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

ABSTRACT: 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.

Gut enterochromaffin cells drive visceral pain and anxiety.

Gastrointestinal (GI) discomfort is a hallmark of most gut disorders and represents an important component of chronic visceral pain1. For the growing population afflicted by irritable bowel syndrome, GI hypersensitivity and pain persist long after tissue injury has resolved2. Irritable bowel syndrome also exhibits a strong sex bias, afflicting women three times more than men1. Here, we focus on enterochromaffin (EC) cells, which are rare excitable, serotonergic neuroendocrine cells in the gut epithelium3-5. EC cells detect and transduce noxious stimuli to nearby mucosal nerve endings3,6 but involvement of this signalling pathway in visceral pain and attendant sex differences has not been assessed. By enhancing or suppressing EC cell function in vivo, we show that these cells are sufficient to elicit hypersensitivity to gut distension and necessary for the sensitizing actions of isovalerate, a bacterial short-chain fatty acid associated with GI inflammation7,8. Remarkably, prolonged EC cell activation produced persistent visceral hypersensitivity, even in the absence of an instigating inflammatory episode. Furthermore, perturbing EC cell activity promoted anxiety-like behaviours which normalized after blockade of serotonergic signalling. Sex differences were noted across a range of paradigms, indicating that the EC cell-mucosal afferent circuit is tonically engaged in females. Our findings validate a critical role for EC cell-mucosal afferent signalling in acute and persistent GI pain, in addition to highlighting genetic models for studying visceral hypersensitivity and the sex bias of gut pain.

Paragastric Autonomic Neural Blockade to Prevent Early Visceral Pain and Associated Symptoms After Laparoscopic Sleeve Gastrectomy: a Randomized Clinical Trial.

BACKGROUND: Visceral pain (VP) following laparoscopic sleeve gastrectomy remains a substantial problem. VP is associated with autonomic symptoms, especially nausea and vomiting, and is unresponsive to traditional pain management algorithms aimed at alleviating somatic (incisional) pain. The present study was performed to evaluate the safety and effectiveness of laparoscopic paragastric autonomic neural blockade (PG-ANB) in managing the symptoms associated with VP following sleeve gastrectomy. STUDY DESIGN: This prospective, double-blinded, randomized clinical trial involved patients undergoing laparoscopic sleeve gastrectomy at two high-volume institutions. The patients were randomized to laparoscopic transversus abdominis plane block with or without PG-ANB. The primary outcome was patient-reported pain scores assessed at 1, 8, and 24 h postoperatively. The secondary outcome measures were analgesic requirements, nausea, vomiting, hiccups, and hemodynamic changes immediately after PG-ANB and postoperatively. RESULTS: In total, 145 patients (block group, n = 72; control group, n = 73) were included in the study. The heart rate and mean arterial pressure significantly decreased 10 min after PG-ANB. The visual analog scale score for pain was significantly lower in the PG-ANB than in the control group at 1 h postoperatively (p < 0.001) and 8 h postoperatively (p < 0.001). Vomiting, nausea, sialorrhea, and hiccups were significantly less prevalent in the PG-ANB group. Patients in the PG-ANB group received fewer cumulative doses of analgesics at 1 h postoperatively (p = 0.003) and 8 h postoperatively (p < 0.001). No differences between the groups were detected at 24 h (p = 0.298). No complications related to PG-ANB occurred. CONCLUSION: PG-ANB safely and effectively reduces early VP, associated autonomic symptoms, and analgesic requirements after laparoscopic sleeve gastrectomy.

Lactococcus lactis NCDO2118 exerts visceral antinociceptive properties in rat via GABA production in the gastro-intestinal tract.

