Effectiveness of Butorphanol in alleviating intra- and post-operative visceral pain following microwave ablation for hepatic tumor: a dual-central, randomized, controlled trial.

Many patients who underwent hepatic percutaneous microwave ablation (MWA) reported experiencing pain during the procedure. This study utilized a well-designed multicentral, randomized, and placebo-controlled format to investigate the effects of Butorphanol. Patients who underwent MWA were randomly assigned to either Butorphanol or normal saline group. The primary outcomes of the study were assessed by measuring the patients' intraoperative pain levels using a 10-point visual analog scale (VAS). Secondary outcomes included measuring postoperative pain levels at the 6-h mark (VAS) and evaluating comprehensive pain assessment outcomes. A total of 300 patients were divided between the control group (n = 100) and the experimental group (n = 200). Butorphanol showed statistically significant reductions in intraoperative pain levels compared to the placebo during surgery (5.00 ± 1.46 vs. 3.54 ± 1.67, P < 0.001). Significant differences were observed in postoperative pain levels at the 6-h mark and in the overall assessment of pain (1.39 + 1.21 vs. 0.65 + 0.81, P < 0.001). Butorphanol had a significant impact on reducing the heart rate of patients. The empirical evidence supports the effectiveness of Butorphanol in reducing the occurrence of visceral postoperative pain in patients undergoing microwave ablation for hepatic tumor. Furthermore, the study found no noticeable impact on circulatory and respiratory dynamics.

Patient-controlled intravenous administration of dexmedetomidine with nalbuphine versus sufentanil for post cesarean delivery analgesia: A retrospective observational study.

This retrospective observational study aims to investigate the patient-controlled intravenous analgesia (PCIA) of dexmedetomidine (DEX) with nalbuphine (NAL) versus sufentanil (SUF) for post-cesarean delivery management. A total of 300 women were evaluated who underwent cesarean section surgery with combined spinal-epidural anesthesia. After surgery, all patients were connected to a patient-controlled analgesia pump. The PCIA protocol was programmed with 0.11 µg/kg/h DEX in combination with 0.03 µg/kg/h SUF in Group I (n = 150) or 0.11 µg/kg/h DEX in combination with 0.03 mg/kg/h NAL in Group II (n = 150). There was no significant difference in incision pain and sedation level between the two groups within 48 h after the surgery assessed by visual analog scale (VAS) and Ramsay sedation scale, respectively. However, at 2, 6, 12, and 24 h after surgery, visceral pain at rest and at mobilization was alleviated in the Group II as compared with the Group I with lower VAS scores. Moreover, fewer adverse reactions were found in the Group II when compared with Group I, including postpartum respiratory depression, nausea/vomiting, urinary retention, and cardiovascular events. Overall, there was an increased patient satisfaction in the Group II as compared with the Group I. Based on the results of this study, it seems that adding NAL to PCIA with DEX, as compared to SUF with DEX, have an effect on reducing the intensity of visceral pain after cesarean section with less adverse reactions and higher patient satisfaction.

Effect of butorphanol on visceral pain in patients undergoing gastrointestinal endoscopy: a randomized controlled trial.

BACKGROUND: Butorphanol slightly influences the respiratory and circulatory systems, has a better effect on relieving the discomfort caused by mechanical traction, and has a low incidence of postoperative nausea and vomiting (PONV). Combined butorphanol and propofol may suppress postoperative visceral pain, which is avoidable in gastrointestinal endoscopy. Thus, we hypothesized that butorphanol could decrease the incidence of postoperative visceral pain in patients undergoing gastroscopy and colonoscopy. METHODS: This was a randomized, placebo-controlled, and double-blinded trial. Patients undergoing gastrointestinal endoscopy were randomized to intravenously receive either butorphanol (Group I) or normal saline (Group II). The primary outcome was visceral pain after the procedure 10 min after recovery. The secondary outcomes included the rate of safety outcomes and adverse events. Postoperative visceral pain was defined as a visual analog scale (VAS) score ≥ 1. RESULTS: A total of 206 patients were enrolled in the trial. Ultimately, 203 patients were randomly assigned to Group I (n = 102) or Group II (n = 101). In total, 194 patients were included in the analysis: 95 in Group I and 99 in Group II. The incidence of visceral pain at 10 min after recovery was found to be statistically lower with butorphanol than with the placebo (31.5% vs. 68.5%, respectively; RR: 2.738, 95% CI [1.409-5.319], P = 0.002), and the notable difference was in pain level or distribution of visceral pain (P = 0.006). CONCLUSIONS: The trial indicated that adding butorphanol to propofol results in a lower incidence of visceral pain after surgery without noticeable fluctuations in circulatory and respiratory functions for gastrointestinal endoscopy patients. TRIAL REGISTRATION: Clinicaltrials.gov NCT04477733 (PI: Ruquan Han; date of registration: 20/07/2020).

