Stress-induced Visceral Hypersensitivity Research Articles

Oxytocin inhibited stress induced visceral hypersensitivity, enteric glial cells activation, and release of proinflammatory cytokines in maternal separated rats

Visceral hypersensitivity (VH) is a significant contributor to irritable bowel syndrome (IBS). Oxytocin (OT) possesses analgesic effects on the central nervous system (CNS) and attenuates microglial activation, however, little is known about its peripheral effects and involvement in VH of IBS. Reactive enteric glial cells (EGCs) contributes to abnormal motility in gastrointestinal (GI) diseases. The aim of this study was to evaluate the peripheral use of OT to maintain VH and activation of EGCs through involvement of the Toll-like receptor (TLR) 4/MyD88/NF-κB signaling. After assessing a baseline visceromotor response (VMR) to colorectal distension (CRD), rats were exposed to a 1h water avoidance stress (WAS) session. Before each WAS session, intraperitoneal injection of OT (1mg/kg body weight, in phosphate-buffered saline (PBS)) atosiban (0.5mg/kg body weight, in PBS) or PBS (as a vehicle control, 1ml/kg body weight) was administered. Animas are killed 24h after the last WAS session. EGCs activity, relative OT receptor expression, glial fibrillary acidic protein (GFAP) expression and TLR4/MyD88/NF-κB signaling were evaluated. Neonatal maternal separation (MS) significantly increased the OT receptor expression and enhanced VMR to CRD. WAS improved VMR to CRD only during neonatal MS. OT treatment prevented WAS-induced higher VMRs to CRD, which was reversed by an OT receptor antagonist administration. Compared to the vehicle, OT pre-treated rats reduced EGCs activation, GFAP expression and TLR4/MyD88/NF-κB signaling. We conclude that neonatal MS induces VH and visceral pain in rats. Furthermore, exogenous OT attenuated stress-induced VH and EGCs activation, which was mediated by TLR4/MyD88/NF-κB signaling.

Effect of retrograde colonic electrical stimulation on colonic transit and stress-induced visceral hypersensitivity in rats with irritable bowel syndrome.

To evaluate the effects of retrograde colonic electrical stimulation (RCES) with trains of short pulses and RCES with long pulses on colonic transit in irritable bowel syndrome (IBS) rats and to investigate whether stress-induced visceral hypersensitivity could be alleviated by RCES so as to find a valuable new approach for IBS treatment. A total of 48 male rats were randomly divided into model group and control group. Visceral hypersensitivity model was induced by a 6-day HIS protocol composed of two stressors, restraint stress for 40min and forced swimming stress for 20min. The extent of visceral hypersensitivity was quantified by electromyography and abdominal withdrawal reflex scores (AWRs) of colorectal distension (use a balloon) at different pressures. After the modeling, all rats were equipped with electrodes in descending colon for retrograde electrical stimulation and a PE tube for perfusing phenol red saline solution in the ileocecus. After recovering from surgery, RCES with long pulses, RCES with trains of short pulses, and sham RCES were performed in colonic serosa of rats for 40min in six groups of 8 each, including three groups of visceral hypersensitivity rats and three groups of health rats. Colonic transit was assessed by calculating the output of phenol red from the anus every 10min for 90min. Finally, the extent of visceral hypersensitivity will be quantified again in model group. After the 6-day HIS protocol, the HIS rats displayed an increased sensitivity to colorectal distention, compared to control group at different distention pressures (P<0.01). CRES with trains of short pulses and long pulses significantly attenuated the hypersensitive responses to colorectal distention in the HIS rats compared with sham RCES group (P<0.01). The effects of RCES on rats colon transmission: In the IBS rats, the colonic emptying were (77.4±3.4)%, (74.8±2.4)% and (64.2±1.6)% in the sham RCES group, long pulses group and trains of short pulses group at 90min; In healthy rats, The colonic emptying was (65.2±3.5)%, (63.5±4.0)% and (54.0±2.5)% in the sham RCES group, long pulses group and trains of short pulses group at 90min. RCES with long pulses and RCES with trains of short pulses can significantly alleviate stress-induced visceral hypersensitivity. RCES with trains of short pulses has an inhibitory effect of colonic transit, both in visceral hypersensitivity rats and healthy rats.