Gut disorders associated to irritable bowel syndrome (IBS) are combined with anxiety and depression. Evidence suggests that microbially produced neuroactive molecules, like γ-aminobutyric acid (GABA), can modulate the gut-brain axis. Two natural strains of Lactococcus lactis and one mutant were characterized in vitro for their GABA production and tested in vivo in rat by oral gavage for their antinociceptive properties. L. lactis NCDO2118 significantly reduced visceral hypersensitivity induced by stress due to its glutamate decarboxylase (GAD) activity. L. lactis NCDO2727 with similar genes for GABA metabolism but no detectable GAD activity had no in vivo effect, as well as the NCDO2118 ΔgadB mutant. The antinociceptive effect observed for the NCDO2118 strain was mediated by the production of GABA in the gastro-intestinal tract and blocked by GABAB receptor antagonist. Only minor changes in the faecal microbiota composition were observed after the L. lactis NCDO2118 treatment. These findings reveal the crucial role of the microbial GAD activity of L. lactis NCDO2118 to deliver GABA into the gastro-intestinal tract for exerting antinociceptive properties in vivo and open avenues for this GRAS (Generally Recognized As safe) bacterium in the management of visceral pain and anxious profile of IBS patients.

[Eosinophilic duodenitis associated to food allergy debuting as acute visceral pain in an adult with vitiligo: a case report]. / Duodenitis eosinofílica asociada a alergia alimentaria debutando como dolor visceral agudo en un adulto con vitíligo: reporte de un caso.

BACKGROUND: Eosinophilic duodenitis has a prevalence of 5.1 to 8.2 per 100000 persons. The underlying molecular mechanisms are unknown, but hypersensitivity (seasonal and food allergies, asthma, eczema) response plays a major role in its pathogenesis, allergic predisposition can be found up-to 25-35% of cases. The diagnosis includes clinical manifestation, imaging findings and histological evidence of eosinophilic infiltration >20 eosinophils per high-power field. This is a clinical case report. a 25-years old man with vitiligo consult to emergency department referring dyspepsia symptoms, vomiting and abdominal pain of maximal intensity, in the medical exam upper abdominal pain was found, blood laboratories were unremarkable except a high net eosinophil-count >2000 cells/ul, abdominal ultrasound were normal, upper endoscopy revealed duodenitis with rigid and thickened folds, colonoscopy show hemorrhoids grade I. Coproscopy exam was negative for parasites, total IgE, IgA and IgG were in normal range, a positive IgG to Toxoplasma gondii was reported, autoimmunity panel was negative. In the following 4 days the abdominal pain and eosinophils count increase, a new abdomin-pelvic tomography was done showing thickened duodenum with a new endoscopy showing marked edema in duodenum with severe biliary reflux with biopsies describing an atrophic chronic duodenitis. Allergy tests -skin prick and patch tests- were done resulting positive to cereals (rye, soy, barley), Manihot esculenta, green banana, tomato, cow milk, orange and pineapple. A restrictive diet and protons pump inhibitor was indicated, ambulatory control at 45 days after show symptoms resolution with a normal blood eosinophils count. Here is reported a case of eosinophilic duodenitis related to food allergy in a young man with vitiligo debuting with an unusual clinical presentation of acute visceral pain and biliary reflux which resolved with elimination diet and pantoprazole without use of corticoids, with both, IgE and non-IgE mechanisms playing important roles explaining food sensitization.

Downregulation of GRK6 in arcuate nucleus promotes chronic visceral hypersensitivity via NF-κB upregulation in adult rats with neonatal maternal deprivation.