OCP002, a Mixed Agonist of Opioid and Cannabinoid Receptors, Produces Potent Antinociception With Minimized Side Effects.

BACKGROUND: Increasing attention has been attracted to the development of bifunctional compounds to minimize the side effects of opioid analgesics. Pharmacological studies have verified the functional interaction between opioid and cannabinoid systems in pain management, suggesting that coactivation of the opioid and cannabinoid receptors may provide synergistic analgesia with fewer adverse reactions. Herein, we developed and characterized a novel bifunctional compound containing the pharmacophores of the mu-opioid receptor agonist DALDA and the cannabinoid peptide VD-Hpα-NH2, named OCP002. METHODS: The opioid and cannabinoid agonistic activities of OCP002 were investigated in calcium mobilization and western blotting assays, respectively. Moreover, the central and peripheral antinociceptive effects of OCP002 were evaluated in mouse preclinical models of tail-flick test, carrageenan-induced inflammatory pain, and acetic acid-induced visceral pain, respectively. Furthermore, the potential opioid and cannabinoid side effects of OCP002 were systematically investigated in mice after intracerebroventricular (ICV) and subcutaneous (SC) administrations. RESULTS: OCP002 functioned as a mixed agonist toward mu-opioid, kappa-opioid, and cannabinoid CB1 receptors in vitro. ICV and SC injections of OCP002 produced dose-dependent antinociception in mouse models of nociceptive (the median effective dose [ED50] values with 95% confidence interval [CI] are 0.14 [0.12-0.15] nmol and 0.32 [0.29-0.35] µmol/kg for ICV and SC injections, respectively), inflammatory (mechanical stimulation: ED50 values [95% CI] are 0.76 [0.64-0.90] nmol and 1.23 [1.10-1.38] µmol/kg for ICV and SC injections, respectively; thermal stimulation: ED50 values [95% CI] are 0.13 [0.10-0.17] nmol and 0.23 [0.08-0.40] µmol/kg for ICV and SC injections, respectively), and visceral pain (ED50 values [95% CI] are 0.0069 [0.0050-0.0092] nmol and 1.47 [1.13-1.86] µmol/kg for ICV and SC injections, respectively) via opioid and cannabinoid receptors. Encouragingly, OCP002 cannot cross the blood-brain barrier and exerted nontolerance-forming analgesia over 6-day treatment at both supraspinal and peripheral levels. Consistent with these behavioral results, repeated OCP002 administration did not elicit microglial hypertrophy and proliferation, the typical features of opioid-induced tolerance, in the spinal cord. Furthermore, at the effective analgesic doses, SC OCP002 exhibited minimized opioid and cannabinoid side effects on motor performance, body temperature, gastric motility, physical and psychological dependence, as well as sedation in mice. CONCLUSIONS: This study demonstrates that OCP002 produces potent and nontolerance-forming antinociception in mice with reduced opioid- and cannabinoid-related side effects, which strengthen the candidacy of bifunctional drugs targeting opioid/cannabinoid receptors for translational-medical development to replace or assist the traditional opioid analgesics.

Bifunctional Peptidomimetic G Protein-Biased Mu-Opioid Receptor Agonist and Neuropeptide FF Receptor Antagonist KGFF09 Shows Efficacy in Visceral Pain without Rewarding Effects after Subcutaneous Administration in Mice.