Acute physical and psychological stress effects on visceral hypersensitivity in male rat: role of central nucleus of the amygdala

ObjectiveThe aim of this study was to investigate the effects of acute physical and psychological stress and temporary central nucleus of the amygdala (CeA) block on stress-induced visceral hypersensitivity. MethodsForty two male Wistar rats were used in this study. Animals were divided into 7 groups (n=6); 1 – Control, 2 – physical stress, 3 – psychological stress, 4 – sham, 5 – lidocaine, 6 – lidocaine+physical stress and 7 – lidocaine+psychological stress. Stress induction was done using a communication box. ResultsAbdominal withdrawal reflex (AWR) score was monitored one hour after stress exposure. AWR score significantly heightened at 20, 40 and 60mmHg in the psychological stress group compared with control (p<0.05), while, it was almost unchanged in other groups. This score was strikingly decreased at 20, 40 and 60mmHg in lidocaine+psychological stress group compared with psychological stress with no tangible response on physical stress. Total stool weight was significantly increased in psychological stress group compared with control (0.72±0.15, 0.1±0.06g) (p<0.05), but it did not change in physical stress compared to control group (0.16±0.12, 0.1±0.06g) (p<0.05). Concomitant use of lidocaine with stress followed the same results in psychological groups (0.18±0.2, 0.72±0.15g) (p<0.05), while it did not have any effect on physical stress group (0.25±0.1, 0.16±0.12g) (p<0.05). ConclusionsPsychological stress could strongly affect visceral hypersensitivity. This effect is statistically comparable with physical stress. Temporary CeA block could also reduce visceral hypersensitivity post-acute psychological stress.

Aminophylline suppresses stress-induced visceral hypersensitivity and defecation in irritable bowel syndrome

Pharmacological therapy for irritable bowel syndrome (IBS) has not been established. In order to find candidate drugs for IBS with diarrhea (IBS-D), we screened a compound library of drugs clinically used for their ability to prevent stress-induced defecation and visceral hypersensitivity in rats. We selected the bronchodilator aminophylline from this library. Using a specific inhibitor for each subtype of adenosine receptors (ARs) and phosphodiesterases (PDEs), we found that both A2BARs and PDE4 are probably mediated the inhibitory effect of aminophylline on wrap restraint stress (WRS)-induced defecation. Aminophylline suppressed maternal separation- and acetic acid administration-induced visceral hypersensitivity to colorectal distension (CRD), which was mediated by both A2AARs and A2BARs. We propose that aminophylline is a candidate drug for IBS-D because of its efficacy in both of stress-induced defecation and visceral hypersensitivity, as we observed here, and because it is clinically safe.

Sex differences in stress-induced visceral hypersensitivity following early life adversity: a two hit model.

Early life adversity (ELA) has been indicated as a risk factor for the development of stress axis dysfunction in adulthood, specifically in females. We previously showed that unpredictable ELA induces visceral hyperalgesia in adult female rats. It remains to be determined whether ELA alters visceral nociceptive responses to stress in adulthood. The current study tested the hypothesis that following ELA, exposure to an adulthood stressor, or second hit, serves as a risk factor for exaggerated stress-induced visceral hypersensitivity that is sex-specific. Following ELA, adult stress was induced via a single exposure (acute) or repetitive daily exposure, 1 h/day for 7 days (chronic), to water avoidance stress (WAS). Acute WAS increased pain behaviors in all adult female rats, however, females that experienced unpredictable ELA exhibited significantly more pain behaviors compared to those exposed to predictable ELA or controls. Following chronic WAS, all adult females exhibited increased pain responses, however, an exaggerated response was observed in rats exposed to unpredictable or predictable ELA compared to controls. Similarly, in adult male rats exposure to acute or chronic WAS increased pain behaviors, however, there were no differences in pain behaviors between ELA groups. This study highlights a novel consequence of ELA on stress-induced visceral nociception in adulthood that is sex-specific. More importantly, our study suggests that ELA not only serves as a risk factor for development of chronic pain in adulthood, but also serves as a predisposition for worsening of visceral pain following adult stress in female rats.

Role of 5-HT1A receptor in insular cortex mediating stress - induced visceral sensory dysfunction.

