Visceral Pain Model Research Articles

Design of a Stable Cyclic Peptide Analgesic Derived from Sunflower Seeds that Targets the κ-Opioid Receptor for the Treatment of Chronic Abdominal Pain.

The rising opioid crisis has become a worldwide societal and public health burden, resulting from the abuse of prescription opioids. Targeting the κ-opioid receptor (KOR) in the periphery has emerged as a powerful approach to develop novel pain medications without central side effects. Inspired by the traditional use of sunflower (Helianthus annuus) preparations for analgesic purposes, we developed novel stabilized KOR ligands (termed as helianorphins) by incorporating different dynorphin A sequence fragments into a cyclic sunflower peptide scaffold. As a result, helianorphin-19 selectively bound to and fully activated the KOR with nanomolar potency. Importantly, helianorphin-19 exhibited strong KOR-specific peripheral analgesic activity in a mouse model of chronic visceral pain, without inducing unwanted central effects on motor coordination/sedation. Our study provides a proof of principle that cyclic peptides from plants may be used as templates to develop potent and stable peptide analgesics applicable via enteric administration by targeting the peripheral KOR for the treatment of chronic abdominal pain.

Ulinastatin Exhibits Antinociception in Rat Models of Acute Somatic and Visceral Pain Through Inhibiting the Local and Central Inflammation.

IntroductionUlinastatin, a broad-spectrum serine protease inhibitor, has been widely used to treat various diseases clinically. However, so far, the antinociceptive effect of ulinastatin remains less studied experimentally and the underlying mechanisms of ulinastatin for pain relief remain unclear. This study aimed to find evidence of the analgesic effect of ulinastatin on acute somatic and visceral pain.MethodsThe analgesic effect of ulinastatin on acute somatic and visceral pain was evaluated by using formalin and acetic acid-induced writhing test. The analgesic mechanism of ulinastatin was verified by detecting the peripheral inflammatory cell infiltration and spinal glial activation with hematoxylin-eosin (H&E) and immunohistochemistry staining.ResultsWe found that both of intraperitoneal (i.p.) pre-administration and post-administration of ulinastatin could reduce the total number of flinching and the licking duration following intraplantar formalin injection in a dose-related manner. However, the inhibitory effect of ulinastatin existed only in the second phase (Phase 2) of formalin-induced spontaneous pain response, with no effect in the first phase (Phase 1). The formalin-induced edema and ulcer were also improved by i.p. administration of ulinastatin. Moreover, i.p. administration of ulinastatin was also able to delay the occurrence of acetic acid-induced writhing and reduced the total number of writhes dose-dependently. We further demonstrated that ulinastatin significantly decreased the local inflammatory cell infiltration in injured paw and peritoneum tissue under formalin and acetic acid test separately. The microglial and astrocytic activation in the spinal dorsal horn induced by intraplantar formalin and i.p. acetic acid injection were also dramatically inhibited by i.p. administration of ulinastatin.ConclusionOur results for the first time provided a new line of evidence showing that ulinastatin could attenuate acute somatic and visceral pain by inhibiting the peripheral and spinal inflammatory reaction.

A novel visceral pain model of uterine cervix inflammation in rat

Treatment of visceral pain originating from the uterine cervix is a substantial clinical problem. The underlying mechanisms of such visceral pain remain unclear mainly due to a lack of reliable model. This study aimed to develop and evaluate the performance of a rat model of pain induced by uterine cervix inflammation. Rats were randomized to six groups according to the solution injected into the uterine cervix: normal saline, vehicle, capsaicin (0.3 mg, 0.6 mg, 0.9 mg), capsaicin 0.9 mg + morphine (n = 15 in each group). Spontaneous behaviors after cervical injection were recorded by a computerized video system and analyzed offline. An equation for calculating a novel pain score was derived from particular behaviors, based on Pearson's correlation analysis and regression analysis. c-Fos expression in the spinal cord was detected. The pain score and c-fos expression in the spinal cord were highest in the 0.9 mg capsaicin group and lowest in the normal saline and vehicle groups (P < 0.05). Intrathecal morphine significantly decreased the pain score (P < 0.05) and c-fos expression in the spinal cord (P < 0.05). Injection of capsaicin into the uterine cervix in rats could be a practical model of inflammatory cervical pain, which can be evaluated using our novel pain score. This model will provide further insight into the mechanism underlying visceral pain originating from the uterine cervix.