There is still an unmet clinical need to develop new pharmaceuticals for effective and safe pain management. Current pharmacotherapy offers unsatisfactory solutions due to serious side effects related to the chronic use of opioid drugs. Prescription opioids produce analgesia through activation of the mu-opioid receptor (MOR) and are major contributors to the current opioid crisis. Multifunctional ligands possessing activity at more than one receptor represent a prominent therapeutic approach for the treatment of pain with fewer adverse effects. We recently reported on the design of a bifunctional MOR agonist/neuropeptide FF receptor (NPFFR) antagonist peptididomimetic, KGFF09 (H-Dmt-DArg-Aba-ßAla-Bpa-Phe-NH2), and its antinociceptive effects after subcutaneous (s.c.) administration in acute and persistent pain in mice with reduced propensity for unwanted side effects. In this study, we further investigated the antinociceptive properties of KGFF09 in a mouse model of visceral pain after s.c. administration and the potential for opioid-related liabilities of rewarding and sedation/locomotor dysfunction following chronic treatment. KGFF09 produced a significant dose-dependent inhibition of the writhing behavior in the acetic acid-induced writhing assay with increased potency when compared to morphine. We also demonstrated the absence of harmful effects caused by typical MOR agonists, i.e., rewarding effects (conditioned-place preference test) and sedation/locomotor impairment (open-field test), at a dose shown to be highly effective in inhibiting pain behavior. Consequently, KGFF09 displayed a favorable benefit/side effect ratio regarding these opioid-related side effects compared to conventional opioid analgesics, such as morphine, underlining the development of dual MOR agonists/NPFFR antagonists as improved treatments for various pain conditions.

Synthesis, In Vitro Profiling, and In Vivo Evaluation of Benzohomoadamantane-Based Ureas for Visceral Pain: A New Indication for Soluble Epoxide Hydrolase Inhibitors.

The soluble epoxide hydrolase (sEH) has been suggested as a pharmacological target for the treatment of several diseases, including pain-related disorders. Herein, we report further medicinal chemistry around new benzohomoadamantane-based sEH inhibitors (sEHI) in order to improve the drug metabolism and pharmacokinetics properties of a previous hit. After an extensive in vitro screening cascade, molecular modeling, and in vivo pharmacokinetics studies, two candidates were evaluated in vivo in a murine model of capsaicin-induced allodynia. The two compounds showed an anti-allodynic effect in a dose-dependent manner. Moreover, the most potent compound presented robust analgesic efficacy in the cyclophosphamide-induced murine model of cystitis, a well-established model of visceral pain. Overall, these results suggest painful bladder syndrome as a new possible indication for sEHI, opening a new range of applications for them in the visceral pain field.

Acute Visceral Pain in Rats: Vagal Nerve Block Compared to Bupivacaine Administered Intramuscularly.

BACKGROUND: Visceral and parietal peritoneum layers have different sensory innervations. Most visceral peritoneum sensory information is conveyed via the vagus nerve to the nucleus of the solitary tract (NTS). We already showed in animal models that intramuscular (i.m.) injection of local anesthetics decreases acute somatic and visceral pain and general inflammation induced by aseptic peritonitis. The goal of the study was to compare the effects of parietal block, i.m. bupivacaine, and vagotomy on spinal cord and NTS stimulation induced by a chemical peritonitis. METHODS: We induced peritonitis in rats using carrageenan and measured cellular activation in spinal cord and NTS under the following conditions, that is, a parietal nerve block with bupivacaine, a chemical right vagotomy, and i.m. microspheres loaded with bupivacaine. Proto-oncogene c-Fos (c-Fos), cluster of differentiation protein 11b (CD11b), and tumor necrosis factor alpha (TNF-α) expression in cord and NTS were studied. RESULTS: c-Fos activation in the cord was inhibited by nerve block 2 hours after peritoneal insult. Vagotomy and i.m. bupivacaine similarly inhibited c-Fos activation in NTS. Forty-eight hours after peritoneal insult, the number of cells expressing CD11b significantly increased in the cord (P = .010). The median difference in the effect of peritonitis compared to control was 30 cells (CI95, 13.5-55). TNF-α colocalized with CD11b. Vagotomy inhibited this microglial activation in the NTS, but not in the cord. This activation was inhibited by i.m. bupivacaine both in cord and in NTS. The median difference in the effect of i.m. bupivacaine added to peritonitis was 29 cells (80% increase) in the cord and 18 cells (75% increase) in the NTS. Our study underlines the role of the vagus nerve in the transmission of an acute visceral pain message and confirmed that systemic bupivacaine prevents noxious stimuli by inhibiting c-Fos and microglia activation. CONCLUSIONS: In rats receiving intraperitoneal carrageenan, i.m. bupivacaine similarly inhibited c-Fos and microglial activation both in cord and in the NTS. Vagal block inhibited activation only in the NTS. Our study underlines the role of the vagus nerve in the transmission of an acute visceral pain message and confirmed that systemic bupivacaine prevents noxious stimuli. This emphasizes the effects of systemic local anesthetics on inflammation and visceral pain.

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.

Effects of Bepridil and Pimozide, Existing Medicines Capable of Blocking T-Type Ca2+ Channels, on Visceral Pain in Mice.