5-HT1A receptors (HTR1As) in the insular cortex are thought to be related with the generation of stress-induced functional gastrointestinal disorders (FGIDs), but its mechanism is not clear. Visceral hypersensitivity is one important pathophysiological mechanism of FGIDs. This study aimed to explore the role of HTR1As in mediating stress-induced visceral hypersensitivity and its mechanism in the insular cortex. Visceral hypersensitivity rat model was established by water avoidance stress (WAS) and the visceral sensitivity was measured by electromyogram. The activities of HTR1As were regulated by microinjecting the HTR1A agonist and antagonist into the insular cortex. The expression levels of 5-HT, HTR1A, N-methyl-d-aspartic acid receptor subtype 2B (NR2B) and c-fos were observed by RT-PCR, Western Blot and immunohistochemical staining. In WAS rats, the expression levels of 5-HT and HTR1As in the insular cortex were significantly lower (p < 0.05) than that in sham WAS and normal rats, but the levels of c-fos and NR2B were significantly higher (p < 0.05). After microinjecting HTR1As agonist into the insular cortex of WAS rats, the visceral sensitivity and the expression levels of NR2B and c-fos in insular cortex significantly decreased (p < 0.05). The HTR1As-NR2B signal pathway of insular cortex plays an important role in regulating stress-induced visceral hypersensitivity.

EXPRESS: Histone hyperacetylation modulates spinal type II metabotropic glutamate receptor alleviating stress-induced visceral hypersensitivity in female rats.

Stress is often a trigger to exacerbate chronic pain including visceral hypersensitivity associated with irritable bowel syndrome, a female predominant functional bowel disorder. Epigenetic mechanisms that mediate stress responses are a potential target to interfere with visceral pain. The purpose of this study was to examine the effect of a histone deacetylase inhibitor, suberoylanilide hydroxamic acid, on visceral hypersensitivity induced by a subchronic stressor in female rats and to investigate the involvement of spinal glutamate receptors. Three daily sessions of forced swim induced visceral hypersensitivity. Intrathecal suberoylanilide hydroxamic acid prevented or reversed the stress-induced visceral hypersensitivity, increased spinal histone 3 acetylation and increased mGluR2 and mGluR3 expression. Chromatin immunoprecipitation (ChIP) analysis revealed enrichment of H3K9Ac and H3K18Ac at several promoter Grm2 and Grm3 regions. The mGluR2/3 antagonist LY341495 reversed the inhibitory effect of suberoylanilide hydroxamic acid on the stress-induced visceral hypersensitivity. In surprising contrast, stress and/or suberoylanilide hydroxamic acid had no effect on spinal NMDA receptor expression or function. These data reveal histone modification modulates mGluR2/3 expression in the spinal cord to attenuate stress-induced visceral hypersensitivity. HDAC inhibitors may provide a potential approach to relieve visceral hypersensitivity associated with irritable bowel syndrome.

Estrogen-dependent visceral hypersensitivity following stress in rats: An fMRI study.

We used functional MRI and a longitudinal design to investigate the brain mechanisms in a previously reported estrogen-dependent visceral hypersensitivity model. We hypothesized that noxious visceral stimulation would be associated with activation of the insula, anterior cingulate cortex, and amygdala, and that estrogen-dependent, stress-induced visceral hypersensitivity would both enhance activation of these regions and recruit activation of other brain areas mediating affect and reward processing. Ovariectomized rats were treated with estrogen (17 β-estradiol, E2) or vehicle (n = 5 per group) and scanned in a 7T MRI at three different time points: pre-stress (baseline), 2 days post-stress, and 18 days post-stress. Stress was induced via a forced-swim paradigm. In a separate group of ovariectomized rats, E2 treatment induced visceral hypersensitivity at the 2 days post-stress time point, and this hypersensitivity returned to baseline at the 18 days post-stress time point. Vehicle-treated rats show no hypersensitivity following stress. During the MRI scans, rats were exposed to noxious colorectal distention. Across groups and time points, noxious visceral stimulation led to activations in the insula, anterior cingulate, and left amygdala, parabrachial nuclei, and cerebellum. A group-by-time interaction was seen in the right amygdala, ventral striatum-pallidum, cerebellum, hippocampus, mediodorsal thalamus, and pontine nuclei. Closer inspection of the data revealed that vehicle-treated rats showed consistent activations and deactivations across time, whereas estrogen-treated animals showed minimal deactivation with noxious visceral stimulation. This unexpected finding suggests that E2 may dramatically alter visceral nociceptive processing in the brain following an acute stressor. This study is the first to examine estrogen-stress dependent interactions in response to noxious visceral stimulation using functional MRI. Future studies that include other control groups and larger sample sizes are needed to fully understand the interactions between sex hormones, stress, and noxious stimulation on brain activity.

