Effect of transient chemically induced colitis on the visceromotor response to mechanical colorectal distension

Ojeok-san ameliorates visceral and somatic nociception in a mouse model of colitis induced colorectal cancer

Cancer patients can develop visceral, somatic, and neuropathic pain, largely due to the malignancy itself and its treatments. Often cancer patients and survivors turn to the use of complementary and alternative medicine (CAM) to alleviate pain and fatigue. Thus, it is necessary to investigate how CAM therapies work as novel analgesics to treat cancer pain. Ojeok-san (OJS) is an herbal formula consisting of seventeen herbs. This herbal formula has been shown to possess anti-inflammatory, immunoregulatory, and analgesic properties. In this study, we examined the potential beneficial effects and mechanism of action of OJS in a preclinical model of colitis-associated colorectal cancer. Male and female C57BL/6J mice were exposed to the carcinogen, azoxymethane (AOM, 10 mg/kg) and a chemical inflammatory driver, dextran sulfate sodium (DSS1-2%), to promote tumorigenesis in the colorectum. OJS was given orally (500, 1000, and 2000 mg/kg) to determine its influence on disease activity, tumor burden, nociception, sedation, Erk signaling, and behavioral and metabolic outcomes. In addition, in vitro studies were performed to assess CT-26 cell viability, dorsal root ganglia (DRG) activation, and bone-marrow-derived macrophage (BMDM) inflammatory response to lipopolysaccharide stimulation after OJS treatment. We found that administration of 2000 mg/kg of OJS was able to mitigate mechanical somatic and visceral nociception via Erk signaling without affecting symptom score and polyp number. Moreover, we discovered that OJS has sedative properties and elicits prolonged total sleeping time in AOM/DSS mice. Our in vitro experiments showed that OJS has the capacity to reduce TNFα gene expression in LPS-stimulated BMDM, but no changes were observed in DRG spike number and CT-26 cell proliferation. Taken together, these data suggest that OJS ameliorates nociception in mice and warrants further examination as a potential CAM therapy to promote analgesia.

Effect of estrogen on visceral sensory function in a non-inflammatory colonic hypersensitivity rat model

BACKGROUND

Increased prevalence of functional gastrointestinal disorders in women and perimenstrually accentuated symptoms imply that sexual hormones play a crucial role in the pathogenesis of such syndromes. The aim of this study was to analyze the selective effect of estrogen on visceral sensitivity in gonadectomized female and male Lewis rats with or without prior treatment with butyrate enemas.

METHODS

Following ovariectomy (OVX) or orchiectomy (ORX) estradiol pellets (E2-P) or sham pellets (Sham-P) were implanted. After treatment with butyrate (BUT) or saline (NaCl) enemas, colorectal distensions (CRD) were performed and the visceromotor reflex (VMR) to CRD was measured by electromyography.

KEY RESULTS

Gender did not influence VMR to CRD in gonadectomized animals. VMR in E2-P animals compared to Sham-P animals was increased (635 ± 32 μVs vs 470 ± 39 μVs; p = 0.002). Overall, instillation of butyrate enemas did not influence VMR to CRD. A comparison of CRD clusters showed that butyrate enemas in the E2-P animals resulted in a significant sensitization in both OVX and ORX animals. In female rats, sensitization was also caused by estrogen substitution alone.

CONCLUSION & INFERENCES

In our animal model, estrogen is a strong factor for an increase in visceral sensory function. Surprisingly, the treatment with butyrate alone did not evoke a general rise in VMR to CRD. Rats treated with butyrate enemas and under selective estrogen substitution developed visceral sensitization during the series of CRDs.

Activation of colo-rectal high-threshold afferent nerves by Interleukin-2 is tetrodotoxin-sensitive and upregulated in a mouse model of chronic visceral hypersensitivity

BACKGROUND

Chronic visceral pain is a defining feature of irritable bowel syndrome (IBS). IBS patients often show alterations in innate and adaptive immune function which may contribute to symptoms. Immune mediators are known to modulate the activity of viscero-sensory afferent nerves, but the focus has been on the innate immune system. Interleukin-2 (IL-2) is primarily associated with adaptive immune responses but its effects on colo-rectal afferent function in health or disease are unknown.