AIMS: The arcuate nucleus is a vital brain region for coursing of pain command. G protein-coupled kinase 6 (GRK6) accommodates signaling through G protein-coupled receptors. Studies have demonstrated that GRK6 is involved in inflammatory pain and neuropathic pain. The present study was designed to explore the role and the underlying mechanism of GRK6 in arcuate nucleus of chronic visceral pain. METHODS: Chronic visceral pain of rats was induced by neonatal maternal deprivation and evaluated by monitoring the threshold of colorectal distension. Western blotting, immunofluorescence, real-time quantitative polymerase chain reaction techniques, and Nissl staining were employed to determine the expression and mutual effect of GRK6 with nuclear factor κB (NF-κB). RESULTS: Expression of GRK6 in arcuate nucleus was significantly reduced in neonatal maternal deprivation rats when compared with control rats. GRK6 was mainly expressed in arcuate nucleus neurons, but not in astrocytes, and a little in microglial cells. Neonatal maternal deprivation reduced the percentage of GRK6-positive neurons of arcuate nucleus. Overexpression of GRK6 by Lentiviral injection into arcuate nucleus reversed chronic visceral pain in neonatal maternal deprivation rats. Furthermore, the expression of NF-κB in arcuate nucleus was markedly upregulated in neonatal maternal deprivation rats. NF-κB selective inhibitor pyrrolidine dithiocarbamate suppressed chronic visceral pain in neonatal maternal deprivation rats. GRK6 and NF-κB were expressed in the arcuate nucleus neurons. Importantly, overexpression of GRK6 reversed NF-κB expression at the protein level. In contrast, injection of pyrrolidine dithiocarbamate once daily for seven consecutive days did not alter GRK6 expression in arcuate nucleus of neonatal maternal deprivation rats. CONCLUSIONS: Present data suggest that GRK6 might be a pivotal molecule participated in the central mechanisms of chronic visceral pain, which might be mediated by inhibiting NF-κB signal pathway. Overexpression of GRK6 possibly represents a potential strategy for therapy of chronic visceral pain.

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

BACKGROUND: Stress 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. METHODS: In 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 RESULTS: Stress 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 INFERENCES: The data indicate many similarities but some differences in mechanisms contributing to comorbid pain conditions compared to transient stress-induced pain.

Environmental enrichment prevents chronic stress-induced brain-gut axis dysfunction through a GR-mediated mechanism in the central nucleus of the amygdala.

BACKGROUND: Cognitive behavioral therapy (CBT) improves quality of life of patients with irritable bowel syndrome (IBS), a disorder characterized by chronic visceral pain and abnormal bowel habits. Whether CBT can actually improve visceral pain in IBS patients is still unknown. The aim of this study is to evaluate whether environment enrichment (EE), the animal analog of CBT, can prevent stress-induced viscero-somatic hypersensitivity through changes in glucocorticoid receptor (GR) signaling within the central nucleus of the amygdala (CeA). METHODS: Rats were housed in either standard housing (SH) or EE for 7 days before and during daily water avoidance stress (WAS) exposure (1-h/d for 7 days). In the first cohort, visceral and somatic sensitivity were assessed via visceromotor response to colorectal distention and von Frey Anesthesiometer 24 hous and 21 days after WAS. In another cohort, the CeA was isolated for GR mRNA quantification. KEY RESULTS: Environment enrichment for 7 days before and during the 7 days of WAS persistently attenuated visceral and somatic hypersensitivity when compared to rats placed in SH. Environment enrichment exposure also prevented the WAS-induced decrease in GR expression in the CeA. CONCLUSION & INFERENCES: Pre-exposure to short-term EE prevents the stress-induced downregulation of GR, and inhibits visceral and somatic hypersensitivity induced by chronic stress. These results suggest that a positive environment can ameliorate stress-induced pathology and provide a non-pharmacological therapeutic option for disorders such as IBS.

Co-occurrence of pain syndromes.

Many pain conditions in patients tend to co-occur, influencing the clinical expressions of each other in various ways. This paper summarizes the main concurrent pain conditions by analyzing the major interactions observed. In particular, co-occurrence will be examined in: visceral pain (especially ischemic heart disease, irritable bowel syndrome, dysmenorrhea/endometriosis and urinary pain), fibromyalgia, musculoskeletal pain and headache. Two concurrent visceral pains from internal organs sharing at least part of their central sensory projection can give rise to viscero-visceral hyperalgesia, i.e., enhancement of typical pain symptoms from both districts. Visceral pain, headache and musculoskeletal pains (myofascial pain from trigger points, joint pain) can enhance pain and hyperalgesia from fibromyalgia. Myofascial pain from trigger points can perpetuate pain symptoms from visceral pain conditions and trigger migraine attacks when located in the referred pain area from an internal organ or in cervico-facial areas, respectively. The pathophysiology of these pain associations is complex and probably multifactorial; among the possible processes underlying the mutual influence of symptoms recorded in the associations is modulation of central sensitization phenomena by nociceptive inputs from one or the other condition. A strong message in these pain syndrome co-occurrence is that effective treatment of one of the conditions can also improve symptoms from the other, thus suggesting a systematic and thorough evaluation of the pain patient for a global effective management of his/her suffering.