Early-life stress-induced visceral hypersensitivity and anxiety behavior is reversed by histone deacetylase inhibition.

Stressful life events, especially in childhood, can have detrimental effects on health and are associated with a host of psychiatric and gastrointestinal disorders including irritable bowel syndrome (IBS). Early-life stress can be recapitulated in animals using the maternal separation (MS) model, exhibiting many key phenotypic outcomes including visceral hypersensitivity and anxiety-like behaviors. The molecular mechanisms of MS are unclear, but recent studies point to a role for epigenetics. Histone acetylation is a key epigenetic mark that is altered in numerous stress-related disease states. Here, we investigated the role of histone acetylation in early-life stress-induced visceral hypersensitivity. Interestingly, increased number of pain behaviors and reduced threshold of visceral sensation were associated with alterations in histone acetylation in the lumbosacral spinal cord, a key region in visceral pain processing. Moreover, we also investigated whether the histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA), could reverse early-life stress-induced visceral hypersensitivity and stress-induced fecal pellet output in the MS model. Significantly, SAHA reversed both of these parameters. Taken together, these data describe, for the first time, a key role of histone acetylation in the pathophysiology of early-life stress-induced visceral hypersensitivity in a well-established model of IBS. These findings will inform new research aimed at the development of novel pharmaceutical approaches targeting the epigenetic machinery for novel anti-IBS drugs.

Specific alteration of rhythm in temperature-stressed rats possess features of abdominal pain in IBS patients

It is known that specific alteration of rhythm in temperature (SART) stress produces somatic pain. However, it remains to be investigated whether SART stress induces visceral pain. In this study, we investigated the visceral hypersensitivity in the SART stress model by pharmacological tools and heterotopical nociception. Four-week-old Sprague–Dawley rats were exposed to repeated cold stress. Visceral pain was measured by visceromotor response to colorectal distension, and the effects of alosetron and duloxetine on visceral pain were investigated in SART rats. Heterotopical nociception was given by capsaicin injection into the left forepaw to induce diffuse noxious inhibitory controls (DNIC). SART stress induced visceral hypersensitivity that was sustained at minimum for one week. In pharmacological analysis, alosetron and duloxetine improved SART stress-induced visceral hypersensitivity. Heterotopical nociception induced DNIC in normal conditions, but was disrupted in SART rats. On the other hand, RMCP-II mRNA in distal colon was not affected by SART stress. In conclusion, SART rats exhibit several features of visceral pain in IBS, and may be a useful model for investigating the central modification of pain control in IBS.

Dietary Marine n–3 PUFAs Do Not Affect Stress-Induced Visceral Hypersensitivity in a Rat Maternal Separation Model1–3

Background: Although never evaluated for efficacy, n–3 (ω-3) long-chain polyunsaturated fatty acids (LCPUFAs) are commercially offered as treatment for irritable bowel syndrome (IBS).Objective: This study was designed to investigate, in a mast cell–dependent model for visceral hypersensitivity, whether this pathophysiologic mechanism can be reversed by dietary LCPUFA treatment via peroxisome proliferator-activated receptor γ (PPARG) activationMethods: Maternally separated rats were subjected to hypersensitivity-inducing acute stress at adult age. Reversal was attempted by protocols with tuna oil–supplemented diets [4% soy oil (SO) and 3% tuna oil (SO–T3) or 3% SO and 7% tuna oil (SO–T7)] and compared with control SO diets (7% or 10% SO) 4 wk after stress. The PPARG agonist rosiglitazone was evaluated in a 1 wk preventive protocol (30 mg · kg−1 · d−1). Erythrocytes were assessed to confirm LCPUFA uptake and tissue expression of lipoprotein lipase and glycerol kinase as indicators of PPARG activation. Colonic mast cell degranulation was evaluated by toluidine blue staining. In vitro, human mast cell line 1 (HMC-1) cells were pretreated with rosiglitazone, eicosapentaenoic acid, or docosahexaenoic acid, stimulated with phorbol 12-myristate 13-acetate (PMA) and calcium ionophore or compound 48/80 and evaluated for tumor necrosis factor α (TNF-α) and β-hexosaminidase release.Results: Stress led to visceral hypersensitivity in all groups. Hypersensitivity was not reversed by SO–T3 or control treatment [prestress vs. 24 h poststress vs. posttreatment area under the curve; 76 ± 4 vs. 128 ± 12 (P < 0.05) vs. 115 ± 14 and 82 ± 5 vs. 127 ± 16 (P < 0.01) vs. 113 ± 19, respectively]. Comparison of SO–T7 with its control showed similar results [74 ± 6 vs. 103 ± 13 (P < 0.05) vs. 115 ± 17 and 66 ± 3 vs. 103 ± 10 (P < 0.05) vs. 117 ± 11, respectively]. Erythrocytes showed significant LCPUFA uptake in the absence of colonic PPARG activation. Rosiglitazone induced increased PPARG target gene expression, but did not prevent hypersensitivity. Mast cell degranulation never differed between groups. Rosiglitazone and LCPUFAs significantly reduced PMA/calcium ionophore–induced TNF-α release but not degranulation of HMC-1 cells.Conclusion: Dietary LCPUFAs did not reverse stress-induced visceral hypersensitivity in maternally separated rats. Although further research is needed, claims concerning LCPUFAs as a treatment option in IBS cannot be confirmed at this point and should be regarded with caution.