Antinociceptive and Anti-Inflammatory Properties of Cannabidiol Alone and in Combination with Standardized Bioflavonoid Composition.

Symptom-alleviating therapies for osteoarthritis (OA) management are inadequate. Long-term application of first-line treatments, such as nonsteroidal anti-inflammatory drugs, is limited due to associated side effects. We believe that a combination of traditionally used botanical extracts, which have diverse active components that target multiple inflammatory pathways, may provide a safe and efficacious alternative to address the multifactorial nature of OA. Recently, cannabidiol (CBD), the major nonpsychoactive component of the hemp plant, has gained renewed global attention for its pharmacological actions. It has shown promise in reducing pain and inflammation in preclinical models of arthritis. In this study, widely employed inflammatory and noninflammatory animal pain models, such as the hot plate test, visceral pain model (writhing test), and carrageenan-induced rat paw edema model, were utilized to evaluate the antinociceptive and anti-inflammatory activity of CBD alone and in combination with standardized bioflavonoid compositions. CBD was tested at 5, 10, 20, and 40 mg/kg orally and at 5% topically. Administered alone, CBD produced dose-correlated, statistically significant pain inhibition in all the models. Enhanced performance in pain and inflammation reduction was observed when CBD was orally administered in complex with the bioflavonoid compositions. Data from this study show that for clinically meaningful efficacy against OA, CBD may have to be delivered in higher dosage or formulated with other medicinal plants with similar activities.

Analgesic and Anti-Inflammatory Effects of Perampanel in Acute and Chronic Pain Models in Mice: Interaction With the Cannabinergic System.

Pain conditions, such as neuropathic pain (NP) and persistent inflammatory pain are therapeutically difficult to manage. Previous studies have shown the involvement of glutamate receptor in pain modulation and in particular same of these showed the key role of the AMPA ionotropic glutamate receptor subtype. Antiseizure medications (ASMs) are often used to treat this symptom, however the effect of perampanel (PER), an ASM acting as selective, non-competitive inhibitor of the AMPA receptor on the management of pain has not well been investigated yet. Here we tested the potential analgesic and anti-inflammatory effects of PER, in acute and chronic pain models. PER was given orally either in acute (5 mg/kg) or repeated administration (3 mg/kg/d for 4 days). Pain response was assessed using models of nociceptive sensitivity, visceral and inflammatory pain, and mechanical allodynia and hyperalgesia induced by chronic constriction injury to the sciatic nerve. PER significantly reduced pain perception in all behavioral tests as well as CCI-induced mechanical allodynia and hyperalgesia in acute regimen (5 mg/kg). This effect was also observed after repeated treatment using the dose of 3 mg/kg/d. The antinociceptive, antiallodynic and antihyperalgesic effects of PER were attenuated when the CB1 antagonist AM251 (1 mg/kg/i.p.) was administered before PER treatment, suggesting the involvement of the cannabinergic system. Moreover, Ex vivo analyses showed that PER significantly increased CB1 receptor expression and reduced inflammatory cytokines (i.e. TNFα, IL-1β, and IL-6) in the spinal cord. In conclusion, these results extend our knowledge on PER antinociceptive and antiallodynic effects and support the involvement of cannabinergic system on its mode of action.

Importance of Non-pharmacological Approaches for Treating Irritable Bowel Syndrome: Mechanisms and Clinical Relevance.

