Emerging evidence indicates that gut dysbiosis is involved in the pathogenesis of visceral hypersensitivity (VH). However, how gut microbiota contributes to the development of VH is unknown. Here, we sought to examine the signal transduction pathways from gut to dorsal root ganglion (DRG) responsible for this. Therefore, abdominal withdrawal reflex (AWR) scores, fecal output, fecal water content, and total gastrointestinal transit time (TGITT) were assessed in Con rats, VH rats, rats treated with NaB, and VH rats treated with VSL#3. Fecal microbiota and its metabolite (short-chain fatty acids, SCFAs), mast cell degranulation in colon, lincRNA-01028, miR-143, and protease kinase C (PKC) and TRPV1 expression in DRGs were further detected. VH rats showed an increased fecal water content, a shortened TGITT, an increased abundance of Clostridium sensu stricto 1 and increased butyrate in fecal samples, an increased mast cell degranulation, an increased expression of lincRNA-01028, PKC, and TRPV1, and a decreased expression of miR-143 in DRGs compared with control rats, which could be restored by the application of probiotic VSL#3. The above-mentioned detection in rats treated with butyrate was similar to that of VH rats. We further confirm whether butyrate sensitized DRG neurons by a lincRNA-01028, miR-143, and PKC-dependent mechanism via mast cell in vitro. In co-cultures, MCs treated with butyrate elicited a higher TRPV1 current, a higher expression of lincRNA-01028, PKC, and a lower expression of miR-143 in DRG neurons, which could be inhibited by a lincRNA-01028 inhibitor. These findings indicate that butyrate promotes visceral hypersensitivity via mast cell-derived DRG neuron lincRNA-01028-PKC-TRPV1 pathway.IMPORTANCEIrritable bowel syndrome (IBS), characterized by visceral hypersensitivity, is a common gastrointestinal dysfunction syndrome. Although the gut microbiota plays a role in the pathogenesis and treatment of irritable bowel syndrome (IBS), the possible underlying mechanisms are unclear. Therefore, it is of critical importance to determine the signal transduction pathways from gut to DRG responsible for this in vitro and in vivo assay. This study demonstrated that butyrate sensitized TRPV1 in DRG neurons via mast cells in vivo and in vitro by a lincRNA-01028, miR-143, and PKC-dependent mechanism. VH rats similarly showed an increased abundance of Clostridium sensu stricto 1, an increased fecal butyrate, an increased mast cell degranulation, and increased expression of TRPV1 compared with control rats, which could be restored by the application of VSL#3. In conclusion, butyrate produced by the altered intestinal microbiota is associated with increased VH.

Functional gastrointestinal disorders (FGIDs), chronic disorders characterized by either abdominal pain, altered intestinal motility, or their combination, have a worldwide prevalence of more than 40% and impose a high socioeconomic burden with a significant decline in quality of life. Recently, FGIDs have been reclassified as disorders of gut-brain interaction (DGBI), reflecting the key role of the gut-brain bidirectional communication in these disorders and their impact on psychological comorbidities. Although, during the past decades, the field of DGBIs has advanced significantly, the molecular mechanisms underlying DGBIs pathogenesis and pathophysiology, and the role of the gut microbiome in these processes are not fully understood. This review aims to discuss the latest body of literature on the complex microbiota-gut-brain interactions and their implications in the pathogenesis of DGBIs. A better understanding of the existing communication pathways between the gut microbiome and the brain holds promise in developing effective therapeutic interventions for DGBIs.

