Visceral Pain Hypersensitivity Research Articles

Sex differences in visceral sensitivity and brain activity in a rat model of comorbid pain: a longitudinal study.

Temporomandibular disorder (TMD) and irritable bowel syndrome (IBS) are 2 chronic overlapping pain conditions (COPCs) that present with significant comorbidity. Both conditions are more prevalent in women and are exacerbated by stress. While peripheral mechanisms might contribute to pain hypersensitivity for each individual condition, mechanisms underlying the comorbidity are poorly understood, complicating pain management when multiple conditions are involved. In this study, longitudinal behavioral and functional MRI-based brain changes have been identified in an animal model of TMD-like pain (masseter muscle inflammation followed by stress) that induces de novo IBS-like comorbid visceral pain hypersensitivity in rats. In particular, data indicate that increased activity in the insula and regions of the reward and limbic systems are associated with more pronounced and longer-lasting visceral pain behaviors in female rats, while the faster pain resolution in male rats may be due to increased activity in descending pain inhibitory pathways. These findings suggest the critical role of brain mechanisms in chronic pain conditions and that sex may be a risk factor of developing COPCs.

Sex Differences in Orofacial Sensitivity, Visceral Sensitivity, and Brain Activity in an Animal Model of Stress-induced Pain Hypersensitivity

Temporomandibular disorder (TMD) and irritable bowel syndrome (IBS) are two chronic overlapping pain conditions that present with significant comorbidity. Both conditions are more prevalent in women and are exacerbated by stress. While peripheral mechanisms might contribute to pain hypersensitivity for each individual condition, mechanisms underlying the comorbidity are poorly understood, complicating pain management when multiple conditions are involved. We hypothesize that changes in brain function initiated by pre-existing pain combined with stress contributes to development of de novo pain in susceptible individuals. Using an animal model (masseter muscle inflammation followed by stress) that induces de novo Comorbid visceral Pain Hypersensitivity (CPH) in rats, we reported more robust and longer duration CPH in female rats compared to males. The effects of stress alone (Stress-Induced Hypersensitivity, SIH) were examined. The relative percentage of male (9/12) and females (8/14) rats susceptible to stress (increased visceral pain one week post stress) was comparable. The stress resilient rats were excluded from further analysis of visceral pain. Preliminary data from both males and females showed SIH four weeks post stress, resolving by seven weeks in females (ANOVA, females p=.0250); data collection ongoing in males. Additional preliminary data show that stress alone increased orofacial mechanosensitivity in females (p=.0210, n=5), but not males (p=0.4, n=5). In the female cohort, the increased orofacial pain was only apparent in the susceptible females and not the resilient females. Analysis of functional connectivity using functional MRI is underway. Ultimately, changes in functional connectivity in SIH rats will be compared to CPH rats. This study supports our previous work using SIH and CPH groups, suggesting that hypersensitivity in males may resolve faster than in females. Grant support from NIDCR R01 DE029074.

Differential Activation of Colonic Afferents and Dorsal Horn Neurons Underlie Stress-Induced and Comorbid Visceral Hypersensitivity in Female Rats

Chronic Overlapping Pain Conditions, including irritable bowel syndrome (IBS) and temporomandibular disorder (TMD), represent a group of idiopathic pain conditions that likely have peripheral and central mechanisms contributing to their pathology, but are poorly understood. These conditions are exacerbated by stress and have a female predominance. The presence of one condition predicts the presence or development of additional conditions, making this a significant pain management problem. The current study was designed to determine if the duration and magnitude of peripheral sensitization and spinal central sensitization differs between restraint stress-induced visceral hypersensitivity (SIH) and chronic comorbid pain hypersensitivity (CPH; stress during pre-existing orofacial pain). SIH in female rats, as determined by the visceromotor response, persisted at least four but resolved by seven weeks. In contrast, CPH persisted at least seven weeks. Surprisingly, colonic afferents in both SIH and CPH rats were sensitized at seven weeks. CPH rats also had referred pain through seven weeks, but locally anesthetizing the colon only attenuated the referred pain through four weeks, suggesting a transition to colonic afferent independent central sensitization. Different phenotypes of dorsal horn neurons were sensitized in the CPH rats seven weeks post stress compared to four weeks or SIH rats. The current study suggests differential processing of colonic afferent input to the lumbosacral spinal cord contributes to visceral hypersensitivity during comorbid chronic pain conditions. PerspectiveChronic Overlapping Pain Conditions represent a unique challenge in pain management. The diverse nature of peripheral organs hinders a clear understanding of underlying mechanisms accounting for the comorbidity. This study highlights a mismatch between the condition-dependent behavior and peripheral and spinal mechanisms that contribute to visceral pain hypersensitivity.