Chronic visceral pain represents a major unmet clinical need with the severity of pain ranging from mild to so severe as to prevent individuals from participating in day-to-day activities and detrimentally affecting their quality of life. Although chronic visceral pain can be multifactorial with many different biological and psychological systems contributing to the onset and severity of symptoms, one of the major triggers for visceral pain is the exposure to emotional and physical stress. Chronic visceral pain that is worsened by stress is a hallmark feature of functional gastrointestinal disorders such as irritable bowel syndrome (IBS). Current pharmacological interventions for patients with chronic visceral pain generally lack efficacy and many are fraught with unwanted side effects. Cognitive behavioral therapy (CBT) has emerged as a psychotherapy that shows efficacy at ameliorating stress-induced chronic visceral pain; however, the molecular mechanisms underlying CBT remain incompletely understood. Preclinical studies in experimental models of stress-induced visceral pain employing environmental enrichment (EE) as an animal model surrogate for CBT are unraveling the mechanism by which environmental signals can lead to long-lasting changes in gene expression and behavior. Evidence suggests that EE signaling interacts with stress and nociceptive signaling. This review will (1) critically evaluate the behavioral and molecular changes that lead to chronic pain in IBS, (2) summarize the pharmacological and non-pharmacological approaches used to treat IBS patients, and (3) provide experimental evidence supporting the potential mechanisms by which CBT ameliorates stress-induced visceral pain.

Antinociceptive Synergy Between Metamizole and Hesperidin in a Model of Visceral Pain in Mice

Metamizole is used to relieve the visceral pain but its adverse effects limit its use. An alternative to improve its efficacy with lower doses is to combine it with a natural product as hesperidin. The aim of this study was to evaluate the antinociceptive interaction between metamizole and hesperidin in a visceral pain model using an isobolographic analysis. Antinociception was evaluated in the writhing model using acetic acid (1%) to induce writhes in mice. Metamizole (1-316mg/kg), hesperidin (3-300mg/kg), or combinations with a fixed-dose ratio of 1:1 were administered intraperitoneally 30min before the acetic acid and the number of writhes was counted for 30min. Isobolographic analysis was employed to define the nature of the compound interaction. Metamizole and hesperidin in individual administration induced dose-dependent antinociceptive effects, reached an efficacy of 84.2±5.9% and 66.3±7.4%, respectively. The ED50 values calculated from their dose-response curves were 84.5±22.7 and 108.9±17.9mg/kg, respectively. The analysis of DRC for the metamizole+hesperidin combination, in a ratio 1:1 showed a ED50 COMB value lower than the ED50 ADD estimated from the additivity line from the isobologram (46.7±6.3 vs. 96.7±11.9mg/kg, respectively). In addition, the pharmacological interaction calculated was of 0.48. These results suggest a synergistic interaction for the antinociceptive activity of metamizole+hesperidin combination. These data suggest that metamizole+hesperidin combination could be useful in treating visceral pain as it can interact synergistically using low dose of both drugs with the possibility of reducing the risk of adverse effects.

The Role of a Dopaminergic Component in the Analgesic Effect of the Low-Affinity NMDA Receptor Antagonist Hemantane

The role of dopaminergic transmission in the mechanism of analgesic action of the low-affinity NMDAreceptor antagonist hemantane [N-(2-adamantyl)hexamethyleneimine hydrochloride] was demonstrated experimentally. A single i.p. injection of hemantane at a dose of 20 mg/kg has the ability to inhibit dopamine reuptake and exhibits an analgesic effect in the somatic thermal pain model (tail-flick test) and visceral pain model (acetic-acid-induced writhing test) in ICR mice. The dopamine D1 receptor antagonist R(+)-SCH-23390 at a dose of 0.005 mg/kg and dopamine D2 receptor antagonist sulpiride at a dose of 5 mg/kg administered by a single i.p. injection 30 min before hemantane injection prevented manifestation of the antinociceptive activity of the NMDA receptor antagonist in the used methods, which was more pronounced for the spinal reflex (tail-flick test).

Intrathecal administration of neuronostatin induces an antinociceptive effect in a mouse visceral pain model

Neuronostatin (NST) is a peptide encoded by the somatostatin gene that serves important physiological functions in diverse tissues. Previous studies have shown that intracerebroventricular administration of NST induces antinociceptive effects and hyperalgesic effects as determined by the tail immersion assay and formalin test, respectively. In the present study, we aimed to evaluate the effects of intrathecal (i.t.) injection of NST on nociception in a model of visceral pain, and determine possible mechanisms of action in mice. NST (1, 3, 6, or 12 nmol) was administered to mice, leading to a dose‐dependent antinociceptive effect as determined by the acetic acid‐induced writhing test in mice. NST (1 nmol) also enhanced the antinociceptive effect of morphine (2.5 and 5 μg/kg) in the spine. Naloxone and β‐funaltrexamine hydrochloride significantly antagonized the antinociceptive effect of NST. The expression of G‐protein‐coupled receptor 107 (GPR107) protein and the phosphorylation of PKA at Thr197 were increased after i.t. administration of NST, suggesting that the μ‐opioid receptor and GPR107/PKA signaling pathway are involved in the analgesic response. In conclusion, i.t. injection of NST may potentially be used as a new approach in the mediation of visceral pain.