Role of the potassium chloride cotransporter isoform 2-mediated spinal chloride homeostasis in a rat model of visceral hypersensitivity.

Visceral hypersensitivity represents an important hallmark in the pathophysiology of irritable bowel syndrome (IBS), of which the mechanisms remain elusive. The present study was designed to examine whether cation-chloride cotransporter (CCC)-mediated chloride (Cl(-)) homeostasis of the spinal cord is involved in chronic stress-induced visceral hypersensitivity. Chronic visceral hypersensitivity was induced by exposing male Wistar rats to water avoidance stress (WAS). RT-PCR, Western blotting, and immunohistochemistry were used to assess the expression of CCCs in the spinal cord. Patch-clamp recordings were performed on adult spinal cord slices to evaluate Cl(-) homeostasis and Cl(-) extrusion capacity of lamina I neurons. Visceral sensitivity was estimated by measuring the abdominal withdrawal reflex in response to colorectal distension (CRD). After 10 days of WAS exposure, levels of both total protein and the oligomeric form of the K(+)-Cl(-) cotransporter isoform 2 (KCC2), but not Na(+)-K(+)-2Cl(-) transporter isoform 1 (NKCC1), were significantly decreased in the dorsal horn of the lumbosacral spinal cord. The downregulation of KCC2 resulted in a depolarizing shifted equilibrium potential of GABAergic inhibitory postsynaptic current and impaired Cl(-) extrusion capacity in lamina I neurons of the lumbosacral spinal cord from WAS rats. Acute noxious CRD disrupted spinal KCC2 expression and function 2 h after the final distention in sham rats, but not in WAS rats. Pharmacological blockade of KCC2 activity by intrathecal injection of a KCC2 inhibitor [(dihydroindenyl)oxy] alkanoic acid enhanced visceral nociceptive sensitivity in sham rats, but not in WAS rats. These results suggest that KCC2 downregulation-mediated impairment of spinal cord Cl(-) homeostasis may play an important role in chronic stress-induced visceral hypersensitivity.

P.1.h.034 Epigenetic reversal of early-life stress-induced visceral hypersensitivity and anxiety behaviour

Several lines of evidence indicate that early-life inflammation may predispose to mental illness, including depression, in later-life. We investigated the impact of perinatal exposure to polluted eels on neonatal, postnatal, and adult brain inflammation, and on the resignation behavior of male and female adult offspring mice. The effects of maternal standard diet (laboratory food) were compared to the same diet enriched with low, intermediate, or highly polluted eels. Brain inflammatory markers including cytokines were assessed in offspring mice on the day of birth (i.e., on the postnatal day–PND 1), upon weaning (PND 21) and at adulthood (PND 100). Plasma myeloperoxidase and corticosterone levels were evaluated at PND 100. Immobility behavior of offspring was assessed in adulthood (i.e., at PNDs 95–100), using the tail suspension and forced swimming tests. Chronic brain inflammation was found in male and female offspring mice compared to controls, as assessed at PNDs 1, 21, and 100. The level of myeloperoxidase was found to be significantly higher in both adult males and females vs. control offspring. However, high corticosterone levels were only found in male offspring mice that were perinatally exposed to eels, suggesting a gender-selective dysregulation of the adult hypothalamic-pituitaryadrenal (HPA) axis. Gender-specific differences were also detected in adulthood in regard to offspring resignation behavior. Thus, compared to controls, males, but not females, whose mothers were fed eels during pregnancy and lactation exhibited a depressive-like behavior in adult age in both behavioral models of depression. Depressive symptoms were more pronounced in male mice perinatally exposed to either intermediate or highly polluted eels than those exposed to only lowly polluted eels. Our results indicate that early-life inflammatory insult is a plausible causative factor that induces the depressive phenotype exhibited by male adult offspring mice, most likely through a gender-specific HPA axis enhanced activation.