METHODS

Myeloperoxidase (MPO) activity determined the extent of inflammation in health, acute trinitrobenzene-sulfonic acid (TNBS) colitis, and in our post-TNBS colitis model of chronic visceral hypersensitivity (CVH). The functional effects of IL-2 on high-threshold colo-rectal afferents and the expression of IL-2R and NaV 1.7 mRNA in colo-rectal dorsal root ganglia (DRG) neurons were compared between healthy and CVH mice.

KEY RESULTS

MPO activity was increased during acute colitis, but subsided to levels comparable to health in CVH mice. IL-2 caused direct excitation of colo-rectal afferents that was blocked by tetrodotoxin. IL-2 did not affect afferent mechanosensitivity in health or CVH. However, an increased proportion of afferents responded directly to IL-2 in CVH mice compared with controls (73% vs 33%; p < 0.05), and the abundance of IL-2R and NaV 1.7 mRNA was increased 3.5- and 2-fold (p < 0.001 for both) in colo-rectal DRG neurons.

CONCLUSIONS & INFERENCES

IL-2, an immune mediator from the adaptive arm of the immune response, affects colo-rectal afferent function, indicating these effects are not restricted to innate immune mediators. Colo-rectal afferent sensitivity to IL-2 is increased long after healing from inflammation.

Mechanisms contributing to visceral hypersensitivity: focus on splanchnic afferent nerve signaling

BACKGROUND

Visceral hypersensitivity is a main characteristic of functional bowel disorders and is mediated by both peripheral and central factors. We investigated whether enhanced splanchnic afferent signaling in vitro is associated with visceral hypersensitivity in vivo in an acute and postinflammatory rat model of colitis.

METHODS

Trinitrobenzene sulfonic acid (TNBS)-colitis was monitored individually by colonoscopy to confirm colitis and follow convalescence and endoscopic healing in each rat. Experiments were performed in controls, rats with acute colitis and in postcolitis rats. Colonic afferent mechanosensitivity was assessed in vivo by quantifying visceromotor responses (VMRs), and by making extracellular afferent recordings from splanchnic nerve bundles in vitro. Multiunit afferent activity was classified into single units identified as low threshold (LT), wide dynamic range (WDR), high threshold (HT), and mechanically insensitive afferents (MIA).

KEY RESULTS

During acute TNBS-colitis, VMRs were significantly increased and splanchnic nerve recordings showed proportionally less MIA and increased WDR and HT afferents. Acute colitis gave rise to an enhanced spontaneous activity of both LT and MIA and augmented afferent mechanosensitivity in LT, WDR and HT afferents. Postcolitis, VMRs remained significantly increased, whereas splanchnic nerve recordings showed that the proportion of LT, WDR, HT and MIA had normalized to control values. However, LT and MIA continued to show increased spontaneous activity and WDR and HT remained sensitized to colorectal distension.

CONCLUSIONS & INFERENCES

Visceral hypersensitivity in vivo is associated with sensitized splanchnic afferent responses both during acute colitis and in the postinflammatory phase. However, splanchnic afferent subpopulations are affected differentially at both time points.

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.

A systematic review of the evidence for central nervous system plasticity in animal models of inflammatory-mediated gastrointestinal pain

BACKGROUND

Abdominal pain frequently accompanies inflammatory disorders of the gastrointestinal tract (GIT), and animal models of GIT inflammation have been developed to explore the role of the central nervous system (CNS) in this process. Here, we summarize the evidence from animal studies for CNS plasticity following GIT inflammation.

METHODS

A systematic review was conducted to identify studies that: (1) used inflammation of GIT organs, (2) assessed pain or visceral hypersensitivity, and (3) presented evidence of CNS involvement. Two hundred and eight articles were identified, and 79 were eligible for analysis.

RESULTS

Rats were most widely used (76%). Most studies used adult animals (42%) with a bias toward males (74%). Colitis was the most frequently used model (78%) and 2,4,6-trinitrobenzenesulfonic acid the preferred inflammatory agent (33%). Behavioral (58%), anatomical/molecular (44%), and physiological (24%) approaches were used alone or in combination to assess CNS involvement during or after GIT inflammation. Measurement times varied widely (<1 h-> 2 wk after inflammation). Blinded outcomes were used in 42% studies, randomization in 10%, and evidence of visceral inflammation in 54%. Only 3 studies fulfilled our criteria for high methodological quality, and no study reported sample size calculations.