Predisposition of Neonatal Maternal Separation to Visceral Hypersensitivity via Downregulation of Small-Conductance Calcium-Activated Potassium Channel Subtype 2 (SK2) in Mice.

Background Visceral hypersensitivity is a common occurrence of gastrointestinal diseases such as irritable bowel syndrome (IBS), wherein early-life stress (ELS) may have a high predisposition to the development of visceral hypersensitivity in adulthood, with the specific underlying mechanism still elusive. Herein, we assessed the potential effect of small-conductance calcium-activated potassium channel subtype 2 (SK2) in the spinal dorsal horn (DH) on the pathogenesis of visceral hypersensitivity induced by maternal separation (MS) in mice. Methods Neonatal mice were subjected to the MS paradigm, an established ELS model. In adulthood, the visceral pain threshold and the abdominal withdrawal reflex (AWR) were measured with an inflatable balloon. The elevated plus maze, open field test, sucrose preference test, and forced swim test were employed to evaluate the anxiety- and depression-like behaviors. The expression levels of SK2 in the spinal DH were determined by immunofluorescence and western blotting. The mRNA of SK2 and membrane palmitoylated protein 2 (MPP2) were determined by quantitative real-time polymerase chain reaction (qRT-PCR). Electrophysiology was applied to evaluate the neuronal firing rates and SK2 channel-mediated afterhyperpolarization current (IAHP). The interaction between MPP2 and SK2 was validated by coimmunoprecipitation. Results In contrast to the naïve mice, ethological findings in MS mice revealed lowered visceral pain threshold, more evident anxiety- and depression-like behaviors, and downregulated expression of membrane SK2 protein and MPP2 protein. Moreover, electrophysiological results indicated increased neuronal firing rates and decreased IAHP in the spinal DH neurons. Nonetheless, intrathecal injection of the SK2 channel activator 1-ethyl-2-benzimidazolinone (1-EBIO) in MS mice could reverse the electrophysiological alterations and elevate the visceral pain threshold. In the naïve mice, administration of the SK2 channel blocker apamin abated IAHP and elevated spontaneous neuronal firing rates in the spinal DH neurons, reducing the visceral pain threshold. Finally, disruption of the MPP2 expression by small interfering RNA (siRNA) could amplify visceral hypersensitivity in naïve mice. Conclusions ELS-induced visceral pain and visceral hypersensitivity are associated with the underfunction of SK2 channels in the spinal DH.

Transcutaneous vagus nerve stimulation prevents the development of, and reverses, established oesophageal pain hypersensitivity.

The vagus nerve exerts an anti-nociceptive effect on the viscera. To investigate whether transcutaneous vagal nerve stimulation (t-VNS) prevents the development of and/or reverses established visceral hypersensitivity in a validated model of acid-induced oesophageal pain. Before and after a 30-minute infusion of 0.15M hydrochloric acid into the distal oesophagus, pain thresholds to electrical stimulation were determined in the proximal non-acid exposed oesophagus. Validated sympathetic (cardiac sympathetic index) and parasympathetic (cardiac vagal tone [CVT]) nervous system measures were recorded. In study 1, 15 healthy participants were randomised in a blinded crossover design to receive either t-VNS or sham for 30minutes during acid infusion. In study 2, 18 different healthy participants were randomised in a blinded crossover design to receive either t-VNS or sham, for 30minutes after acid infusion. Study 1: t-VNS increased CVT (31.6% ± 58.7 vs -9.6±20.6, P=0.02) in comparison to sham with no effect on cardiac sympathetic index. The development of acid-induced oesophageal hypersensitivity was prevented with t-VNS in comparison to sham (15.5mA per unit time (95% CI 4.9 - 26.2), P=0.004). Study 2: t-VNS increased CVT (26.3% ± 32.7 vs 3±27.1, P=0.03) in comparison to sham with no effect on cardiac sympathetic index. t-VNS reversed established acid-induced oesophageal hypersensitivity in comparison to sham (17.3mA/unit time (95% CI 9.8-24.7), P=0.0001). t-VNS prevents the development of, and reverses established, acid-induced oesophageal hypersensitivity. These results have therapeutic implications for the management of visceral pain hypersensitivity.

