5-HT3 receptors promote colonic inflammation via activation of substance P/neurokinin-1 receptors in dextran sulphate sodium-induced murine colitis

Lycopene alleviates BCG-induced depressive phenotypes in mice by disrupting 5-HT3 receptor - IDO1 interplay in the brain

The 5-HT3 receptor and indoleamine 2,3-dioxygenase 1 (IDO1) enzyme play a crucial role in the pathogenesis of depression as their activation reduces serotonin contents in the brain. Since molecular docking analysis revealed lycopene as a potent 5-HT3 receptor antagonist and IDO1 inhibitor, we hypothesized that lycopene might disrupt the interplay between the 5-HT3 receptor and IDO1 to mitigate depression. In mice, the depression-like phenotypes were induced by inoculating Bacillus Calmette-Guerin (BCG). Lycopene (intraperitoneal; i.p.) was administered alone or in combination with 5-HT3 receptor antagonist ondansetron (i.p.) or IDO1 inhibitor minocycline (i.p.), and the behavioral screening was performed by the sucrose preference test, open field test, tail suspension test, and splash test which are based on the different principles. Further, the brains were subjected to the biochemical analysis of serotonin and its precursor tryptophan by the HPLC. The results showed depression-like behavior in BCG-inoculated mice, which was reversed by lycopene administration. Moreover, prior treatment with ondansetron or minocycline potentiated the antidepressant action of lycopene. Minocycline pretreatment also enhanced the antidepressant effect of ondansetron indicating the regulation of IDO1 activity by 5-HT3 receptor-triggered signaling. Biochemical analysis of brain samples revealed a drastic reduction in the levels of tryptophan and serotonin in depressed animals, which were restored following treatment with lycopene and its combination with ondansetron or minocycline. Taken together, the data from molecular docking, behavioral experiments, and biochemical estimation suggest that lycopene might block the 5-HT3 receptor and consequently inhibit the activity of IDO1 to ameliorate BCG-induced depression in mice.

Novel 5-HT7 receptor antagonists modulate intestinal immune responses and reduce severity of colitis

Inflammatory bowel disease (IBD) encompasses several debilitating chronic gastrointestinal (GI) inflammatory disorders, including Crohn's disease and ulcerative colitis. In both conditions, mucosal inflammation is a key clinical presentation associated with altered serotonin (5-hydroxytryptamine or 5-HT) signaling. This altered 5-HT signaling is also found across various animal models of colitis. Of the 14 known receptor subtypes, 5-HT receptor type 7 (5-HT7) is one of the most recently discovered. We previously reported that blocking 5-HT signaling with either a selective 5-HT7 receptor antagonist (SB-269970) or genetic ablation alleviated intestinal inflammation in murine experimental models of colitis. Here, we developed novel antagonists, namely, MC-170073 and MC-230078, which target 5-HT7 receptors with high selectivity. We also investigated the in vivo efficacy of these antagonists in experimental colitis by using dextran sulfate sodium (DSS) and the transfer of CD4+CD45RBhigh T cells to induce intestinal inflammation. Inhibition of 5-HT7 receptor signaling with the antagonists, MC-170073 and MC-230078, ameliorated intestinal inflammation in both acute and chronic colitis models, which was accompanied by lower histopathological damage and diminished levels of proinflammatory cytokines compared with vehicle-treated controls. Together, the data reveal that the pharmacological inhibition of 5-HT7 receptors by these selective antagonists ameliorates the severity of colitis across various experimental models and may, in the future, serve as a potential treatment option for patients with IBD. In addition, these findings support that 5-HT7 is a viable therapeutic target for IBD.NEW & NOTEWORTHY This study demonstrates that the novel highly selective 5-HT7 receptor antagonists, MC-170073 and MC-230078, significantly alleviated the severity of colitis across models of experimental colitis. These findings suggest that inhibition of 5-HT7 receptor signaling by these new antagonists may serve as an alternative mode of treatment to diminish symptomology in those with inflammatory bowel disease.