Dehydroepiandrosterone sulfate improves visceral sensation and gut barrier in a rat model of irritable bowel syndrome.

Stress-induced altered visceral sensation and impaired gut barrier play an important role in the pathophysiology of irritable bowel syndrome (IBS). These responses were demonstrated to be peripheral corticotropin-releasing factor (CRF) dependent and also mediated via proinflammatory cytokine in animal IBS model. Dehydroepiandrosterone sulfate (DHEA-S) is known to have anti-inflammatory properties by suppressing proinflammatory cytokine release. We hypothesized that DHEA-S improves stress-induced visceral changes and is beneficial for IBS treatment. We explored the effects of DHEA-S on lipopolysaccharide (LPS)- or repeated water avoidance stress (WAS)-induced visceral allodynia and increased colonic permeability (rat IBS models). The threshold of visceromotor response, i.e. abdominal muscle contractions induced by colonic balloon distention was electrophysiologically measured. Colonic permeability was estimated in vivo by quantifying the absorbed Evans blue in colonic tissue. DHEA-S abolished visceral allodynia and colonic hyperpermeability induced by LPS in a dose-dependent manner. It also blocked repeated WAS- or peripheral injection of CRF-induced visceral changes. These effects by DHEA-S in LPS model were reversed by bicuculline, a γ-aminobutyric acid (GABA)A receptor antagonist, NG-nitro-L-arginine methyl ester, a nitric oxide (NO) synthesis inhibitor, naloxone, an opioid receptor antagonist, or sulpiride, a dopamine D2 receptor antagonist. However, domperidone, a peripheral dopamine D2 receptor antagonist did not modify the effects. Peripheral injection of astressin2-B, a selective CRF receptor subtype 2 (CRF2) antagonist also reversed these effects. In conclusion, DHEA-S blocked stress-induced visceral changes via GABAA, NO, opioid, central dopamine D2 and peripheral CRF2 signaling. DHEA-S may be useful for IBS treating.

MiRNA-29a modulates visceral hyperalgesia in irritable bowel syndrome by targeting HTR7.

Some patients with irritable bowel syndrome (IBS) have visceral hypersensitivity, which contributes to their abdominal pain. miRNA-29 was detected to be significantly upregulated in colonic tissues of patients with IBS. However, it is unknown whether miRNA-29a is involved in the visceral hypersensitivity pathogenesis of IBS. This study aimed to investigate whether miRNA-29a participates in visceral hypersensitivity in IBS. We investigated miRNA-29a in intestinal biopsies collected during endoscopy of patients with IBS (n = 10) and healthy volunteers (control) (n = 10). In addition, a water avoidance stress (WAS)-induced visceral hypersensitivity IBS mouse model was established. The abdominal withdrawal reflex (AWR) scores of mice in response to colorectal distention were used to assess visceral sensitivity. Reverse transcription quantitative-polymerase chain reaction (RT-qPCR) was used to measure miRNA-29a levels. Immunofluorescence, RT-qPCR and western blot were used to measure 5-HT7 receptor (HTR7) levels. Bioinformatic analysis and luciferase reporter assays were used to detect the direct relationship between miRNA-29a and HTR7. Finally, alterations in the levels of HTR7 and miRNA-29a were measured in the human intestinal epithelial cell line NCM460 after transfection with miRNA-29a inhibitor or mimic. Intestinal tissues from patients with IBS and WAS-induced IBS mice had increased levels of miRNA-29a, but reduced levels of HTR7. MiRNA-29a knockout resulted in overexpression of HTR7 and attenuated visceral hyperalgesia in WAS-induced IBS mice. HTR7 was a direct target of miRNA-29a. Based on analyses of intestinal tissue samples from patients with IBS and WAS-induced miRNA-29a-/- mice, miRNA-29a plays a role in the visceral hyperalgesia pathogenesis of IBS, probably through regulating HTR7 expression.

The IASP classification of chronic pain for ICD-11: chronic secondary visceral pain.