T-Type Ca2+ channels (T-channels), particularly Cav3.2, are now considered as therapeutic targets for treatment of intractable pain including visceral pain. Among existing medicines, bepridil, a multi-channel blocker, used for treatment of arrhythmia and angina, and pimozide, a dopamine D2 receptor antagonist, known as a typical antipsychotic, have potent T-channel blocking activity. We thus tested whether bepridil and pimozide could suppress visceral pain in mice. Colonic and bladder pain were induced by intracolonic administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) and systemic administration of cyclophosphamide (CPA), respectively. Referred hyperalgesia was assessed by von Frey test, and colonic hypersensitivity to distension by a volume load with intracolonic water injection and spontaneous bladder pain were evaluated by observing nociceptive behaviors in conscious mice. The mice exhibited referred hyperalgesia and colonic hypersensitivity to distension on day 6 after TNBS treatment. Systemic administration of bepridil at 10-20 mg/kg or pimozide at 0.1-0.5 mg/kg strongly reduced the referred hyperalgesia on the TNBS-induced referred hyperalgesia and colonic hypersensitivity to distension. CPA treatment caused bladder pain-like nociceptive behavior and referred hyperalgesia, which were reversed by bepridil at 10-20 mg/kg or pimozide at 0.5-1 mg/kg. Our data thus suggest that bepridil and pimozide, existing medicines capable of blocking T-channels, are useful for treatment of colonic and bladder pain, and serve as seeds for the development of new medicines for visceral pain treatment.

Calcium imaging in population of dorsal root ganglion neurons unravels novel mechanisms of visceral pain sensitization and referred somatic hypersensitivity.

ABSTRACT: Mechanisms of visceral pain sensitization and referred somatic hypersensitivity remain unclear. We conducted calcium imaging in Pirt-GCaMP6s mice to gauge responses of dorsal root ganglion (DRG) neurons to visceral and somatic stimulation in vivo. Intracolonic instillation of 2,4,6-trinitrobenzene sulfonic acid (TNBS) induced colonic inflammation and increased the percentage of L6 DRG neurons that responded to colorectal distension above that of controls at day 7. Colorectal distension did not activate L4 DRG neurons. TNBS-treated mice exhibited more Evans blue extravasation than did control mice and developed mechanical hypersensitivity in low-back skin and hind paws, which are innervated by L6 and L4 DRG neurons, respectively, suggesting that colonic inflammation induced mechanical hypersensitivity in both homosegmental and heterosegmental somatic regions. Importantly, the percentage of L4 DRG neurons activated by hind paw pinch and brush stimulation and calcium responses of L6 DRG neurons to low-back brush stimulation were higher at day 7 after TNBS than those in control mice. Visceral irritation from intracolonic capsaicin instillation also increased Evans blue extravasation in hind paws and low-back skin and acutely increased the percentage of L4 DRG neurons responding to hind paw pinch and the response of L6 DRG neurons to low-back brush stimulation. These findings suggest that TNBS-induced colitis and capsaicin-induced visceral irritation may sensitize L6 DRG neurons to colorectal and somatic inputs and also increase the excitability of L4 DRG neurons that do not receive colorectal inputs. These changes may represent a potential peripheral neuronal mechanism for visceral pain sensitization and referred somatic hypersensitivity.

Pharmacologycal activity of peperina (Minthostachys verticillata) on gastrointestinal tract.

ETHNOPHARMACOLOGICAL RELEVANCE: Minthostachys verticillata (Griseb.) Epling (Lamiaceae), known as Peperina is a medicinal native plant, with a traditional use as a digestive, antispasmodic and antidiarrheic. AIM OF THE STUDY: Despite its folkloric use, no scientific evaluation of this plant related to the gastrointestinal inflammatory process has been carried out to date. The present study aims to assess the effects of M. verticillata on gastrointestinal system in experimental models. MATERIALS AND METHODS: M. verticillata (250 and 500 mg/kg) was orally tested in a colitis model induced by acetic acid. Colon weight/length ratio, oxidative stress (oxidized and reduced glutathione), histological changes using Alcian blue and hematoxylin & eosin staining and expression of IL1ß, TNFα, iNOS, COX-2 were evaluated. The effect of the extract in three additional in vivo models were studied: intestinal motility and diarrhea induced by ricin oil, and visceral pain induced by intracolonic administration of capsaicin. Finally, the activity on concentration response curves of acetylcholine, calcium chloride, potassium and serotonin were achieved in isolated rat jejunum. RESULTS: In the colitis model, M. verticillata induced a significant reduction in the colon weight/length ratio, oxidative stress and expression levels of IL-1ß, iNOS and COX-2. Also, the extract diminished the severity of microscopic tissue damage and showed protective effect on goblet cells. Intestinal motility, diarrhea, visceral pain-related behaviors and referred hyperalgesia were significantly reduced when the animals were treated with the extract. Furthermore, in isolated jejunum, M. verticillata significantly reduced the contraction induced by serotonin and acetylcholine. Likewise, the extract non-competitively inhibited the response-concentration induced by CaCl2 and inhibited both low and high K+-induced contractions. CONCLUSIONS: This is the first study to validate traditional use of M. verticillata for digestive disorders and demonstrated that its aqueous extract could represent a promising strategy in targeting the multifactorial pathophysiology of inflammatory bowel disease.