Antinociception and less gastric injury with the dexketoprofen-tapentadol combination in mice.

The purpose of this study was to evaluate the antinociceptive interaction between dexketoprofen and tapentadol in three different dose ratios, as well as the ulcerogenic activity of this combination. Dose-response curves were carried out for dexketoprofen, tapentadol, and dexketoprofen-tapentadol combinations in the acetic acid-induced writhing test in mice. On the other hand, the gastric damage of all treatments was assessed after the surgical extraction of the stomachs. Intraperitoneal administration of dexketoprofen and tapentadol induced a dose-dependent antinociceptive effect, reaching a maximal effect of about 58% and 99%, respectively. Isobolographic analysis and the interaction index showed that the three proportions produced an analgesic potentiation (synergistic interaction). Interestingly, the 1:1 and 1:3 ratios of the drugs combination produced minor gastric injury in comparison with the 3:1 proportion. Our data suggest that all proportions of the dexketoprofen-tapentadol combination produced a synergistic interaction in the acetic acid-induced visceral pain model in mice with a low incidence of gastric injury.

Роль дофаминергического компонента в механизме анальгетического действия низкоаффинного блокатора NMDA рецептора гимантана

В проведённом экспериментальном исследовании выявлена роль дофаминергического компонента в механизме анальгетического действия низкоаффинного блокатора NMDA рецептора гимантана (N-(2-адамантил)гексаметиленимина гидрохлорида). Гимантан, обладающий способностью ингибировать обратный захват дофамина, при однократном внутрибрюшинном введении в дозе 20 мг/кг проявляет анальгетический эффект на моделях соматической термической (тест отдёргивания хвоста от теплового излучения) и висцеральной (тест «Уксусные корчи») боли у мышей ICR. Блокатор D1-дофаминергического рецептора R(+)-SCH-23390 в дозе 0,005 мг/кг и блокатор D2-дофаминергического рецептора сульпирид в дозе 5 мг/кг при однократном внутрибрюшинном введении за 30 мин до инъекции гимантана предотвращают проявление антиноцицептивной активности изучаемого блокатора NMDA рецептора в используемых методиках, что более ярко проявляется при оценке его влияния на спинальный флексорный рефлекс.

Possible implications of animal models for the assessment of visceral pain.

Acute pain, provoked generally after the activation of peripheral nociceptors, is an adaptive sensory function that alerts the individual to avoid noxious stimuli. However, uncontrolled acute pain has a maladaptive role in sensory activity leading to development of a chronic pain state which persists even after the damage is resolved, or in some cases, in the absence of an initial local acute injury. Huge numbers of people suffer from visceral pain at least once during their life span, leading to substantial health care costs. Although studies reporting on the mechanism of visceral pain are accumulating, it is still not precisely understood. Therefore, this review aims to elucidate the mechanism of visceral pain through an evaluation of different animal models and their application to develop novel therapeutic approaches for treating visceral pain. To assess the nociceptive responses in viscera, several visceral pain models such as inflammatory, traction, stress and genetic models utilizing different methods of measurement have been devised. Among them, the inflammatory and traction models are widely used for studying the visceral pain mechanism of different disease conditions and post‐operative surgery in humans and animals. A hapten, 2,4,6‐trinitrobenzene sulfonic acid (TNBS), has been extensively used as an inflammatory agent to induce visceral pain. The traction model seems to cause a strong pain stimulation and autonomic reaction and could thus be the most appropriate model for studying the underlying visceral pain mechanism and for probing the therapeutic efficacies of various anesthetic and analgesics for the treatment of visceral pain and hyperalgesia.