CONCLUSIONS

The included studies provide strong evidence for CNS plasticity following GIT inflammation, specifically in the spinal cord dorsal horn. This evidence includes altered visceromotor responses and indices of referred pain, elevated neural activation and peptide content, and increased neuronal excitability. This evidence supports continued use of this approach for preclinical studies; however, there is substantial scope to improve study design.

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.

Neurological and cellular regulation of visceral hypersensitivity induced by chronic stress and colonic inflammation in rats

The role of inflammation in inducing visceral hypersensitivity (VHS) in ulcerative colitis patients remains unknown. We tested the hypothesis that acute ulcerative colitis-like inflammation does not induce VHS. However, it sets up molecular conditions such that chronic stress following inflammation exaggerates single-unit afferent discharges to colorectal distension. We used dextran sodium sulfate (DSS) to induce ulcerative colitis-like inflammation and a 9-day heterotypic chronic stress protocol in rats. DSS upregulated Nav1.8 mRNA in colon-responsive dorsal root ganglion (DRG) neurons, TRPV1 in colonic muscularis externae (ME) and BDNF in spinal cord without affecting the spike frequency in spinal afferents or VMR to CRD. By contrast, chronic stress did not induce inflammation but it downregulated Kv1.1 and Kv1.4 mRNA in DRG neurons, and upregulated TRPA1 and nerve growth factor in ME, which mediated the increase of spike frequency and VMR to CRD. Chronic stress following inflammation exacerbated spike frequency in spinal afferent neurons. TRPA1 antagonist suppressed the sensitization of afferent neurons. DSS-inflammation did not affect the composition or excitation thresholds of low-threshold and high-threshold fibers. Chronic stress following inflammation increased the percent composition of high-threshold fibers and lowered the excitation threshold of both types of fibers. We conclude that not all types of inflammation induce VHS, whereas chronic stress induces VHS in the absence of inflammation.

Psychological stress and the severity of post-inflammatory visceral hyperalgesia

OBJECTIVES

Lowered visceral sensory thresholds are a key finding in at least a subgroup of patients with functional bowel disorders. Stress and inflammation contribute to this altered visceral sensory function. We aimed to elucidate the role of repetitive stress and acute mucosal inflammation, alone and in combination, on sensory function.

METHODS

In randomized order, trinitrobenzenesulfonic acid (TNBS) plus the equal amount of ethanol or saline were instilled into the colorectum of female Lewis rats. Colorectal distensions (CRD) were performed with a barostat device (3 min/40 mmHg); to quantify the visceromotor response (VMR) to CRD, electromyographic activity (EMG) of the abdominal muscles was recorded. In randomized order, equal numbers of both treatment groups underwent either seven days (1 h/day) repetitive water avoidance stress (WAS) or sham WAS. CRD's were conducted 28 days later. Colonic tissue samples were obtained to characterize inflammation and blood samples were taken at day 28 to measure plasma IL-2 levels by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Compared to controls (662+/-114 microV) TNBS (1081+/-227 microV), WAS (1366+/-125 microV) and the combination of both (1477+/-390 microV) significantly augmented the VMR to CRD. TNBS and/or WAS caused significant inflammatory changes at day 5, while only TNBS+WAS also showed signs of mucosal inflammation on day 14 and significantly elevated IL-2 levels on day 28.

CONCLUSIONS

Stress and inflammation cause long lasting alterations of visceral sensory function. Concomitant stress further increases post-inflammatory visceral hyperalgesia.

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.

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.

A rat model of chronic postinflammatory visceral pain induced by deoxycholic acid

BACKGROUND & AIMS

Chronic visceral hyperalgesia is considered an important pathophysiologic symptom in irritable bowel syndrome (IBS); previous gastrointestinal inflammation is a potent etiologic factor for developing IBS. Although there are several animal models of adult visceral hypersensitivity after neonatal perturbation or acute colonic irritation/inflammation, current models of postinflammatory chronic visceral hyperalgesia are unsatisfactory. The aim of this study was to establish a model of chronic visceral hyperalgesia after colonic inflammation in the rat.

METHODS

Deoxycholic acid (DCA) was instilled into the rat colon daily for 3 days and animals were tested for up to 4 weeks.