Essential role of Cav3.2 T-type calcium channels in butyrate-induced colonic pain and nociceptor hypersensitivity in mice.

Given the role of Cav3.2 isoform among T-type Ca2+ channels (T-channels) in somatic and visceral nociceptive processing, we analyzed the contribution of Cav3.2 to butyrate-induced colonic pain and nociceptor hypersensitivity in mice, to evaluate whether Cav3.2 could serve as a target for treatment of visceral pain in irritable bowel syndrome (IBS) patients. Mice of ddY strain, and wild-type and Cav3.2-knockout mice of a C57BL/6J background received intracolonic administration of butyrate twice a day for 3 days. Referred hyperalgesia in the lower abdomen was assessed by von Frey test, and colonic hypersensitivity to distension by a volume load or chemicals was evaluated by counting nociceptive behaviors. Spinal phosphorylated ERK was detected by immunohistochemistry. Cav3.2 knockdown was accomplished by intrathecal injection of antisense oligodeoxynucleotides. Butyrate treatment caused referred hyperalgesia and colonic hypersensitivity to distension in ddY mice, which was abolished by T-channel blockers and/or Cav3.2 knockdown. Butyrate also increased the number of spinal phosphorylated ERK-positive neurons following colonic distension in the anesthetized ddY mice. The butyrate-treated ddY mice also exhibited T-channel-dependent colonic hypersensitivity to intracolonic Na2S, known to enhance Cav3.2 activity, and TRPV1, TRPA1 or proteinase-activated receptor 2 (PAR2) agonists. Wild-type, but not Cav3.2-knockout, mice of a C57BL/6J background, after treated with butyrate, mimicked the T-channel-dependent referred hyperalgesia and colonic hypersensitivity in butyrate-treated ddY mice. Our study provides definitive evidence for an essential role of Cav3.2 in the butyrate-induced colonic pain and nociceptor hypersensitivity, which might serve as a target for treatment of visceral pain in IBS patients.

Enhanced spinal neuronal responses as a mechanism for increased number and size of active acupoints in visceral hyperalgesia.

Acupuncture has been used to treat a variety of illness and involves the insertion and manipulation of needles into specific points on the body (termed "acupoints"). It has been suggested that acupoints are not merely discrete, static points, but can be dynamically changed according to the pathological state of internal organs. We investigated in a rat model of mustard oil (MO)-induced visceral hyperalgesia whether the number and size of acupoints were modified according to the severity of the colonic pain, and whether the changes were associated with enhanced activity of the spinal dorsal horn. In MO-treated rats, acupoints showing neurogenic inflammation (termed "neurogenic spots" or Neuro-Sps) were found both bilaterally and unilaterally on the leg. The number and size of these acupoints increased along with increasing doses of MO. Electroacupuncture of the acupoints generated analgesic effects on MO-induced visceral hypersensitivity. The MO-treated rats showed an increase in c-Fos expression in spinal dorsal horn neurons and displayed increased evoked activity and a prolonged after-discharge in spinal wide dynamic response (WDR) neurons in response to colorectal distension. Increased number and size of neurogenic inflammatory acupoints following MO treatment were reduced by inhibiting AMPA and NMDA receptors in the spinal cord. Our findings suggest that acupoints demonstrate increased number and size along with severity of visceral pain, which may be associated with enhanced neuronal responses in spinal dorsal horn neurons.

GPER-mediated, oestrogen-dependent visceral hypersensitivity in stressed rats is associated with mast cell tryptase and histamine expression.