Peripheral mechanisms contribute to comorbid visceral hypersensitivity induced by preexisting orofacial pain and stress in female rats.

BackgroundStress exacerbates many chronic pain syndromes including irritable bowel syndrome (IBS). Among these patient populations, many suffer from comorbid or chronic overlapping pain conditions and are predominantly female. Nevertheless, basic studies investigating chronic psychological stress‐induced changes in pain sensitivity have been mostly carried out in male rodents. Our laboratory developed a model of comorbid pain hypersensitivity (CPH) (stress in the presence of preexisting orofacial pain inducing chronic visceral pain hypersensitivity that significantly outlasts transient stress‐induced pain hypersensitivity (SIH)) facilitating the study of pain associated with IBS. Since CPH and SIH are phenotypically similar until SIH resolves and CPH persists, it is unclear if underlying mechanisms are similar.MethodsIn the present study, the visceromotor response (VMR) to colorectal distention was recorded in the SIH and CPH models in intact females and ovariectomized rats plus estradiol replacement (OVx + E2). Over several months, rats were determined to be susceptible or resilient to stress and the role of peripheral corticotrophin‐releasing factor (CRF) underlying in the pain hypersensitivity was examined.Key ResultsStress alone induced transient (3‐4 weeks) visceral hypersensitivity, though some rats were resilient. Comorbid conditions increased susceptibility to stress prolonging hypersensitivity beyond 13 weeks. Both models had robust peripheral components; hypersensitivity was attenuated by the CRF receptor antagonist astressin and the mast cell stabilizer disodium cromoglycate (DSCG). However, DSCG was less effective in the CPH model compared to the SIH model.Conclusions and InferencesThe data indicate many similarities but some differences in mechanisms contributing to comorbid pain conditions compared to transient stress‐induced pain.

Targeting spinal TRAF6 expression attenuates chronic visceral pain in adult rats with neonatal colonic inflammation.

BackgroundIrritable bowel syndrome is one of the most common gastrointestinal disorders. It is featured by abdominal pain in conjunction with altered bowel habits. However, the pathophysiology of the syndrome remains largely unknown. Tumor necrosis factor receptor-associated factor 6 (TRAF6) has been reported to be involved in neuropathic pain. The aim of this study was to investigate roles and mechanisms of TRAF6 in the chronic visceral hypersensitivity.MethodsVisceral hypersensitivity was induced by neonatal colonic inflammation and was identified by colorectal distention. The protein level, RNA level, and cellular distribution of TRAF6 and its related molecules were detected with Western blot, quantitative polymerase chain reaction, and immunofluorescence. In vitro spinal cord slice recording technique was performed to determine the synaptic transmission activities.ResultsNeonatal colonic inflammation rats displayed visceral hypersensitivity at the age of six weeks. The expression of TRAF6 was obviously upregulated in spinal cord dorsal horn of neonatal colonic inflammation rats at the age of six weeks. Immunofluorescence study showed that TRAF6 was dominantly expressed in spinal astrocytes. Intrathecal injection of TRAF6 small interfering RNA (siRNA) significantly reduced the amplitude of spontaneous excitatory postsynaptic currents at the spinal dorsal horn level. Furthermore, knockdown of TRAF6 led to a significant downregulation of cystathionine β synthetase expression in the spinal dorsal horn of neonatal colonic inflammation rats. Importantly, intrathecal injection of TRAF6 siRNA remarkably alleviated visceral hypersensitivity of neonatal colonic inflammation rats.ConclusionsOur results suggested that the upregulation of TRAF6 contributed to visceral pain hypersensitivity, which is likely mediated by regulating cystathionine β synthetase expression in the spinal dorsal horn. Our findings suggest that TRAF6 might act as a potential target for the treatment of chronic visceral pain in irritable bowel syndrome patients.

Gastrointestinal disorders-induced pain

Functional gastrointestinal disorders (FGIDs), now better defined as disorders of gut-brain interaction (DGBI) are disorders of gut-brain interaction. Chronic episodic abdominal pain and discomfort constitute integral diagnostic criteria of these disorders. A common feature of these disorders is heightened pain sensitivity to experimental gut stimulation, termed visceral pain hypersensitivity (VPH). Visceral pain disorders are a tremendous health care burden; continues to pose a significantly unmet medical need, negatively affecting the lives of millions of individuals worldwide in all ethnic groups and all economic classes. The origin and maintenance of visceral pain involves peripheral and central mechanisms. In this review, we have highlighted the roles of the Microbiota, Nerve growth factor (NGF), NLRP3 inflammasome and vascular endothelial growth factor (VEGF) and tried to address the potential for manipulating these as a therapeutic target for FGIDs associated with visceral pain hypersensitivity which may warrant for drug development in the future.