76 Congenitally Elevated Gut Permeability Is Linked to Basal Visceral Hyposensitivity but Stress-Induced Visceral Hypersensitivity in CA-MLCK Mice

76 Congenitally Elevated Gut Permeability Is Linked to Basal Visceral Hyposensitivity but Stress-Induced Visceral Hypersensitivity in CA-MLCK Mice

Susceptibility to stress-induced visceral sensitivity: a bad legacy for next generations

Despite high prevalence, the precise irritable bowel syndrome (IBS) pathophysiology remains poorly understood likely due to the heterogeneity of IBS populations and the multifactorial etiology of this disorder. Among risk factors, genetic predisposition and early life trauma have been reported. In this context, the debate on genetic or environmental influences in the IBS pathogenesis is still open. The study by van der Wijngaard etal., reporting for the first time that susceptibility to stress-induced visceral hypersensitivity in maternally separated rats can be transferred to the next generation without any further exposure of F2 individuals to maternal separation, supports the importance of environmental influence in the IBS phenotype. Epigenetic mechanisms such as hypermethylation in the promoter region of the glucocorticoid receptor gene mediating the long-term and transgenerational behavioral effects of maternal care on the development have been shown in some but not in all studies. Van der Wijngaard etal. incriminated maternal care in the transmitted susceptibility to stress-induced visceral hypersensitivity, but not changes in glucocorticoid receptor protein expression in the brain. This finding opens a broad field of future directions aimed at evaluating the mechanisms involved in the transmission across generations of the digestive features of IBS, including, for example, on the role of gut microbiota changes in vertical transmission or epigenetic modifications of intestinal mast cells and the junctional region of intestinal epithelial cells in vertical transfer.

Toll-Like Receptor 4 Regulates Chronic Stress-Induced Visceral Pain in Mice

Functional gastrointestinal disorders, which have visceral hypersensitivity as a core symptom, are frequently comorbid with stress-related psychiatric disorders. Increasing evidence points to a key role for toll-like receptor 4 (TLR4) in chronic pain states of somatic origin. However, the central contribution of TLR4 in visceral pain sensation remains elusive. With pharmacological and genetic approaches, we investigated the involvement of TLR4 in the modulation of visceral pain. The TLR4-deficient and wild-type mice were exposed to chronic stress. Visceral pain was evaluated with colorectal distension. Protein expression levels for TLR4, Cd11b, and glial fibrillary acidic protein (glial cells markers) were quantified in the lumbar region of the spinal cord, prefrontal cortex (PFC), and hippocampus. To evaluate the effect of blocking TLR4 on visceral nociception, TAK-242, a selective TLR4 antagonist, was administered peripherally (intravenous) and centrally (intracerebroventricular and intra-PFC) (n = 10-12/experimental group). The TLR4 deficiency reduced visceral pain and prevented the development of chronic psychosocial stress-induced visceral hypersensitivity. Increased expression of TLR4 coupled with enhanced glia activation in the PFC and increased levels of proinflammatory cytokines were observed after chronic stress in wild-type mice. Administration of a TLR4 specific antagonist, TAK-242, attenuated visceral pain sensation in animals with functional TLR4 when administrated centrally and peripherally. Moreover, intra-PFC TAK-242 administration also counteracted chronic stress-induced visceral hypersensitivity. Our results reveal a novel role for TLR4 within the PFC in the modulation of visceral nociception and point to TLR4 as a potential therapeutic target for the development of drugs to treat visceral hypersensitivity.