Visceral hypersensitivity (VH) is common in irritable bowel syndrome (IBS), and female patients are more likely to seek healthcare services for IBS-related abdominal pain. Oestrogen has been reported to mediate pain modulation via its receptor, and mast cells are known to participate in the development of visceral hypersensitivity. Our previous studies showed that the G-protein-coupled oestrogen receptor (GPER, also known as GPR30) was expressed by mast cells in human colonic tissues and was associated with IBS type and severity of visceral pain. However, whether GPER is involved in oestrogen-dependent visceral hypersensitivity via mast cell degranulation is still unknown. Rats were subjected to wrap partial restraint stress to induce visceral hypersensitivity and were ovariectomized (OVX) to eliminate the effects of oestrogen on visceral hypersensitivity. OVX rats were treated with oestrogen, an oestrogen receptor α and ß antagonist (ICI 182.780), a GPER antagonist (G15) or a GPER agonist (G1), to evaluate the effects of oestrogen via its receptor. The colorectal distention test was performed to assess visceral sensitivity. Immunofluorescence studies were performed to evaluate GPER and mast cell tryptase co-expression. Mast cell number with degranulation was detected by specific staining. Mast cell tryptase expression in rat colon was also investigated by Western blot and immunohistochemistry. Substance P and histamine expression were examined by ELISA. GPER was expressed by the majority of tryptase-positive mast cells in the colonic mucosa. Stressed rats showed increased visceral sensitivity, increased mast cell degranulation, mast cell tryptase expression, and increased colon histamine levels. Ovariectomy reduced stress-induced VH in female rats and decreased mast cell degranulation, mast cell tryptase expression, and histamine levels, whereas oestrogen replacement reversed these effects. In OVX rats, the GPER antagonist G15 counteracted the enhancing effects of oestrogen on stress-induced VH, mast cell degranulation, mast cell tryptase, and histamine expression, whereas VH was preserved after treatment with ICI 182.780. On the other hand, pretreatment with the selective GPER agonist G1 at doses between 1 and 20 µg/kg significantly increased VH, mast cell tryptase, and histamine expression in OVX-stressed rats, mimicking the effects of oestrogen. GPER plays a pivotal role in the regulation of mast cell degranulation, mast cell tryptase expression, and histamine levels and contributes to the development of colonic hypersensitivity in a female rat model of IBS.

MiR-34a affects dexmedetomidine-inhibited chronic inflammatory visceral pain by targeting to HDAC2.

BACKGROUND: Dexmedetomidine (DEX) has been used as an anesthetic for decades. The present investigation aimed to elucidate the analgesic impact of DEX on 2,4,6-Trinitrobenzenesulfonic acid (TNBS)-induced chronic inflammatory visceral pain (CIVP) in rats. METHODS: TNBS with or without DEX to Male Sprague-Dawley SD rats were randomly divided into four groups: normal, CIVP, DEX, and vehicle. Pain behaviors were assessed and the abdominal withdrawal reflex, mechanical withdrawal threshold, and thermal withdrawal latency were recorded. Quantitative polymerase chain reaction data showed increased expressions of pro-inflammatory cytokines (IL-6, IL-1ß and TNF-α) in the spinal cord tissues of rats. RESULTS: RNA microarray and quantitative polymerase chain reaction results indicated that miR-34a was downregulated by TNBS induction, but it was upregulated by DEX administration. Further studies showed that transfection of adenovirus-miR-34a inhibitor reversed the effect of DEX on the pain behaviors and spinal-cord pro-inflammatory-cytokine generation in CIVP rats. Additionally, we found that miR-34a targeted the 3'-UTR of the HDAC2 gene, as evinced by the increased HDAC2 expression in the CIVP and DEX + miR-34a inhibitor groups, and decreased HDAC2 signaling in the DEX group. Moreover, knock-down of HDAC2 restored DEX-attenuated pain behaviors and reduced pro-inflammatory cytokine production. CONCLUSIONS: DEX thus exhibited an analgesic effect on CIVP rats through the miR-34a-mediated HDAC2 pathway and suppressed visceral hypersensitivity.

Naloxone prolongs abdominal constriction writhing-like behavior in a zebrafish-based pain model.