Analgesic effect of resveratrol on colitis-induced visceral pain via inhibition of TRAF6/NF-κB signaling pathway in the spinal cord

Visceral pain is a complex and common symptom of inflammatory bowel disease (IBD) patients. Developing novel efficient therapeutics is still a common interest for clinicians. Increasing evidence have shown that tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6) contributes to the pathological pain state in some pain models. Resveratrol (RSV) has showed promising potential for the treatment of neuropathic pain and inflammatory pain. However, whether RSV has analgesic effect on visceral pain and the underlying mechanisms remain unclear. In this study, we established the colitis model through intrarectal administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS), and found that TNBS induced colonic inflammation and visceral hypersensitivity. Meanwhile, astroglial marker glial fibrillary acidic protein (GFAP), TRAF6, phosphorylation of NF-κB (pNF-κB), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) levels were increased in L6-S1 spinal cord after TNBS enema. Then, intrathecal injection of TRAF6 siRNA attenuated visceral pain, blocked the upregulation of pNF-κB, TNF-α and IL-1β levels in the spinal cord in TNBS mice. Furthermore, spinal administration of NF-κB inhibitor, BAY11-7082 reversed the pain behavior and suppressed spinal TNF-α and IL-1β expression in TNBS mice. Finally, repeated intrathecal injection of RSV reversed TNBS-induced visceral pain hypersensitivity in a dose-dependent manner. Meanwhile, TNBS-induced enhancement of spinal GFAP, TRAF6, pNF-κB, TNF-α and IL-1β were reduced by the same treatment of RSV. In conclusion, our results suggest that RSV exerts the effects of antinociception on colitis-induced visceral hyperalgesia through inhibition of spinal TRAF6/NF-κB signaling pathway and the production of inflammatory mediators in the spinal cord, suggesting a new application of RSV for the treatment of visceral pain.

Identification of experimental bladder sensitivity among dysmenorrhea sufferers

Dysmenorrhea is a common risk factor for chronic pain conditions including bladder pain syndrome. Few studies have formally evaluated asymptomatic bladder pain sensitivity in dysmenorrhea, and whether this largely reflects excess pelvic symptom reporting due to comorbid psychological dysfunction. We sought to determine whether bladder hypersensitivity is more common among women reporting moderate or greater dysmenorrhea, without chronic pain elsewhere, after accounting for anxiety and depression. Demonstrating this would suggest that dysmenorrhea might be an early clue for visceral or widespread pain hypersensitivity and improve understanding of potential precursors to bladder pain syndrome. We compared cohorts of regularly menstruating women, without symptoms of chronic pain elsewhere, reporting (1) moderate-to-severe dysmenorrhea (n= 98) and (2) low levels or no menstrual pain (n= 35). Participants underwent rapid bladder filling following a standard water ingestion protocol, serially rating bladder pain and relative urgency during subsequent distension. Potential differences in bladder volumes were controlled for by sonographic measurement at standard cystometric thresholds. Bladder sensitivity was also measured with complementary measures at other times separately including a simplified rapid filling test, palpation of the bladder wall, and through ambulatory self-report. Anxiety and depression were evaluated with the National Institutes of Health Patient-Reported Outcomes Measurement Information System measures. Women with moderate-to-severe dysmenorrhea reported more urinary symptoms than controls and had a lower maximum capacity (498 ± 18 mL vs 619 ± 34 mL, P < .001) and more evoked bladder filling pain (0-100 visual analog scale: 25 ± 3 vs 12 ± 3, P < .001). The dysmenorrhea-bladder capacity relationship remained significant irrespective of menstrual pain severity, anxiety, depression, or bladder pain (R2= 0.13, P= .006). Severity of menstrual pain predicted evoked bladder pain (R2= 0.10, P= .008) independent of anxiety (P= .21) and depression (P= .21). Women with moderate-to-severe dysmenorrhea exhibiting provoked bladder pain (24/98, 24%) also reported higher pain during the screening rapid bladder test (P < .001), in response to transvaginal bladder palpation (P < .015), and on prospective daily diaries (P < .001) than women with dysmenorrhea without provoked bladder pain. Women experiencing moderate-to-severe dysmenorrhea also harbor a higher pain response to naturally evoked bladder distension. Noninvasive bladder provocation needs to be tested furtherlongitudinally in those with dysmenorrhea to characterize the course of visceral sensitivity and determine if it may help predict individuals at risk for developing subsequent pain in the bladder or elsewhere.