Stress-Induced Visceral Hypersensitivity in Maternally Separated Rats Can Be Reversed by Peripherally Restricted Histamine-1-Receptor Antagonists

BackgroundThe histamine-1 receptor (H1R) antagonist ketotifen increased the threshold of discomfort in hypersensitive IBS patients. The use of peripherally restricted and more selective H1R antagonists may further improve treatment possibilities. We examined the use of fexofenadine and ebastine to reverse post-stress visceral hypersensitivity in maternally separated rats.MethodsThe visceromotor response to colonic distension was assessed in adult maternally separated and nonhandled rats pre- and 24 hours post water avoidance. Subsequently rats were treated with vehicle alone or different dosages of fexofenadine (1.8 and 18 mg/kg) or ebastine (0.1 and 1.0 mg/kg) and re-evaluated. Colonic tissue was collected to assess relative RMCP-2 and occludin expression levels by Western blot and histamine-1 receptor by RT-qPCR. β-hexosaminidase release by RBL-2H3 cells was used to establish possible mast cell stabilizing properties of the antagonists.Key resultsWater avoidance only induced enhanced response to distension in maternally separated rats. This response was reversed by 1.8 and 18 mg/kg fexofenadine. Reversal was also obtained by 1.0 but not 0.1 mg/kg ebastine. RMCP-2 expression levels were comparable in these two ebastine treatment groups but occludin was significantly higher in 1.0 mg/kg treated rats. There were no differences in histamine-1 receptor expression between nonhandled and maternally separated rats. Fexofenadine but not ebastine showed mast cell stabilizing quality.ConclusionsOur results indicate that the peripherally restricted 2nd generation H1-receptor antagonists fexofenadine and ebastine are capable of reversing post stress visceral hypersensitivity in rat. These data justify future IBS patient trials with these well tolerated compounds.

Gastrointestinal pain: Unraveling a novel endogenous pathway through uroguanylin/guanylate cyclase-C/cGMP activation

The natural hormone uroguanylin regulates intestinal fluid homeostasis and bowel function through activation of guanylate cyclase-C (GC-C), resulting in increased intracellular cyclic guanosine-3′,5′-monophosphate (cGMP). We report the effects of uroguanylin-mediated activation of the GC-C/cGMP pathway in vitro on extracellular cGMP transport and in vivo in rat models of inflammation- and stress-induced visceral hypersensitivity. In vitro exposure of intestinal Caco-2 cells to uroguanylin stimulated bidirectional, active extracellular transport of cGMP into luminal and basolateral spaces. cGMP transport was significantly and concentration dependently decreased by probenecid, an inhibitor of cGMP efflux pumps. In ex vivo Ussing chamber assays, uroguanylin stimulated cGMP secretion from the basolateral side of rat colonic epithelium into the submucosal space. In a rat model of trinitrobenzene sulfonic acid (TNBS)-induced visceral hypersensitivity, orally administered uroguanylin increased colonic thresholds required to elicit abdominal contractions in response to colorectal distension (CRD). Oral administration of cGMP mimicked the antihyperalgesic effects of uroguanylin, significantly decreasing TNBS- and restraint stress–induced visceromotor response to graded CRD in rats. The antihyperalgesic effects of cGMP were not associated with increased colonic spasmolytic activity, but were linked to significantly decreased firing rates of TNBS-sensitized colonic afferents in rats in response to mechanical stimuli. In conclusion, these data suggest that the continuous activation of the GC-C/cGMP pathway along the intestinal tract by the endogenous hormones guanylin and uroguanylin results in significant reduction of gastrointestinal pain. Extracellular cGMP produced on activation of GC-C is the primary mediator in this process via modulation of sensory afferent activity.

Mo2110 Assessment of Chymase Inhibition on Acute restraint Stress-Induced Visceral Hypersensitivity and Intestinal Dysfunction In Vivo.