Chronic visceral pain is a frequent and disabling condition. Despite high prevalence and impact, chronic visceral pain is not represented in ICD-10 in a systematic manner. Chronic secondary visceral pain is chronic pain secondary to an underlying condition originating from internal organs of the head or neck region or of the thoracic, abdominal, or pelvic regions. It can be caused by persistent inflammation, by vascular mechanisms or by mechanical factors. The pain intensity is not necessarily fully correlated with the disease process, and the chronic visceral pain may persist beyond successful treatment of the underlying cause. This article describes how a new classification of chronic secondary visceral pain is intended to facilitate the diagnostic process and to enable the collection of accurate epidemiological data. Furthermore, it is hoped that the new classification will improve the tailoring of patient-centered pain treatment of chronic secondary visceral pain and stimulate research. Chronic secondary visceral pain should be distinguished from chronic primary visceral pain states that are considered diseases in their own right.

Interventional Pain Management and Female Pelvic Pain: Considerations for Diagnosis and Treatment.

Chronic pelvic pain (CPP) is a recurring and/or constant pain of at least six months duration that has resulted in either functional or psychological disability that can require interventional treatments. Chronic pelvic pain can be visceral, somatic, neuropathic, or a combination. Patients with CPP often suffer from concurrent bowel or bladder dysfunction, sexual dysfunction, depression, and anxiety. The complexity of chronic pelvic pain can be challenging to treat, which can lead to frustration for both patients and their physicians. Treatment should involve a comprehensive and multi-modal approach involving psychosocial support, counseling, physical therapy, medication management, and interventional procedures. This manuscript will focus both on the etiologies and the interventional treatment options for chronic pelvic pain.

Extracellular signal-regulated kinase activation in the spinal cord contributes to visceral hypersensitivity induced by craniofacial injury followed by stress.

BACKGROUND: We previously developed an animal model to examine mechanisms that underlie the emergence of visceral hypersensitivity modeling pain characteristics of temporomandibular disorder (TMD) patients with comorbid irritable bowel syndrome (IBS). In ovariectomized (OVx) rats with estradiol (E2) replacement, visceral hypersensitivity developed subsequent to masseter muscle inflammation followed by repeated forced swim (FS) stress. The purpose of this study was to investigate whether activation of extracellular signal-regulated kinase (ERK) in the spinal cord contributes to visceral hypersensitivity in this overlapping pain model. METHODS: In OVx with E2 replacement rats masseter muscle inflammation was followed by 3 day FS (comorbid condition). Depression-like behaviors were assessed by sucrose preference and in the elevated plus maze, and visceral sensitivity was measured by the visceromotor response (VMR) to colorectal distention. The protein level of ERK1/2 and phosphorylated ERK1/2 (p-ERK1/2) in the L6-S2 dorsal spinal cord was analyzed by western blot. KEY RESULTS: FS stress decreased sucrose consumption in E2 replaced rats in sucrose preference test. The expression of p-ERK1/2 in the L6-S2 dorsal spinal cord increased significantly in E2 with comorbid rats. Intrathecal injection of mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor PD98059 blocked the visceral hypersensitivity induced by masseter muscle inflammation combined with FS stress. CONCLUSIONS & INFERENCES: These data indicate that ERK1/2 activation contributes to the visceral hypersensitivity evoked by craniofacial inflammation pain combined with stress. The results may provide a new therapeutic avenue for alleviating overlapping pain conditions.

Antinociceptive Effect of Ghrelin in a Rat Model of Irritable Bowel Syndrome Involves TRPV1/Opioid Systems.