Although multiple purinergic receptors mediate the analgesic effects of acupuncture, it remains unclear whether there is mutual interaction between purinergic receptors to jointly mediate the electroacupuncture inhibition of peripheral sensitization in visceral pain. Visceral hypersensitivity was induced by intracolonic 2,4,6-trinitrobenzene sulfonic acid (TNBS) in rat. The antinociception effect of electroacupuncture on visceral pain was evaluated by morphology, behaviors, neuroelectrophysiology and molecular biology techniques. After labeling the colon-related primary sensory neurons with neural retrograde tracer and employing neuropharmacology, neuroelectrophysiology, and molecular biotechnology, the mechanisms of P2X7R, P2Y1R, and P2X3R in colon-related dorsal root ganglion (DRG) neurons alleviating visceral hypersensitivity of irritable bowel syndrome (IBS) by electroacupuncture at Zusanli and Sanyinjiao acupoints.were elucidated from the perspective of peripheral sensitization. Electroacupuncture significantly inhibited TNBS-induced colonic hypersensitivity in rats with IBS, and Satellite Glial Cells (SGCs) in DRG were found to be involved in electroacupuncture-mediated regulation of the electrophysiological properties of neurons. P2X7R was found to play a pain-inducing role in IBS visceral hypersensitivity by affecting P2X3R, and electroacupuncture exerted an analgesic effect by inhibiting P2X7R activation. P2Y1R was found to play an analgesic role in the process of visceral pain, mediating electroacupuncture to relieve visceral hypersensitivity. P2Y1R relieved visceral pain by inhibiting P2X3R in neurons associated with nociception, with P2X7R identified as upstream of P2Y1R up-regulation by electroacupuncture. Our study suggests that the P2X7R → P2Y1R → P2X3R inhibitory pathway in DRG mediates the inhibition of peripheral sensitization by electroacupuncture in rats with IBS visceral hypersensitivity.

(1) Background: Irritable bowel syndrome (IBS) is a common disease in the gastrointestinal (GI) tract. Atractylodes macrocephala Koidz (AMK) is known as one of the traditional medicines that shows a good efficacy in the GI tract. (2) Methods: We investigated the effect of AMK in a network pharmacology and zymosan-induced IBS animal model. In addition, we performed electrophysiological experiments to confirm the regulatory mechanisms related to IBS. (3) Results: Various characteristics of AMK were investigated using TCMSP data and various analysis systems. AMK restored the macroscopic changes and weight to normal. Colonic mucosa and inflammatory factors were reduced. These effects were similar to those of amitriptyline and sulfasalazine. In addition, transient receptor potential (TRP) V1, voltage-gated Na+ (NaV) 1.5, and NaV1.7 channels were inhibited. (4) Conclusion: These results suggest that AMK may be a promising therapeutic candidate for IBS management through the regulation of ion channels.

Irritable bowel syndrome (IBS), which is characterized by chronic abdominal pain, has a high global prevalence. The anterior cingulate cortex (ACC), which is a pivotal region involved in pain processing, should be further investigated regarding its role in the regulation of visceral sensitivity and mental disorders. A C57BL/6J mouse model for IBS was established using chronic acute combining stress (CACS). IBS-like symptoms were assessed using behavioral tests, intestinal motility measurements, and abdominal withdrawal reflex scores. Fluoro-Gold retrograde tracing and immunohistochemistry techniques were employed to investigate the projection of ACC gamma-aminobutyric acid-producing (GABAergic) neurons to the lateral hypothalamus area (LHA). Chemogenetic approaches enabled the selective activation or inhibition of the ACC-LHA GABAergic pathway. Enzyme-linked immunosorbent assay (ELISA) and western blot analyses were conducted to determine the expression of histamine, 5-hydroxytryptamine (5-HT), and transient receptor potential vanilloid 4 (TRPV4). Our findings suggest that CACS induced IBS-like symptoms in mice. The GABA type A receptors (GABAAR) within LHA played a regulatory role in modulating IBS-like symptoms. The chemogenetic activation of ACC-LHA GABAergic neurons elicited anxiety-like behaviors, intestinal dysfunction, and visceral hypersensitivity in normal mice; however, these effects were effectively reversed by the administration of the GABAAR antagonist Bicuculline. Conversely, the chemogenetic inhibition of ACC-LHA GABAergic neurons alleviated anxiety-like behaviors, intestinal dysfunction, and visceral hypersensitivity in the mouse model for IBS. These results highlight the crucial involvement of the ACC-LHA GABAergic pathway in modulating anxiety-like behaviors, intestinal motility alterations, and visceral hypersensitivity, suggesting a potential therapeutic strategy for alleviating IBS-like symptoms.