MicroRNA-146a-5p attenuates visceral hypersensitivity through targeting chemokine CCL8 in the spinal cord in a mouse model of colitis

Visceral pain, observed in inflammatory bowel disease (IBD) patients, is a challenging medical problem and remains poorly understood because the mechanisms underlying it are unclear. Emerging evidence indicates that microRNAs (miRNAs) play a crucial role in the pathogenesis of acute and chronic pain. In this study, we aimed to explore the potential role of miR-146a-5p (the mature form of miR-146a) in a mouse model of colitis induced by intracolonic injection of trinitrobenzene sulfonic acid (TNBS). We found that induction of colitis resulted in visceral hyperalgesia manifested by a decreased pain threshold to colorectal distension and upregulation of miR-146a-5p expression in the lumbosacral spinal cord. In situ hybridization and immunohistochemistry results showed that miR-146a-5p was colocalized with neuronal marker NeuN, but not with astrocytic marker GFAP or microglial marker IBA-1. Dual-luciferase reporter assay showed that miR-146a-5p directly targeted the 3′-untranslated region (UTR) of CCL8, which was previously identified as an important regulator of visceral pain. In cultured Neuro-2a cells, TNF-α-induced CCL8 upregulation was decreased by transfection of miR-146a-5p mimic dose-dependently. In vivo, exogenous supplementation of miR-146a-5p by intrathecal miR-146a-5p agomir significantly alleviated visceral pain and decreased CCL8 expression in colitis mice. Furthermore, inhibition of CCL8 expression by CCL8 siRNA relieved colitis-induced visceral nociception. Finally, in naïve mice intrathecal miR-146a-5p antagomir upregulated CCL8 expression and induced visceral pain hypersensitivity, which could be partially rescued by neutralization of CCL8. Taken together, the present findings indicate that miR-146a-5p may be an endogenous suppressor of visceral pain and exogenous supplementation of miR-146a-5p could exert an analgesic effect at least partly by targeting spinal CCL8 expression. Thus, miR-146a-5p may serve as a novel therapeutic target for visceral pain intervention in the context of colitis.

Differential modulation of voltage-gated sodium channels by nerve growth factor in three major subsets of TrkA-expressing nociceptors.

Nerve growth factor is an inflammatory mediator that induces long-lasting hyperalgesia, which can partially be attributed to nerve growth factor-induced sensitization of primary afferent nociceptors. It was shown that nerve growth factor increases the excitability of polymodal C-fibre nociceptors by modulating tetrodotoxin-sensitive and tetrodotoxin-resistant voltage-gated sodium channels, but hitherto only little is known about the effects of nerve growth factor on sodium currents in other nociceptor subtypes that express the nerve growth factor receptor TrkA. We previously characterized two reporter mouse lines that allow the unequivocal identification of two important subclasses of TrkA-expressing nociceptors – i.e. neuropeptide Y receptor type 2 (NPY2R+ ) Aδ-fibre nociceptors that mediate pinprick pain and nicotinic acetylcholine receptor alpha-3 subunit (CHRNA3+ ) silent nociceptors, which are the most abundant TrkA+ nociceptors in visceral organs and deep somatic tissues. Here, we utilized these mouse lines to investigate the expression patterns and the possible nerve growth factor-dependent modulation of sodium channels in these neurons using whole-cell patch-clamp recordings and quantitative real-time polymerase chain reaction. We demonstrate that NPY2R+ nociceptors, CHRNA3+ ‘silent’ nociceptors and polymodal C-fibre nociceptors express different combinations of sodium channel α- and β-subunits and accordingly exhibit functionally different sodium currents. Moreover, we demonstrate that nerve growth factor produces robust hyperpolarizing shifts in the half-activation voltage of tetrodotoxin-resistant currents in NPY2R+ nociceptors and polymodal C-fibre nociceptors and also shifts the half-activation of tetrodotoxin-sensitive currents in polymodal C-fibre nociceptors. In silent nociceptors, however, nerve growth factor solely increases the current density of the tetrodotoxin-resistant current but does not alter other sodium channel properties. Considering the different peripheral target tissues and the previously reported roles in different forms of pain of the nociceptor subpopulations that were examined here, our results suggest that nerve growth factor differentially contributes to the development visceral and cutaneous pain hypersensitivity and highlights the importance of developing different therapeutic strategies for different forms of pain.