The ability to detect noxious stimuli is essential to survival. However, pathological pain is maladaptive and severely debilitating. Endogenous and exogenous opioids modulate pain responses via opioid receptors, reducing pain sensibility. Due to the high genetic and physiological similarities to rodents and humans, the zebrafish is a valuable tool to assess pain responses and the underlying mechanisms involved in nociception. Although morphine attenuates pain-like responses of zebrafish, there are no data showing if the antagonism of opioid receptors prolongs pain duration in the absence of an exogenous opioid. Here, we investigated whether a common opioid antagonist naloxone affects the abdominal constriction writhing-like response, recently characterized as a zebrafish-based pain behavior. Animals were injected intraperitoneally with acetic acid (5.0%), naloxone (1.25 mg/kg; 2.5 mg/kg; 5.0 mg/kg) or acetic acid with naloxone to investigate the changes in their body curvature for 1 h. Acetic acid elicited a robust pain-like response in zebrafish, as assessed by aberrant abdominal body curvature, while no effects were observed following PBS injection. Although naloxone alone did not alter the frequency and duration of this behavior, it dose-dependently prolonged acetic acid-induced abdominal curvature response. Besides reinforcing the use of the abdominal writhing-like phenotype as a behavioral endpoint to measure acute pain responses in zebrafish models, our novel data suggest a putative role of endogenous opioids in modulating the recovery from pain stimulation in zebrafish.

Extrinsic Primary Afferent Neurons Link Visceral Pain to Colon Motility Through a Spinal Reflex in Mice.

BACKGROUND & AIMS: Proper colon function requires signals from extrinsic primary afferent neurons (ExPANs) located in spinal ganglia. Most ExPANs express the vanilloid receptor TRPV1, and a dense plexus of TRPV1-positive fibers is found around myenteric neurons. Capsaicin, a TRPV1 agonist, can initiate activity in myenteric neurons and produce muscle contraction. ExPANs might therefore form motility-regulating synapses onto myenteric neurons. ExPANs mediate visceral pain, and myenteric neurons mediate colon motility, so we investigated communication between ExPANs and myenteric neurons and the circuits by which ExPANs modulate colon function. METHODS: In live mice and colon tissues that express a transgene encoding the calcium indicator GCaMP, we visualized levels of activity in myenteric neurons during smooth muscle contractions induced by application of capsaicin, direct colon stimulation, stimulation of ExPANs, or stimulation of preganglionic parasympathetic neuron (PPN) axons. To localize central targets of ExPANs, we optogenetically activated TRPV1-expressing ExPANs in live mice and then quantified Fos immunoreactivity to identify activated spinal neurons. RESULTS: Focal electrical stimulation of mouse colon produced phased-locked calcium signals in myenteric neurons and produced colon contractions. Stimulation of the L6 ventral root, which contains PPN axons, also produced myenteric activation and contractions that were comparable to those of direct colon stimulation. Surprisingly, capsaicin application to the isolated L6 dorsal root ganglia, which produced robust calcium signals in neurons throughout the ganglion, did not activate myenteric neurons. Electrical activation of the ganglia, which activated even more neurons than capsaicin, did not produce myenteric activation or contractions unless the spinal cord was intact, indicating that a complete afferent-to-efferent (PPN) circuit was necessary for ExPANs to regulate myenteric neurons. In TRPV1-channel rhodopsin-2 mice, light activation of ExPANs induced a pain-like visceromotor response and expression of Fos in spinal PPN neurons. CONCLUSIONS: In mice, ExPANs regulate myenteric neuron activity and smooth muscle contraction via a parasympathetic spinal circuit, linking sensation and pain to motility.

Neonatal Maternal Deprivation Followed by Adult Stress Enhances Adrenergic Signaling to Advance Visceral Hypersensitivity.

The pathophysiology of visceral pain in patients with irritable bowel syndrome remains largely unknown. Our previous study showed that neonatal maternal deprivation (NMD) does not induce visceral hypersensitivity at the age of 6 weeks in rats. The aim of this study was to determine whether NMD followed by adult stress at the age of 6 weeks induces visceral pain in rats and to investigate the roles of adrenergic signaling in visceral pain. Here we showed that NMD rats exhibited visceral hypersensitivity 6 h and 24 h after the termination of adult multiple stressors (AMSs). The plasma level of norepinephrine was significantly increased in NMD rats after AMSs. Whole-cell patch-clamp recording showed that the excitability of dorsal root ganglion (DRG) neurons from NMD rats with AMSs was remarkably increased. The expression of ß2 adrenergic receptors at the protein and mRNA levels was markedly higher in NMD rats with AMSs than in rats with NMD alone. Inhibition of ß2 adrenergic receptors with propranolol or butoxamine enhanced the colorectal distention threshold and application of butoxamine also reversed the enhanced hypersensitivity of DRG neurons. Overall, our data demonstrate that AMS induces visceral hypersensitivity in NMD rats, in part due to enhanced NE-ß2 adrenergic signaling in DRGs.