Nowadays, the pharmacological management of visceral hypersensitivity associated with colitis is ineffective. In this context, targeting purinergic P2X4 receptor (P2X4R), which can modulate visceral pain transmission, could represent a promising therapeutic strategy. Herein, we tested the pain-relieving effect of two novel and selective P2X4R antagonists (NC-2600 and NP-1815-PX) in a murine model of DNBS-induced colitis and investigated the mechanisms underlying their effect. Tested drugs and dexamethasone (DEX) were administered orally, two days after colitis induction. Treatment with tested drugs and DEX improved tissue inflammatory parameters (body weight, spleen weight, macroscopic damage, TNF and IL-1β levels) in DNBS-rats. In addition, NC-2600 and NP-1815-PX attenuated visceral pain better than DEX and prevented the reduction of occludin expression. In in vitro studies, treatment of CaCo2 cells with supernatant from THP-1 cells, previously treated with LPS plus ATP, reduced the expression of tight junctions protein. By contrast, CaCo2 cells treated with supernatant from THP-1 cells, previously incubated with tested drugs, counteracted the reduction of tight junctions due to the inhibition of P2X4R/NLRP3/IL-1β axis. In conclusion, these results suggest that the direct and selective inhibition of P2X4R represents a viable approach for the management of visceral pain associated with colitis via NLRP3/IL-1β axis inhibition.

Chronic abdominal pain in the absence of ongoing disease is the hallmark of disorders of gut-brain interaction (DGBIs), including irritable bowel syndrome (IBS). While the etiology of DGBIs remains poorly understood, there is evidence that both genetic and environmental factors play a role. In this study, we report the identification and validation of arginine-vasopressin receptor 1A (Avpr1a) as a novel candidate gene for visceral hypersensitivity (VH), a primary peripheral mechanism underlying abdominal pain in DGBI/IBS. Comparing 2 C57BL/6 (BL/6) substrains (C57BL/6NTac and C57BL/6J) revealed differential susceptibility to the development of chronic VH following intrarectal zymosan instillation, a validated preclinical model for postinflammatory IBS. Using whole-genome sequencing, we identified a single-nucleotide polymorphism differentiating the 2 strains in the 5\' intergenic region upstream of Avpr1a, encoding the protein Avpr1a. We used behavioral, histological, and molecular approaches to identify distal colon-specific gene expression and neuronal hyperresponsiveness covarying with Avpr1a genotype and VH susceptibility. While the 2 BL/6 substrains did not differ across other gastrointestinal phenotypes (eg, fecal water retention), VH-susceptible BL/6NTac mice had higher colonic Avpr1a mRNA and protein expression. These results parallel findings that patients\' colonic Avpr1a mRNA expression corresponded to higher pain ratings. Moreover, neurons of the enteric nervous system were hyperresponsive to the Avpr1a agonist arginine-vasopressin, suggesting a role for enteric neurons in the pathology underlying VH. Taken together, these findings implicate differential regulation of Avpr1a as a novel mechanism of VH susceptibility as well as a potential therapeutic target specific to VH. PERSPECTIVE: This article presents evidence of Avpr1a as a novel candidate gene for VH in a mouse model of IBS. Avpr1a genotype and/or tissue-specific expression represents a potential biomarker for chronic abdominal pain susceptibility.