Central and Peripheral Modulation of Visceral Pain and Visceral Hypersensitivity by the CRF-CRFR System

Central and Peripheral Modulation of Visceral Pain and Visceral Hypersensitivity by the CRF-CRFR System

Zeta Inhibitory Peptide as a Novel Therapy to Control Chronic Visceral Hypersensitivity in a Rat Model.

BackgroundThe pathogenesis of multiple chronic visceral pain syndromes, such as irritable bowel syndrome (IBS), is not well known, and as a result current therapies are ineffective. The objective of this study was to investigate the effect of spinal protein kinase M zeta (PKMζ) on visceral pain sensitivity in rats with IBS to better understand the pathogenesis and investigate the effect of zeta inhibitory peptide (ZIP) as a therapy for chronic visceral pain.MethodsVisceral hypersensitivity rats were produced by neonatal maternal separation (NMS). Visceral pain sensitivity was assessed by electromyographic (EMG) responses of abdominal muscles to colorectal distention (CRD). Spinal PKMζ and phosphorylated PKMζ (p-PKMζ) were detected by western blot. Varying doses of ZIP were intrathecally administered to investigate the role of spinal PKMζ in chronic visceral hypersensitivity. The open field test was used to determine if ZIP therapy causes spontaneous motor activity side effects.ResultsGraded CRD pressure significantly increased EMG responses in NMS rats compared to control rats (p < 0.05). p-PKMζ expression increased in the thoracolumbar and lumbosacral spinal cord in the IBS-like rats with notable concomitant chronic visceral pain compared to control rats (p < 0.05). EMG data revealed that intrathecal ZIP injection (1, 5, and 10 μg) dose-dependently attenuated visceral pain hypersensitivity in IBS-like rats.ConclusionsPhosphorylated PKMζ may be involved in the spinal central sensitization of chronic visceral hypersensitivity in IBS, and administration of ZIP could effectively treat chronic visceral pain with good outcomes in rat models.

Soluble Mediators Derived from Lactobacillus rhamnosus GG (LGG) Decrease Visceral Pain Hypersensitivity Induced by Early Life Stress

Maternal separation of rat pups is a robust and reliable model of early life stress that induces long‐term alterations to behavior and brain neurochemistry. These changes are particularly apparent with respect to the microbiota‐gut‐brain axis where probiotic feeding has been shown to ameliorate some of these stress‐induced alterations. It is possible that biologically relevant products of probiotic metabolism are involved in such effects, and therefore could deliver the required benefits without requiring the live organism to be present. In this study the effects of a specific preparation of soluble mediators from the probiotic Lactobacillus rhamnosus GG (LGG) were evaluated. Previously, immunomodulatory properties of this material have been demonstrated both in vitro and in vivo. Production conditions have been standardized with cultivation and downstream processing steps such as desalting, sterile filtration and lyophilization. The maternal separation protocol was conducted as described in O'Mahony et al., 2009. Rats were separated from their mothers for 3 hrs/day from postnatal day (PND) 2 to 12. Starting at weaning (PND 21), both non‐separated (NS) and maternally separated (MS) offspring were randomized into separate experimental groups and were provided drinking water with or without supplementation of LGG soluble mediators. Supplementation of the lyophilized materials was benchmarked to the number of LGG viable cells during cultivation to give a dose equivalent to a range from 1.3×108 to 4.3×108 viable LGG/animal/day throughout the study until PND 85. Visceral hypersensitivity was assessed with the colorectal distension test conducted at PND 79. There were no differences in body weight or water and food intake across groups. MS rats demonstrated visceral hypersensitivity to colorectal distension reflected by a lower pain threshold when compared to NS rats, which was ameliorated by the LGG soluble mediators (p=0.03). There were no differences in the number of observed pain behaviors between treatment groups. Interestingly, the increased pain threshold in rats that received LGG soluble mediators was not observed in animals that received unconditioned culture medium subjected to the same processing steps as the LGG soluble mediators. This indicated the presence of specific bioactives in the culture medium secreted by LGG during growth. In conclusion, administration of LGG soluble mediators in rats reversed the altered visceral pain sensitivity induced by MS. Further studies are needed to elucidate specific mechanism of actions related to gut and brain neurochemistry.Support or Funding InformationSupported by Science Foundation Ireland and Mead Johnson Nutrition.