Bile acids induce visceral hypersensitivity via mucosal mast cell-to-nociceptor signaling that involves the farnesoid X receptor/nerve growth factor/transient receptor potential vanilloid 1 axis.

Increased colonic bile acid (BA) exposure, frequent in diarrhea-predominant irritable bowel syndrome (IBS-D), can affect gut function. Nerve growth factor (NGF) is implicated in the development of visceral hypersensitivity (VH). In this study, we tested the hypothesis that BAs cause VH via mucosal mast cell (MMC)-to-nociceptor signaling, which involves the farnesoid X receptor (FXR)/NGF/transient receptor potential vanilloid (TRPV)1 axis. BAs were intracolonically administered to rats for 15 d. Visceral sensitivity to colorectal distention and colonic NGF expression were examined. BAs caused VH, an effect that involved MMC-derived NGF and was accompanied by enhanced TRPV1 expression in the dorsal root ganglia. Anti-NGF treatment and TRPV1 antagonism inhibited BA-induced VH. BAs induced NGF mRNA and protein expression and release in cultured mast cells. Colonic supernatants from patients with IBS-D with elevated colonic BA content transcriptionally induced NGF expression. In FXR-/- mice, visceral sensitivity and colonic NGF expression were unaltered after BA treatment. Pharmacological antagonism and FXR silencing suppressed BA-induced NGF expression and release in mast cells. Mitogen-activated protein kinase kinase (MKK) 3/6/p38 MAPK/NF-κB signaling was mechanistically responsible for FXR-mediated NGF expression and secretion. The findings show an MMC-dependent and FXR-mediated pronociceptive effect of BAs and identify the BA/FXR/NGF/TRPV1 axis as a key player in MMC-to-neuron communication during pain processing in IBS.-Li, W.-T., Luo, Q.-Q., Wang, B., Chen, X., Yan, X.-J., Qiu, H.-Y., Chen, S.-L. Bile acids induce visceral hypersensitivity via mucosal mast cell-to-nociceptor signaling that involves the farnesoid X receptor/nerve growth factor/transient receptor potential vanilloid 1 axis.

Oral treatment with plecanatide or dolcanatide attenuates visceral hypersensitivity via activation of guanylate cyclase-C in rat models.

AIM: To investigate the effects of plecanatide and dolcanatide on maintenance of paracellular permeability, integrity of tight junctions and on suppression of visceral hypersensitivity. METHODS: Transport of fluorescein isothiocyanate (FITC)-dextran was measured to assess permeability across cell monolayers and rat colon tissues. Effects of plecanatide and dolcanatide on the integrity of tight junctions in Caco-2 and T84 monolayers and on the expression and localization of occludin and zonula occludens-1 (ZO-1) were examined by immunofluorescence microscopy. Anti-nociceptive activity of these agonists was evaluated in trinitrobenzene sulfonic acid (TNBS)-induced inflammatory as well as in non-inflammatory partial restraint stress (PRS) rat models. Statistical significance between the treatment groups in the permeability studies were evaluated using unpaired t-tests. RESULTS: Treatment of T84 and Caco-2 monolayers with lipopolysaccharide (LPS) rapidly increased permeability, which was effectively suppressed when monolayers were also treated with plecanatide or dolcanatide. Similarly, when T84 and Caco-2 monolayers were treated with LPS, cell surface localization of tight junction proteins occludin and ZO-1 was severely disrupted. When cell monolayers were treated with LPS in the presence of plecanatide or dolcanatide, occludin and ZO-1 were localized at the cell surface of adjoining cells, similar to that observed for vehicle treated cells. Treatment of cell monolayers with plecanatide or dolcanatide without LPS did not alter permeability, integrity of tight junctions and cell surface localization of either of the tight junction proteins. In rat visceral hypersensitivity models, both agonists suppressed the TNBS-induced increase in abdominal contractions in response to colorectal distension without affecting the colonic wall elasticity, and both agonists also reduced colonic hypersensitivity in the PRS model. CONCLUSION: Our results suggest that activation of GC-C signaling might be involved in maintenance of barrier function, possibly through regulating normal localization of tight junction proteins. Consistent with these findings, plecanatide and dolcanatide showed potent anti-nociceptive activity in rat visceral hypersensitivity models. These results imply that activation of GC-C signaling may be an attractive therapeutic approach to treat functional constipation disorders and inflammatory gastrointestinal conditions.