RESULTS

DCA induced mild, transient colonic inflammation within 3 days that resolved within 3 weeks. An exaggerated visceromotor response, referred pain to mechanical stimulation, increased spinal Fos expression, and colonic afferent and dorsal horn neuron activity were apparent by 1 week and persisted for at least 4 weeks, indicating chronic dorsal horn hyperexcitability and visceral hyperalgesia. There was no spontaneous pain, based on open field behavior. There was a significant increase in opioid-receptor activity.

CONCLUSIONS

DCA induces mild, transient colitis, resulting in persistent visceral hyperalgesia and referred pain in rats, modeling some aspects of postinflammatory IBS.

Corticotropin-releasing hormone receptor 1 antagonist blocks colonic hypersensitivity induced by a combination of inflammation and repetitive colorectal distension

Gastroenteritis is one of the risk factors for developing irritable bowel syndrome (IBS). However, the precise mechanism of postinfectious IBS is still unknown. We tested the hypothesis that a combination of previous inflammation and repetitive colorectal distention (CRD) makes the colon hypersensitive and that treatment with a corticotropin-releasing hormone receptor 1 (CRH-R1) antagonist blocks this colonic hypersensitivity. Rats were pretreated with vehicle or 2,4,6-trinitrobenzene sulphonic acid (TNBS) 6 weeks before CRD. For the CRD experiment, the colorectum was distended once a day for six consecutive days. The CRH-R1 antagonist (CP-154,526, 20 mg kg(-1)) or vehicle was injected subcutaneously 30 min before CRD. Visceral perception was quantified as visceromotor response (VMR) using an electromyograph. For histological examination, the rats were killed on the last day of CRD experiment, and haematoxylin and eosin-staining of colon segments was performed. Although from the first to the third day of CRD, VMRs increased in both the vehicle-treated rats and TNBS-treated rats, they were significantly higher in TNBS-treated rats than those in vehicle-treated controls. On the fifth day of CRD, however, VMRs in the vehicle-treated rats were significantly greater than those in TNBS-treated rats. Pretreatment of rats with CP-154,526 significantly attenuated the increase in VMR induced by repetitive CRD with previous inflammation. Finally, we found that repetitive CRD and repetitive CRD after colitis induced visceral inflammation. These results indicate that a combination of previous inflammation and repetitive CRD induces visceral hypersensitivity and that a CRH-R1 antagonist attenuates this response in rats.

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.

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.

The role of transient receptor potential vanilloid 1 in mechanical and chemical visceral hyperalgesia following experimental colitis

The transient receptor potential vanilloid 1 receptor (TRPV1) is an important nociceptor involved in neurogenic inflammation. We aimed to examine the role of TRPV1 in experimental colitis and in the development of visceral hypersensitivity to mechanical and chemical stimulation. Male Sprague-Dawley rats received a single dose of trinitrobenzenesulfonic acid (TNBS) in the distal colon. In the preemptive group, rats received the TRPV1 receptor antagonist JYL1421 (10 mumol/kg, i.v.) or vehicle 15 min prior to TNBS followed by daily doses for 7 days. In the post-inflammation group, rats received JYL1421 daily for 7 days starting on day 7 following TNBS. The visceromotor response (VMR) to colorectal distension (CRD), intraluminal capsaicin, capsaicin vehicle (pH 6.7) or acidic saline (pH 5.0) was assessed in all groups and compared with controls and naïve rats. Colon inflammation was evaluated with H&E staining and myeloperoxidase (MPO) activity. TRPV1 immunoreactivity was assessed in the thoraco-lumbar (TL) and lumbo-sacral (LS) dorsal root ganglia (DRG) neurons. In the preemptive vehicle group, TNBS resulted in a significant increase in the VMR to CRD, intraluminal capsaicin and acidic saline compared the JYL1421-treated group (P<0.05). Absence of microscopic colitis and significantly reduced MPO activity was also evident compared with vehicle-treated rats (P<0.05). TRPV1 immunoreactivity in the TL (69.1+/-4.6%) and LS (66.4+/-4.2%) DRG in vehicle-treated rats was increased following TNBS but significantly lower in the preemptive JYL1421-treated group (28.6+/-3.9 and 32.3+/-2.3 respectively, P<0.05). JYL1421 in the post-inflammation group improved microscopic colitis and significantly decreased the VMR to CRD compared with vehicle (P<0.05, >/=30 mm Hg) but had no effect on the VMR to chemical stimulation. TRPV1 immunoreactivity in the TL and LS DRG was no different from vehicle or naïve controls. These results suggest an important role for TRPV1 channel in the development of inflammation and subsequent mechanical and chemical visceral hyperalgesia.