BACKGROUND/AIMS: Irritable bowel syndrome (IBS), defined as recurrent abdominal pain and changes in bowel habits, seriously affects quality of life and ability to work. Ghrelin is a brain-gut hormone, which has been reported to show antinociceptive effects in peripheral pain. We investigated the effect of ghrelin on visceral hypersensitivity and pain in a rat model of IBS. METHODS: Maternal deprivation (MD) was used to provide a stress-induced model of IBS in Wistar rats. Colorectal distension (CRD) was used to detect visceral sensitivity, which was evaluated by abdominal withdrawal reflex (AWR) scores. Rats that were confirmed to have visceral hypersensitivity after MD were injected with ghrelin (10 µg/kg) subcutaneously twice a week from weeks 7 to 8. [D-Lys3]-GHRP-6 (100 nmol/L) and naloxone (100 nmol/L) were administered subcutaneously to block growth hormone secretagogue receptor 1α (GHS-R1α) and opioid receptors, respectively. Expression of transient receptor potential vanilloid type 1 (TRPV1) and µ and κ opioid receptors (MOR and KOR) in colon, dorsal root ganglion (DRG) and cerebral cortex tissues were detected by western blotting, quantitative real-time polymerase chain reaction (qRT-PCR), immunohistochemical analyses and immunofluorescence. RESULTS: Ghrelin treatment increased expression of opioid receptors and inhibited expression of TRPV1 in colon, dorsal root ganglion (DRG) and cerebral cortex. The antinociceptive effect of ghrelin in the rat model of IBS was partly blocked by both the ghrelin antagonist [D-Lys3]-GHRP-6 and the opioid receptor antagonist naloxone. CONCLUSION: The results indicate that ghrelin exerted an antinociceptive effect, which was mediated via TRPV1/opioid systems, in IBS-induced visceral hypersensitivity. Ghrelin might potentially be used as a new treatment for IBS.

Visceral pain as a triggering factor for fibromyalgia symptoms in comorbid patients.

Fibromyalgia syndrome (FMS) is a central sensitization syndrome; however, peripheral pain sources potentially exacerbate its symptoms of chronic diffuse musculoskeletal pain and hyperalgesia. This prospective study evaluated visceral pain as a possible triggering factor for FMS pain and hyperalgesia in comorbid patients. Women with (1) FMS + irritable bowel syndrome (IBS); (2) FMS + primary dysmenorrhea (Dys); (3) FMS + Dys secondary to endometriosis (Endo); (4) FMS + colon diverticulosis (Div) were compared with FMS-only women, for fibromyalgia pain (number and intensity of episodes and analgesic consumption) over comparable periods and for somatic hyperalgesia (electrical and pressure pain thresholds) in painful (tender points) and control areas (trapezius, deltoid, quadriceps muscles, and overlying subcutis and skin). In comorbid subgroups, FMS symptoms were also reassessed after treatment of the visceral condition or no treatment. All comorbid groups vs FMS-only had significantly higher FMS pain (number/intensity of episodes and analgesic consumption) and hyperalgesia in deep somatic tissues (subcutis and muscle) at all sites (0.05 < P < 0.0001). Visceral pain (number of IBS days, painful menstrual cycles, and abdominal pain episodes from diverticulitis) correlated directly with all parameters of FMS pain and inversely with muscle pain thresholds at all sites (0.03 < P < 0.0001). Fibromyalgia syndrome pain and hyperalgesia in all tissues and all sites significantly decreased in patients after visceral comorbidity treatment (dietary for 6 months [IBS], hormonal for 6 months [dysmenorrhea], laser [endometriosis], and surgery [diverticulosis]) (0.05 < P < 0.0001) vs no change in untreated patients. Visceral pain enhances FMS symptoms, probably augmenting the level of central sensitization typical of the syndrome. Systematic assessment and treatment of visceral pain comorbidities should be a part of FMS management strategy.

Neonatal bladder inflammation induces long-term visceral pain and altered responses of spinal neurons in adult rats.