Functional abdominal pain is a disorder in which central and peripheral sensitization processes converge, leading to hypersensitivity and allodynia. Differential diagnosis is made with organic digestive, renal, gynecological, endocrine, or neurological diseases. Treatment should be individualized for each patient. In cases of debilitating pain, therapy combining drugs with different mechanisms of action can be initiated, while in less severe cases, therapy with a progressive introduction of drugs based on clinical response is advised. The first line includes general lifestyle advice and antispasmodic substances, like peppermint oil, anticholinergic/antimuscarinic, and calcium channels antagonists. In the second line of treatment, neuromodulating agents are added. Finally, when these measures fail, third-line treatments such as gabapentine and atypical antipsychotics are considered. Psychological interventions should be considered if specialized therapists are available to manage these disorders.

Visceral and somatic hypersensitivity is a common cause of functional dyspepsia. Marine bioactive components have been revealed to possess numerous valuable abilities. However, as a kind of polysaccharide extracted from brown algae, the study focused on the biological properties of laminarin is still limited, especially in gastrointestinal disorders. In our study, indicators associated with visceral sensational function and gastrointestinal microecology were determined to investigate the modulatory effects of laminarin on functional dyspepsia induced by iodoacetamide. Mice with visceral hypersensitivity were orally administrated with laminarin (50 and 100 mg per kg bw) for fourteen days. The results indicated that laminarin partly alleviated the dysfunction by regulating corticosterone secretion, the expression of 5HT3 receptors at both protein and mRNA levels, and mechanical transduction through the PIEZO2-EPAC1 axis. Furthermore, laminarin administration moderated the imbalanced gut microbial profile, including modulating the abundance of Bacteroidetes and Firmicutes. Our findings revealed that laminarin may restore the overexpression of 5HT3 receptors, the abnormal mechanical transduction, and impaired gut microecology. In conclusion, we provide evidence to support the utilization of laminarin as the ingredient of complementary and alternative medicine of regulating visceral and somatic hypersensitivity.

BACKGROUND: Serotonin receptor 2B (5-HT2B receptor) plays a critical role in many chronic pain conditions. The possible involvement of the 5-HT2B receptor in the altered gut sensation of irritable bowel syndrome with diarrhea (IBS-D) was investigated in the present study.
OBJECTIVE: To investigate the possible involvement of 5-HT2B receptor in the altered gut sensation in rat model and patients with IBS-D.
METHODS: Rectosigmoid biopsies were collected from 18 patients with IBS-D and 10 patients with irritable bowel syndrome with constipation who fulfilled the Rome IV criteria and 15 healthy controls. The expression level of the 5-HT2B receptor in colon tissue was measured using an enzyme-linked immunosorbent assay and correlated with abdominal pain scores. The IBS-D rat model was induced by intracolonic instillation of acetic acid and wrap restraint. Alterations in visceral sensitivity and 5-HT2B receptor and transient receptor potential vanilloid type 1 (TRPV1) expression were examined following 5-HT2B receptor antagonist administration. Changes in visceral sensitivity after administration of the TRPV1 antagonist were recorded.
RESULTS: Here, we observed greater expression of the 5-HT2B receptor in the colonic mucosa of patients with IBS-D than in that of controls, which was correlated with abdominal pain scores. Intracolonic instillation of acetic acid and wrap restraint induced obvious chronic visceral hypersensitivity and increased fecal weight and fecal water content. Exogenous 5-HT2B receptor agonist administration increased visceral hypersensitivity, which was alleviated by successive administration of a TRPV1 antagonist. IBS-D rats receiving the 5-HT2B receptor antagonist exhibited inhibited visceral hyperalgesia.Moreover, the percentage of 5-HT2B receptor-immunoreactive (IR) cells surrounded by TRPV1-positive cells (5-HT2B receptor I+) and total 5-HT2B receptor IR cells (5-HT2B receptor IT) in IBS-D rats was significantly reduced by the administration of a 5-HT2B receptor antagonist.
CONCLUSIONS: Our finding that increased expression of the 5-HT2B receptor contributes to visceral hyperalgesia by inducing TRPV1 expression in IBS-D patients provides important insights into the potential mechanisms underlying IBS-D-associated visceral hyperalgesia.