the rat

We have recently developed an animal model of fibromyalgia syndrome in the rat. In this model, rats exposed to unpredictable sound stress develop a delayed onset enhancement and prolongation of cytokine-induced mechanical hyperalgesia in muscle and skin. In this study, we tested the hypothesis that our model also manifests symptoms of common comorbid diagnoses: irritable bowel syndrome, temporomandibular disorder, and anxiety. Both visceral sensitivity and cytokine hyperalgesia in masseter muscle were present in the stressed rats. Furthermore, in an established model of irritable bowel syndrome-water avoidance-we observed significant muscle hyperalgesia. Finally, using the elevated plus maze to assess for anxiety level, we observed a significantly higher anxiety level in sound stress-exposed rats. Thus, unpredictable sound stress produces a condition in the rat with several features-delayed onset visceral and temporomandibular hyperalgesia and increased anxiety, as well as cutaneous and muscle hyperalgesia-commonly found in patients with fibromyalgia syndrome.

PERSPECTIVE

A stress model-unpredictable sound-in the rat exhibits several features (cutaneous, musculoskeletal, and visceral hyperalgesia, as well as anxiety) that are found in patients with fibromyalgia syndrome. Thus, this model may be used to test hypotheses about the underlying mechanisms and response to therapy in patients with fibromyalgia.

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.

Stress neuropeptides evoke epithelial responses via mast cell activation in the rat colon

BACKGROUND

Previously, we showed that corticotropin-releasing factor (CRF) injected i.p. mimicked epithelial responses to stress, both stimulating ion secretion and enhancing permeability in the rat colon, and mast cells were involved. However, the ability of CRF-sensitive mucosal/submucosal loops to regulate intestinal barrier and the participation of resident mast cells are unclear.

METHODS

We examined colonic epithelial responses to stress-like peptides in Wistar-Kyoto (WKY), and mast cell-deficient (Ws/Ws) and their +/+ littermate control rats in distal segments mounted in Ussing chambers. Short-circuit current (ion secretion), flux of horseradish peroxidase (macromolecular permeability), and the release of rat mast cell protease II were measured in response to CRF [10(-6) to 10(-8)M] or sauvagine [10(-8) to 10(-10)M] in tissues pretreated with astressin, doxantrazole, or vehicle.

RESULTS

Stress-like peptides (sauvagine > CRF) induced a dose-dependent increase in short-circuit current (maximal at 30 min), and significantly enhanced horseradish peroxidase flux and protease II release in WKY. Epithelial responses were inhibited by both astressin and doxantrazole, and significantly reduced in tissues from Ws/Ws rats.

CONCLUSION

The stress mediators CRF and sauvagine modulate barrier function in the rat colon acting on mucosal/submucosal CRF receptor-bearing cells, through mast cell-dependent pathways.

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.

Immune activation in patients with irritable bowel syndrome

BACKGROUND AND AIMS

We set out to test the hypothesis that irritable bowel syndrome (IBS) is characterized by an augmented cellular immune response with enhanced production of proinflammatory cytokines. We further aimed to explore whether symptoms and psychiatric comorbidity in IBS are linked to the release of proinflammatory cytokines.

METHODS

We characterized basal and Escherichia coli lipopolysaccharide (LPS)-induced cytokine production in peripheral blood mononuclear cells (PBMCs) from 55 IBS patients (18 mixed-, 17 constipation-, 20 diarrhea-predominant) and 36 healthy controls (HCs). PBMCs were isolated by density gradient centrifugation and cultured for 24 hours with or without (1 ng/mL) LPS. Cytokine production (tumor necrosis factor [TNF]-alpha, interleukin [IL]-1beta, and IL-6) was measured by enzyme-linked immunosorbent assay. Abdominal symptoms and psychiatric comorbidities were assessed by using the validated Bowel Disease Questionnaire and the Hospital Anxiety and Depression Scale.

RESULTS

IBS patients showed significantly (P < .017) higher baseline TNF-alpha, IL-1beta, IL-6, and LPS-induced IL-6 levels compared with HCs. Analyzing IBS subgroups, all cytokine levels were significantly (P < .05) higher in diarrhea-predominant IBS (D-IBS) patients, whereas constipation-predominant IBS patients showed increased LPS-induced IL-1beta levels compared with HCs. Baseline TNF-alpha and LPS-induced TNF-alpha and IL-6 levels were significantly higher in patients reporting more than 3 bowel movements per day, urgency, watery stools, and pain associated with diarrhea compared with patients without these symptoms (all P < .05). LPS-induced TNF-alpha production was associated significantly (r = 0.59, P < .001) with anxiety in patients with IBS.

CONCLUSIONS

Patients with D-IBS display enhanced proinflammatory cytokine release, and this may be associated with symptoms and anxiety.