Deepening the Mechanisms of Visceral Pain Persistence: An Evaluation of the Gut-Spinal Cord Relationship.

The management of visceral pain is a major clinical problem in patients affected by gastrointestinal disorders. The poor knowledge about pain chronicization mechanisms prompted us to study the functional and morphological alterations of the gut and nervous system in the animal model of persistent visceral pain caused by 2,4-dinitrobenzenesulfonic acid (DNBS). This agent, injected intrarectally, induced a colonic inflammation peaking on day 3 and remitting progressively from day 7. In concomitance with bowel inflammation, the animals developed visceral hypersensitivity, which persisted after colitis remission for up to three months. On day 14, the administration of pain-relieving drugs (injected intraperitoneally and intrathecally) revealed a mixed nociceptive, inflammatory and neuropathic pain originating from both the peripheral and central nervous system. At this time point, the colonic histological analysis highlighted a partial restitution of the tunica mucosa, transmural collagen deposition, infiltration of mast cells and eosinophils, and upregulation of substance P (SP)-positive nerve fibers, which were surrounded by eosinophils and MHC-II-positive macrophages. A significant activation of microglia and astrocytes was observed in the dorsal and ventral horns of spinal cord. These results suggest that the persistence of visceral pain induced by colitis results from maladaptive plasticity of the enteric, peripheral and central nervous systems.

Receptors involved in dexketoprofen analgesia in murine visceral pain

Various animal models, especially rodents, are used to study pain, due to the difficulty of studying it in humans. Many drugs that produce analgesia have been studied and there is evidence among which NSAIDs deserve to be highlighted. Dexketoprofen (DEX) provides a broad antinociceptive profile in different types of pain; therefore, this study was designed to evaluate the profile of antinociceptive potency in mice. Analgesic activity was evaluated using the acetic acid abdominal constriction test (writhing test), a chemical model of visceral pain. Dose-response curves for i.p. DEX administration (1, 3, 10, 30 and 100 mg/kg), using at least six mice in each of at least five doses, was obtained before and 30 min after pre-treatment with different pharmacological agents. Pretreatment of the mice with opioid receptor antagonists was not effective; however, the serotonin receptor antagonist and nitric oxide synthase inhibitor produce a significant increase in DEX-induced antinociception. The data from the present study shows that DEX produces antinociception in the chemical twisting test of mice, which is explained with difficulty by the simple inhibition of COX. This effect appears to be mediated by other mechanisms in which the contribution of the NO and 5-HT pathways has an important effect on DEXinduced antinociception.

Spinal administration of the multi-functional opioid/neuropeptide FF agonist BN-9 produced potent antinociception without development of tolerance and opioid-induced hyperalgesia

Chronic opioids treatment is impeded by the development of analgesic tolerance and opioid-induced hyperalgesia. Recent studies have shown that multi-functional opioid compounds produce analgesic activities with limited side effects. We developed a novel multi-functional peptide targeting opioid and neuropeptide FF receptors named BN-9, which produced potent and non-tolerance forming antinociceptive effect after supraspinal and systemic administrations. In the present study, the analgesic properties and potential side effects of intrathecal BN-9 were investigated in a range of preclinical rodent models. In complete Freund's adjuvant-induced inflammatory pain model, intrathecal BN-9 dose-dependently produced analgesic effect via opioid receptors, and the spinal antinociceptive effect was augmented by the neuropeptide FF receptor antagonist RF9. In contrast, in plantar incision-induced postoperative pain model, BN-9 exhibited potent anti-allodynic effect via opioid receptors and, at least partially, neuropeptide FF receptors. In mouse models of acetic acid-induced visceral pain and formalin pain, BN-9-induced spinal antinociception was mainly mediated by opioid receptors, independent of neuropeptide FF receptors. Furthermore, at the spinal level, chronic treatments with BN-9 did not lead to analgesic tolerance and cross-tolerance to morphine. Moreover, opioid-induced hyperalgesia was observed after repeated administration of morphine, but not BN-9. Taken together, our present study suggests that intrathecal BN-9 produces potent and non-tolerance forming antinociception, and does not cause opioid-induced hyperalgesia. Thus, BN-9 might serve as a promising lead compound in the development of multi-functional opioid analgesics with minimized side effects.