Objective Intact anorectal function is integral to the maintenance of faecal continence. Anal ‘sampling' describes the process by which intermittent relaxation of the anal canal allows detection of rectal contents. Previous studies report such events to be subliminal; however data capture was limited by obsolete technology necessitating retrospective analysis. With the advent of high-resolution anorectal manometry (HRAM), this study aimed to re-evaluate the phenomenon of transient anal sphincter relaxations (TASRs) in healthy volunteers. Methods Twenty-one healthy volunteers (16 F;median age 34, range 22-69) without anorectal dysfunction underwent HRAM using a solid-state catheter incorporating 11 channels, spaced at 8 mm intervals. The study was performed in the sitting position for 45 minutes preand post consumption of a standardizedmeal (828 kcal; 48 g fat). Participants reported perception of any gastrointestinal / anorectal sensations in real-time. TASRs were defined as an equalization of rectal and anal pressures involving ≥20% of the anal canal. Characterization of anorectal pressures changes, event duration and association with perception were recorded. Statistical analysis utilized Wilcoxon matched pairs and Mann Whitney U tests. Results TASRs occurred more frequently following meal consumption (median 3 [IQR 1-6] vs. 0 [0-1]; P=0.01). Median TASR duration was 23 seconds [19-27] and involved a 44% reduction in average anal canal pressure (65 mmHg [53-81] before vs. 36 [28-44] during; P=0.0001). TASRs were accompanied by a 45% increase in rectal pressure (18 mmHg [15-23] before vs. 25 [19-33] during; P=0.001). Fifty-six percent were temporally associated with gastrointestinal / anorectal sensations, most commonly the urge to pass wind (74% perceived events). Perceived TASRs involved a greater length of the anal canal (62% of total length with perceived vs. 53% not perceived; P=0.005). Conclusion To the authors' knowledge, this is the first prolonged study of anorectal function usingHRAM. TASRs are uncommon preprandially and occur more frequently following meal consumption. Contrary to previous reports, the majority of TASRs are perceived, associated with the urge to pass wind. Alteration of TASR characteristics and relation to sensory perception may be important in the pathophysiology of colorectal disorders (e.g. incontinence); such studies, including the effect of intervention are ongoing.

Shugan-decoction relieves visceral hyperalgesia and reduces TRPV1 and SP colon expression

To evaluate the therapeutic effect of Shugan-decoction (SGD) on visceral hyperalgesia and colon gene expressions using a rat model. Ninety-six adult male Wistar rats were randomized into six equal groups for assessment of SGD effects on psychological stress-induced changes using the classic water avoidance stress (WAS) test. Untreated model rats were exposed to chronic (1 h/d for 10 d consecutive) WAS conditions; experimental treatment model rats were administered with intragastric SGD at 1 h before WAS on consecutive days 4-10 (low-dose: 0.1 g/mL; mid-dose: 0.2 g/mL; high-dose: 0.4 g/mL); control treatment model rats were similarly administered with the irritable bowel syndrome drug, dicetel (0.0042 g/mL); untreated normal control rats received no drug and were not subjected to the WAS test. At the end of the 10-d WAS testing period, a semi-quantitative measurement of visceral sensitivity was made by assessing the abdominal withdrawal reflex (AWR) to colorectal balloon-induced distension (at 5 mmHg increments) to determine the pain pressure threshold (PPT, evidenced by pain behavior). Subsequently, the animals were sacrificed and colonic tissues collected for assessment of changes in expressions of proteins related to visceral hypersensitivity (transient receptor potential vanilloid 1, TRPV1) and sustained visceral hyperalgesia (substance P, SP) by immunohistochemistry and real-time polymerase chain reaction. Inter-group differences were assessed by paired t test or repeated measures analysis of variance. The WAS test successfully induced visceral hypersensitivity, as evidenced by a significantly reduced AWR pressure in the untreated model group as compared to the untreated normal control group (190.4 ± 3.48 mmHg vs 224.0 ± 4.99 mmHg, P < 0.001). SGD treatments at mid-dose and high-dose and the dicetel treatment significantly increased the WAS-reduced PPT (212.5 ± 2.54, 216.5 ± 3.50 and 217.7 ± 2.83 mmHg respectively, all P < 0.001); however, the low-dose SGD treatment produced no significant effect on the WAS-reduced PPT (198.3 ± 1.78 mmHg, P > 0.05). These trends corresponded to the differential expressions observed for both TRPV1 protein (mid-dose: 1.64 ± 0.08 and high-dose: 1.69 ± 0.12 vs untreated model: 3.65 ± 0.32, P < 0.001) and mRNA (0.44 ± 0.16 and 0.15 ± 0.03 vs 1.39 ± 0.15, P < 0.001) and SP protein (0.99 ± 0.20 and 1.03 ± 0.23 vs 2.03 ± 0.12, P < 0.01) and mRNA (1.64 ± 0.19 and 1.32 ± 0.14 vs 2.60 ± 0.33, P < 0.05). These differential expressions of TRPV1 and SP related to mid- and high-dose SGD treatments were statistically similar to the changes induced by dicetel treatment. No signs of overt damage to the rat system were observed for any of the SGD dosages. Shugan-decoction can reduce chronic stress-induced visceral hypersensitivity in rats, and the regulatory mechanism may involve mediating the expressions of TRPV1 and SP in colon tissues.