Painful events early in life have been shown to increase the incidence of interstitial cystitis/painful bladder syndrome in adulthood. However, the intrinsic mechanism is not well studied. We previously reported that neonatal bladder inflammation causes chronic visceral hypersensitivity along with molecular disruption of spinal GABAergic system in rats. The present study investigates whether these molecular changes affect the integrative function and responses of bladder-sensitive primary afferent and spinal neurons. Neonatal bladder inflammation was induced by intravesicular injection of zymosan during postnatal (P) days 14-16. In adulthood (P60), the viscero-motor response (VMR) to visceral stimuli was significantly inhibited by intrathecal (i.t) HZ166 (GABAAα-2 agonist) only in neonatally saline-treated, but not in neonatally zymosan-treated rats. HZ166 significantly inhibited the responses of bladder-responsive lumbosacral (LS) spinal neurons to urinary bladder distension (UBD) and slow infusion (SI) in neonatally saline-treated rats. Similar results were also observed in naïve adult rats where HZ166 produced significant inhibition of bladder-responsive spinal neurons. However, HZ166 did not inhibit responses of UBD-responsive spinal neurons from neonatally zymosan-treated rats. The drug did not attenuate the responses of UBD-sensitive pelvic nerve afferent (PNA) fibers to UBD and SI in either group of rats tested. Immunohistochemical studies showed a significantly lower level of GABAAα-2 receptor expression in the LS spinal cord of neonatally zymosan-treated rats compared to saline-treated rats. These findings indicate that neonatal bladder inflammation leads to functional and molecular alteration of spinal GABAAα-2 receptor subtypes, which may result in chronic visceral hyperalgesia in adulthood.

Impairment of decision making associated with disruption of phase-locking in the anterior cingulate cortex in viscerally hypersensitive rats.

Visceral hypersensitivity (VH) is a key factor of irritable bowel syndrome (IBS). Previous studies have identified an enhanced response of anterior cingulate cortex (ACC) to colorectal distension in VH rats, which can be observed up to 7weeks following colonic anaphylaxis, independent of colonic inflammation. The induction of VH produces a change in the ability to induce subsequent synaptic plasticity at the ACC circuitry. In clinical practice, a positive link between IBS and cognitive impairments has been noted for years, but no animal model has been reported. Decision-making is a valuable model for monitoring higher-order cognitive functions in animals, which depends on the integrated function of several sub-regions of the ACC and amygdala. Using rat gambling task (RGT) in the present study, we observed an impairment of decision-making behavior in VH rats. Electrophysiological study showed a reduction of long-term potentiation in the basolateral amygdala (BLA)-ACC synapses in VH rats. Multiple-electrode array recordings of local field potential (LFP) in both BLA and ACC were also performed in freely behaving rats. Spike-field coherence (SFC) analysis revealed chronic visceral pain led to disruption of ACC spike timing and BLA local theta oscillation. Finally, cross-correlation analysis revealed that VH was associated with suppressed synchronization of theta oscillation between the BLA and ACC, indicating reduced neuronal communications between these two regions under the VH state. The present results demonstrate that functional disturbances in BLA-ACC neural circuitry may be relevant causes for the deficits in decision-making in chronic pain state.

Changes in mast cell infiltration: a possible mechanism in detrusor overactivity induced by visceral hypersensitivity.

OBJECTIVE: To establish the detrusor overactivity (DO) model induced by visceral hypersensitivity (VH) and investigate the relationship between mast cell (MC) infiltration and DO. MATERIALS AND METHODS: Sixty rats are divided into 4 groups randomly: Group 1:Baseline group; Group 2: DO group; Group 3: CON group; Group 4: VH group. The colorectal distension (CRD) and abdominal withdral reflex (AWR) scores are performed to evaluate VH. The cystometric investigation and histological test of MC infiltration are assessed. RESULTS: The threshold pressure of CRD in the VH group is significantly lower than that in the CON group (P<0.001). At the distension pressure ≥20 mmHg, the AWR scores of the VH group are significantly higher than those of the CON group (10 mmHg: P=0.33; 20 mmHg: P=0.028; 40 mmHg: P<0.001; 60 mmHg: P<0.001; 80 mmHg: P<0.001). DO model is successfully established in the VH group (DO rate=100%). Compared with the CON group, the numbers of MC infiltration are significantly increased in the VH group, including submucosa of bladder (P<0.001), mucosa lamina propria/mesentery of small intestine (P<0.001), and mucosa lamina propria/mesentery of large intestine (P<0.001). Furthermore, more MC activation as well as degranulation are observed in the VH group. CONCLUSIONS: It is indicated that DO model can be established in the VH rats. The MC infiltration may play an important role in DO induced by VH, and may be helpful to understand the mechanisms of DO in VH patients.