Irritable Bowel Syndrome: A Clinical Review.

Symptoms of irritable bowel syndrome (IBS) are common in population studies including chronic abdominal pain associated with altered bowel habits. Patients often have associated gastrointestinal and somatic symptoms suggesting a possible common contributing mechanism, but the heterogeneous symptom patterns of individual patients make generalizations difficult. The pathophysiology of IBS is incompletely understood but includes disturbances of the brain-gut axis. Central mechanisms are: the psychosocial history and environment, dysfunctional brain processing of peripheral signals attributed to the intestine including the enteric nervous system, the microbiome and the innate and adaptive immune system. As a result there is visceral hypersensitivity and disturbed intestinal secretory and motor activity. Some mechanisms of visceral pain hypersensitivity may overlap with other pain syndromes including fibromyalgia (FMS). Central Sensitization (CS) would offer a way to conceptualize an integration of life experience and psychologic response into a biopsychosocial framework of pathophysiology, diagnosis and treatment of IBS. Corticotropin-releasing factor, a principle regulator in the stress and pain response may contribute to a neuroendocrine mechanism for the brain-gut interaction. The positive diagnostic approach to IBS symptoms to avoid excess testing and enhance the patient-provider therapeutic relationship requires the recognition of the "cluster" of IBS symptoms while identifying "alarm" symptoms requiring specific attention. The severity of the symptoms and other individual psychosocial factors characterize patients who seek medical care. The presence of significant psychosocial comorbidities adds to the complexity of management which often requires a multidisciplinary approach. Several treatment options exist but no single method is effective for all the symptoms of IBS. The therapeutic benefit of the well-executed physician-patient relationship is considered essential to success in managing IBS symptoms over the long term.

Antinociceptive effects of systemic tanshinone IIA on visceral and somatic persistent nociception and pain hypersensitivity in rats

Previous studies showed that tanshinone IIA (TIIA), an important lipophilic component of Danshen, has been well-established to exhibit various neuroprotective actions in the nervous system. Although we previously reported that TIIA had a significant anti-nociceptive effect in complete Freund's adjuvant (CFA)-induced pain, it is surprisingly noted that few pharmacological studies have been carried out to explore the possible analgesic action of TIIA in animals and the appropriate indications for treatment of clinical pain remain unclear. Therefore, in the present study, by using both somatic and visceral pain models, the antinociceptive and antihyperalgesic effects of TIIA were evaluated by intraperitoneal administration in rats. In the bee venom (BV) test, when compared with saline controls, systemic pre- and post-treatment with TIIA resulted in an apparent antinociception against persistent spontaneous nociception (PSN) and primary heat and mechanical hypersensitivity, while for the mirror-image heat hypersensitivity, only pre-treatment was effective. Moreover, in the formalin test, the antinociception of TIIA was significant for both phases 1 and 2 in the pretreatment groups, but only effective for phase 2 in the post-treatment group. In the acetic acid writhing test, the number of writhes was effectively blocked by both pre- and post-treatment of TIIA. Taken together, these results provide a new line of evidence showing that TIIA is also able to produce analgesia against various ‘phenotypes’ of nociception and hypersensitivity.

Tyrosine phosphorylation of the NR2B subunit of the NMDA receptor in the spinal cord contributes to chronic visceral pain in rats

The roles of spinal N-methyl-d-aspartic acid receptor 2B (NR2B) subunit in central sensitization of chronic visceral pain were investigated. A rat model with irritable bowel syndrome (IBS) was established by colorectal distention (CRD) on post-natal days 8–14. Responses of the external oblique muscle of the abdomen to CRD were measured to evaluate the sensitivity of visceral pain in rats. The sensitivity of visceral pain significantly increased in IBS-like rats. Expressions of spinal NR2B subunit and phosphorylated NR2B subunit significantly increased by 50–55% in IBS-like rats when compared with those in control rats. Ro 25-6981, a selective antagonist of NR2B subunit, has a dose-dependent anti-allodynic and anti-hyperalgesic effect without causing motor dysfunction in IBS-like rats. Furthermore, the activation mechanism of the spinal NR2B subunit in chronic visceral pain was also investigated. Spinal administration of genistein, a specific inhibitor of tyrosine kinases, also decreased the visceral pain hypersensitivity of IBS-like rats in a dose-dependent manner. In addition, the expression of phosphorylated NR2B subunit was decreased after spinal administration of Ro 25-6981 or genistein in IBS-like rats. In conclusion, tyrosine kinase activation-induced phosphorylation of NR2B subunit may play a crucial role in central sensitization of chronic visceral pain.