Experimental colitis modulates the functional properties of NMDA receptors in dorsal root ganglia neurons

N-methyl-D-aspartate (NMDA) receptors (NMDARs) on spinal afferent neurons regulate the peripheral and central release of neuropeptides involved in the development of hyperalgesia. We examined the effect of experimental colitis on the molecular and functional properties of NMDARs on these neurons. Lumbosacral dorsal root ganglia (DRG) were collected from adult rats 5 days after the induction of colitis for whole cell patch-clamp recording, Western blot analysis, and quantitative RT-PCR. Compared with neurons from control rats, those taken from animals with colitis had a threefold higher density of NMDA currents in both retrograde-labeled, colon-specific, and unlabeled DRG neurons. Increased current densities were not observed in DRG neurons taken from thoracic spinal levels. There was no significant change in NMDA or glycine affinity or in voltage-dependent Mg2+ inhibition; however, there was a 10-fold decrease in sensitivity to the NR2B subunit-selective antagonist ifenprodil. Quantitative RT-PCR and Western blot analysis indicated a 28% increase in the expression of NR2B with little or no change in the other three NR2 subunits. The addition of the Src family tyrosine kinase inhibitor PP2 (10 microM) decreased NMDAR currents in neurons from colitis but not control rats. Conversely, pretreatment of DRG neurons from control animals with 100 microM sodium orthovanadate increased NMDAR currents and decreased ifenprodil sensitivity to levels similar to those observed in neurons from animals with colitis. In conclusion, colonic inflammation upregulates the activity of NMDARs in all DRG neurons within ganglia innervating this tissue through mechanisms involving increased expression and persistent tyrosine phosphorylation.

Severity of mucosal inflammation as a predictor for alterations of visceral sensory function in a rat model

Transient inflammation is known to alter visceral sensory function and frequently precede the onset of symptoms in a subgroup of patients with irritable bowel syndrome (IBS). Duration and severity of the initial inflammatory stimulus appear to be risk factors for the manifestation of symptoms. Therefore, we aimed to characterize dose-dependent effects of trinitrobenzenesulfonic acid (TNBS)/ethanol on: (1) colonic mucosa, (2) cytokine release and (3) visceral sensory function in a rat model. Acute inflammation was induced in male Lewis rats by single administration of various doses of TNBS/ethanol (total of 0.8, 0.4 or 0.2 ml) in test animals or saline in controls. Assessment of visceromotor response (VMR) to colorectal distensions, histological evaluation of severity of inflammation, and measurement of pro-inflammatory cytokine levels (IL-2, IL-6) using enzyme-linked immunosorbent assay (ELISA) were performed 2h and 3, 14, 28, 31 and 42 days after induction. Increased serum IL-2 and IL-6 levels were evident prior to mucosal lesions 2h after induction of colitis and persist up to 14 days (p<0.05 vs. saline), although no histological signs of inflammation were detected at 14 days. In the acute phase, VMR was only significantly increased after 0.8 ml and 0.4 ml TNBS/ethanol (p<0.05 vs. saline). After 28 days, distension-evoked responses were persistently elevated (p<0.05 vs. saline) in 0.8 and 0.4 ml TNBS/ethanol-treated rats. In 0.2 ml TNBS/ethanol group, VMR was only enhanced after repeated visceral stimulation. Visceral hyperalgesia occurs after a transient colitis. However, even a mild acute but asymptomatic colitis can induce long-lasting visceral hyperalgesia in the presence of additional stimuli.

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.