Sex Differences Linking Pain-Related Fear and Interoceptive Hypervigilance: Attentional Biases to Conditioned Threat and Safety Signals in a Visceral Pain Model.

Although the broad role of fear and hypervigilance in conditions of the gut-brain axis like irritable bowel syndrome is supported by converging evidence, the underlying mechanisms remain incompletely understood. Even in healthy individuals, it remains unclear how pain-related fear may contribute to pain-related attentional biases for acute visceral pain. Building on our classical fear conditioning work in a clinically relevant model of visceral pain, we herein elucidated pain-related attentional biases shaped by associative learning in healthy women and men, aiming to elucidate possible sex differences and the role of psychological traits. To this end, we compared the impact of differentially conditioned pain-predictive cues on attentional biases in healthy women and men. Sixty-four volunteers accomplished a visual dot-probe task and subsequently underwent pain-related fear conditioning where one visual cue (CS+) was contingently paired with a painful rectal distention (US) while another cue remained unpaired (CS−). During the following test phase, the dot-probe task was repeated to investigate changes in attentional biases in response to differentially valenced cues. While pain-related learning was comparable between groups, men revealed more pronounced attentional engagement with the CS+ and CS− whereas women demonstrated stronger difficulties to disengage from the CS+ when presented with a neutral cue. However, when both CS+ and CS− were presented together, women revealed stronger difficulties to disengage from the CS−. Regression analyses revealed an interaction of sex, with negative affect predicting stronger avoidance of the CS+ and stronger difficulties to disengage attention from the CS− in men. These results provide first evidence that pain-related fear conditioning may induce attentional biases differentially in healthy women and men. Hence, sex differences may play a role in attentional mechanisms underlying hypervigilance, and may be modulated by psychological vulnerability factors relevant to chronic visceral pain.

The Ventrolateral Periaqueductal Gray Contributes to Depressive-Like Behaviors in Recovery of Inflammatory Bowel Disease Rat Model.

BackgroundPatients with inflammatory bowel disease (IBD) experience depression, even in the remission phase of IBD symptoms. Although mapping depression-associated brain regions through the gut-brain axis can contribute to understanding the process, the mechanisms remain unclear. Our previous results support the idea that glutamatergic transmission in the ventrolateral periaqueductal gray (vlPAG) mediates stress-induced depression-like behaviors. Thus, we hypothesize that the vlPAG plays a role in regulating depression during remission of IBD.MethodsWe used dextran sulfate sodium (DSS)-induced visceral pain model to evoke depression-like behaviors, assessed by tail suspension test (TST) and sucrose preference test (SPT), and electrophysiological recordings from vlPAG.ResultsSymptoms of animals modeling IBD were relieved by replacing DSS solution with normal drinking water, but their depression-like behaviors sustained. Moreover, the impairment of glutamatergic neurotransmission in vlPAG was sustained as well. Pharmacologically, microinfusion of the glutamate receptor 1 (GluR1) antagonist NASPM into vlPAG mimicked the depression-like behaviors. Furthermore, intra-vlPAG application of AMPA and AMPA receptor-mediated antidepressant (2R,6R)-hydroxynorketamine [(2R,6R)-HNK] reversed the DSS-induced depression-like behaviors in the remission phase of visceral abnormalities.ConclusionOur results suggest that vlPAG glutamatergic transmission mediates depression-like behaviors during remission of DSS-induced visceral pain, suggesting that vlPAG mapping to the gut-brain axis contributes to depression during remission of IBD.

Dissection of Pelvic Autonomic Ganglia and Associated Nerves in Male and Female Rats.

The bilateral major pelvic ganglia (MPG; synonym, pelvic ganglia) are the primary source of postganglionic sympathetic and parasympathetic neurons innervating pelvic organs of rodents; the functionally equivalent structure in humans is the inferior hypogastric plexus. The major pelvic ganglia also provide the route by which lumbar and sacral sensory axons reach the pelvic organs. These complex, mixed ganglia can prove challenging to identify and dissect for further experimental study of normal autonomic mechanisms or to establish preclinical models of disease, injury or visceral pain. Here we describe a protocol to access and visualize these ganglia and their associated nerve tracts. We provide this protocol with schematics for both male and female rats, as the ganglion size and landmarks for identification differ between sexes. The protocol describes removal of the ganglion for in vitro studies, but this method can be integrated into a surgical recovery protocol for experimental interventions (e.g., nerve crush, nerve resection) or for mapping neuronal circuits (e.g., by microinjection of neural tracers). We also demonstrate the primary structures of the ganglion and its associated nerves immediately following dissection and following immunohistochemical staining.