154. Can we predict visceral pain sensitivity? An experimental study in healthy women

Patients and healthy subjects show large inter-individual differences in visceral pain sensitivity, which may have pathophysiological relevance. However, the factors contributing to differences in pain sensitivity remain poorly understood. Thus, this study aimed to investigate psychological and biological predictors of visceral pain sensitivity in healthy subjects. Methods : In N = 59 healthy young females, psychological (i.e., state and trait anxiety, depression) and biological (i.e., gastrointestinal (GI) symptoms in daily life, serum cortisol, and serum levels of interleukin (IL)-6) were collected, followed by assessment of rectal distension pain sensitivity. To do so, rectal distension sensory and pain thresholds, and pain ratings for discrete rectal distension stimuli at pain threshold level were assessed. Results : Regression analyses revealed that lower pain thresholds were predicted by higher state anxiety and more GI symptoms in daily life (both p < .05). Increased pain ratings were predicted by lower cortisol levels ( p < .05). Additional correlation analyses showed that lower sensory thresholds were associated with GI symptoms ( p < .05). Conclusions : We observed that psychological (state anxiety) and biological (cortisol levels, subclinical GI symptoms) variables predict different aspects of visceral pain sensitivity, which is in line with results from studies in somatic pain. Our findings may help to refine our understanding of predictors and/ or risk factors for visceral pain hypersensitivity, which may contribute to the pathophysiology of visceral pain syndromes such as Irritable Bowel Syndrome.

Effect of Autonomic Modulation on Human Esophageal Pain Hypersensitivity

Introduction Patients with Functional Gastrointestinal Disorders (FGID) often display persistent and heightened pain sensitivity to experimental gut stimulation, a phenomenon known as Visceral Pain Hypersensitivity (VPH). Current management of pain in FGID involves the use of either antispasmodics or antidepressants; both are often unsatisfactory. The role of the autonomic nervous system (ANS) in modulating pain is well known; however, the effect of ANS modulation on VPH has not been studied. Methods The aim was to determine whether physiological modulation of the Autonomic Nervous System (ANS) influences the degree of oeosophageal VPH in healthy volunteers using a validated model.10 healthy volunteers (avr age 30.5 years; 8 male, 6 w-British) underwent psychological profiling for stress, anxiety and personality type. Study 1 : Pain thresholds to proximal and distal oesophageal electrical stimulation were measured. Thereafter the subjects underwent hydrochloric acid infusion (0.15 M) in the distal oesophagus for 30 min. This was followed by measurements of oesophageal pain threshold (using visual analogue scales) to electrical stimulation in the proximal, unexposed oesophagus at 30, 60 and 90 min. Study 2 was performed at an interval of 2 weeks and the protocol was identical to that of study 1 except that during the acid infusion cardiac vagal tone(CVT) was increased by deep breathing at full inspiratory capacity in 4 sec followed by forced expiratory vital capacity in 6 sec at a frequency of 0.1 Hz (6 breaths/minute, over 5 min). ANS was monitored throughout in both studies. Results The majority of volunteers were ‘agreeable extroverts’, which are protective personality factors. There was only 10% depression and 20% anxiety, showing our exclusion criteria effective. 70% of the subjects rated significant for alexithymia and showed a weak non-significant correlation with the level of sensitisation to acid (r = 0.49 p = 0.14). In study 1 in comparison to baseline, we observed a reduction in CVT during acid exposure while in study 2 the CVT increased during acid exposure, that is, (study 1 difference of -0.09 vs baseline; study 2 difference of 4.93 vs baseline) (p = 0.006). In study 2, all 10 volunteers reduced their level of oesophageal sensitisation to acid in comparison to study 1 with 50% failing to sensitise completely. Overall there was a reduction in sensitisation of 16 mA between study 1 and 2 (p = 0.004). Conclusion This preliminary study suggests that the parasympathetic nervous system has anti-hyperalgesic properties in human oesophageal VPH. This data points to a possible change in the way we treat visceral pain, highlighting likely new targets for the development of novel treatments. Further research is now required with a powered study focusing on exploring mechanism of desensitisation during deep breathing.