Effect of DSS-induced colitis on visceral sensitivity to colorectal distension in mice

The present study aimed at evaluating the effect of dextran sodium sulphate (DSS)-induced colitis on visceral sensitivity, measured as the visceromotor response (VMR) to colorectal distension (CRD) in BALB/c and C57Bl/6 male mice. Inflammation was induced by the addition of 4% DSS to the drinking water for 5 (C57Bl/6) or 6-7 days (BALB/c). Parallel groups were used to monitor histopathological changes and visceral sensitivity. Pseudo-affective visceral pain responses were evoked using an increasing phasic CRD paradigm (10-60 mmHg) in conscious mice on predetermined days (pretreatment controls, 12, 16, 20, 30, 40 and 51). In both mouse strains, significant histopathological changes developed between days 2 and 5 of DSS treatment, and persisted until day 12 (P < 0.05). On day 15, inflammatory scores were reduced by about 50%. Despite evidence of inflammation in DSS-treated mice, no differences could be shown in the VMR to CRD between DSS-treated mice and controls at any time point tested. In addition, no differences were seen before and after DSS treatment in the same group of mice. In conclusion, these data suggest that DSS-induced colonic inflammation does not affect the visceral sensitivity to CRD, neither at short or long term, in BALB/c or C57Bl/6 male mice.

A combination of peppermint oil and caraway oil attenuates the post-inflammatory visceral hyperalgesia in a rat model

OBJECTIVE

Visceral hyperalgesia plays a pivotal role in manifestation of symptoms in patients with functional gastrointestinal disorders. In clinical studies combined treatment of peppermint- and caraway oil significantly reduced symptoms. Thus, the aim of this study was to characterize the effects of peppermint- and caraway oil, individually and in combination, on visceral nociception in a rat model of post-inflammatory visceral hyperalgesia.

MATERIAL AND METHODS

On day 28, male Lewis rats (n=80) were randomized to treatment with a rectal administration of trinitrobenzene sulphonic acid (TNBS)/ethanol or physiological saline solution. To quantify the visceromotor response to a standardized colorectal distension, bipolar electrodes were implanted into the external oblique musculature, just superior to the inguinal ligament for electromyographic recordings on day 3. On day 0, baseline measurement was performed. Thereafter, oral treatment with peppermint- or caraway oil or combination treatment was started and continued for 14 consecutive days. After 7 and 14 days of treatment a colorectal distension was performed. Colonic tissue samples were obtained on days 0, 7 and 14 to assess histological alterations due to the different treatment groups and the influence of different compounds.

RESULTS

After a single instillation of TNBS/ethanol persistent elevation of the visceromotor response at all different time-points was observed, although colonic mucosa was completely normal. After 14 days of combined treatment with peppermint- and caraway oil, a reduced visceromotor response of up to 50% compared to placebo was detected in TNBS/ethanol pretreated animals. In contrast, neither peppermint- nor caraway oil had a significant effect on post-inflammatory visceral hyperalgesia. In saline-treated controls there was no significant difference in the visceromotor response.

CONCLUSIONS

These data show that combined treatment with peppermint- and caraway oil modulates post-inflammatory visceral hyperalgesia synergistically. The exact mechanisms have to be further investigated.

Abdominaler Schmerz

Abdominal pain can result from a variety of different intra- and extra-abdominal disorders. Given the wide variety of etiological triggers for this pain, the primary task during the first stage of the diagnostic work-up is to determine as soon as possible the underlying cause and the degree of emergency. The aim of this evaluation is to adapt the therapeutic measures which are necessary for a causal treatment to the individual situation. Contrary to somatic causes of abdominal pain, the availability of such a causal therapy for functional bowel disorders is still very limited. Given this dilemma, the therapeutic focus of abdominal pain associated with these functional syndromes has to be placed on symptom-oriented treatment.

Pseudo-affective visceromotor responses and HPA axis activation following colorectal distension in rats with increased cholinergic sensitivity

We analysed visceromotor (VMR) and corticosterone responses to colorectal stimuli under control conditions and following acoustic stress in rats selectively bred for increased sensitivity to cholinergic agonists, the Flinders Sensitive Line (FSL) rats, compared with Flinders Resistant Line (FRL) rats. FSL rats demonstrated a significant VMR response at the smallest distension pressure, whereas no response was evident in FRL controls. FSL rats also demonstrated enhanced VMR responses at both larger distension levels compared with FRL rats. Colorectal distension (CRD) produced significant increases in serum corticosterone levels, which were comparable in FRL and FSL. Noise stress induced divergent corticosterone responses in FRL and FSL, but did not affect VMR to CRD in either group. These data suggest that FSL rats show altered VMR responses to CRD and disturbed hypothalamic-pituitary-adrenal axis responses to acute stress.