Pharmacological evaluation of a novel corticotropin‐releasing factor 1 receptor antagonist T‐3047928 in stress‐induced animal models in a comparison with alosetron

The major symptoms of irritable bowel syndrome (IBS) are changes in bowel habits and abdominal pain. Psychological stress is the major pathophysiological components of IBS. Corticotropin-releasing factor (CRF) is a well-known integrator in response to psychological stress. In this study, a novel CRF1 receptor antagonist T-3047928 was evaluated in stress-induced IBS models of rats to explore its potency for IBS. Plasma adrenocorticotropic hormone (ACTH) levels after intravenous oCRH challenge were measured as a pharmacodynamic marker. Efficacies of oral T-3047928 were compared with oral alosetron, a 5-HT3 antagonist, on conditioning fear stress (CFS)-induced defecation, restraint stress (RS)-induced acute visceral pain, specific alteration of rhythm in temperature (SART) stress-induced chronic visceral pain, and normal defecation. T-3047928 (1-10mg/kg, p.o.) demonstrated a dose-dependent inhibition on oCRH-induced ACTH secretion. In disease models, T-3047928 suppressed fecal pellet output induced by CFS and improved both acute and chronic visceral hypersensitivity induced by RS and SART stress, respectively. Alosetron was also efficacious in stress-induced defecation and visceral pain models at 1 and 10mg/kg, respectively. Alosetron, however, also suppressed normal defecation at lower those. On the other hand, T-3047928 did not change normal defecation even at higher dose than those in disease models. T-3047928 is an orally active CRF1 antagonist that demonstrated potent inhibitory effects in stress-associated IBS models with no effect on normal defecation. Therefore, it is suggested that T-3047928 may have a potency as a novel option for IBS-D therapy with minimal constipation risk.

Decreased Glutamatergic Synaptic Strength in the Periaqueductal Gray Contributes to Maintenance of Visceral Pain in Male Rats with Experimental Pancreatitis

Visceral pain originating from chronic inflammation of the pancreas is often intractable and difficult to manage clinically. However, the pathogenesis of the central nervous system underlying visceral pain is still poorly understood. The aim of the present study was to investigate the role of the midbrain ventrolateral periaqueductal gray (vlPAG) in a rat model of chronic visceral pain induced by pancreatitis. In the present study, we used a well-established rat model of chronic pancreatitis induced by tail vein injection of dibutyltin dichloride (DBTC). To assess the DBTC-induced visceral pain, we examined the abdominal withdrawal by von Frey filament test. We further studied the synaptic transmission in the vlPAG by whole-cell patch-clamp electrophysiological recordings. Rats receiving DBTC injection exhibited a significantly increased withdrawal frequency to mechanical stimulation of the abdomen compared to rats injected with vehicle. Interestingly, compared to rats injected with vehicle, we found that neurons dissected from DBTC-treated rats exhibited a significantly decreased synaptic strength, which was revealed by a diminishedα-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/N-methyl-d-aspartic acid (AMPA/NMDA) ratio in the vlPAG. Moreover, our results further demonstrated that neurons obtained from DBTC-treated rats displayed a higher paired-pulse ratio, as well as less frequent and smaller amplitudes of miniature excitatory postsynaptic currents in the vlPAG compared to rats injected with vehicle. Furthermore, intra-vlPAG microinjection of AMPA alleviated DBTC-induced abdominal hypersensitivity. Taken together, our findings suggest that diminished glutamatergic synaptic strength via both presynaptic and postsynaptic mechanisms in the midbrain vlPAG is associated with DBTC-induced abdominal hypersensitivity. In addition, activation of AMPA receptors in the vlPAG alleviates DBTC-induced abdominal hypersensitivity.