Neutrophil extracellular trap induction through peptidylarginine deiminase 4 activity is involved in 2,4,6-trinitrobenzenesulfonic acid-induced colitis

Neutrophil extracellular traps (NETs) are induced in the innate immune response against infectious agents and are also implicated in the pathogenesis of various cancers and autoimmune diseases. Peptidylarginine deiminase 4 (PAD4), an enzyme that converts arginine to citrulline, is also involved in NET formation. In this study, we investigated the pathogenic effect of PAD4 on NETs in inflammatory bowel disease using a trinitrobenzene sulfonic acid (TNBS)-induced murine colitis model. PAD4-deficient (PAD4KO) mice were generated by CRISPR-Cas9-mediated genomic editing. NETs were triggered in peritoneal neutrophils obtained from wild-type mice by A23187 (a calcium ionophore), but these responses were completely abolished in the PAD4KO mice. Experimental colitis was induced in wild-type and PAD4KO mice via an intrarectal injection of TNBS. TNBS injection resulted in body weight loss, extensive colonic erosion, and ulceration in wildtype mice. However, these responses were significantly attenuated following the administration of Cl-amidine (an inhibitor of pan-PADs) and DNase I (an inhibitor of NET formation), in combination with PAD4KO in mice. TNBS-induced increases in myeloperoxidase activity, inflammatory cytokine expression, and NET formation in the colon were significantly reduced following the administration of Cl-amidine, DNase I injection, and PAD4KO. These findings suggest that NET formation contributes to the pathogenesis of TNBS-induced colitis via PAD4. Thus, PAD4 is a promising target for the treatment of inflammatory bowel disease.

Sub-anesthetic dose of esketamine decreases postoperative opioid self-administration after spine surgery: a retrospective cohort analysis

The use of intraoperative sub-anesthetic esketamine for postoperative analgesia is controversial. In this study, the impact of sub-anesthetic esketamine on postoperative opioid self-administration was determined. Patients who underwent spinal surgery with patient-controlled analgesia (PCA) from January 2019 to December 2021 were respectively screened for analysis. Postoperative PCA was compared between patients who received a sub-anesthetic esketamine dose and patients who were not treated with esketamine (non-esketamine group) with or without propensity score matching. Negative binomial regression analysis was used to identify factors associated with postoperative PCA. Patients who received intraoperative sub-anesthetic esketamine self-administered less PCA (P = 0.001). Azasetron, esketamine, and dexamethasone lowered the self-administration of PCA (IRR with 95% confidential interval, 0.789 [0.624, 0.993]; 0.581 [0.458, 0.741]; and 0.777 [0.627, 0.959], respectively). Fixation surgery and drinking were risk factors for postoperative PCA (1.737 [1.373, 2.188] and 1.332 [1.032, 1.737] for fixation surgery and drinking, respectively). An intraoperative sub-anesthetic dose of esketamine decreases postoperative opioid self-administration. Azasetron and dexamethasone also decrease postoperative opioid consumption. The study is registered at www.chictr.org.cn (ChiCTR2300068733).

TRPM8 inhibits substance P release from primary sensory neurons via PKA/GSK-3beta to protect colonic epithelium in colitis

Transient receptor potential melastatin 8 (TRPM8) is a cold sensory receptor in primary sensory neurons that regulates various neuronal functions. Substance P (SP) is a pro-inflammatory neuropeptide secreted by the neurons, and it aggravates colitis. However, the regulatory role of TRPM8 in SP release is still unclear. Our study aimed to investigate TRPM8's role in SP release from primary sensory neurons during colitis and clarify the effect of SP on colonic epithelium. We analyzed inflammatory bowel disease patients' data from the Gene Expression Omnibus dataset. Dextran sulfate sodium (DSS, 2.5%)-induced colitis in mice, mouse dorsal root ganglion (DRG) neurons, ND7/23 cell line, and mouse or human colonic organoids were used for this experiment. Our study found that TRPM8, TAC1 and WNT3A expression were significantly correlated with the severity of ulcerative colitis in patients and DSS-induced colitis in mice. The TRPM8 agonist (menthol) and the SP receptor antagonist (Aprepitant) can attenuate colitis in mice, but the effects were not additive. Menthol promoted calcium ion influx in mouse DRG neurons and inhibited the combination and phosphorylation of PKAca from the cAMP signaling pathway and GSK-3β from the Wnt/β-catenin signaling pathway, thereby inhibiting the effect of Wnt3a-driven β-catenin on promoting SP release in ND7/23 cells. Long-term stimulation with SP inhibited proliferation and enhanced apoptosis in both mouse and human colonic organoids. Conclusively, TRPM8 inhibits SP release from primary sensory neurons by inhibiting the interaction between PKAca and GSK-3β, thereby inhibiting the role of SP in promoting colonic epithelial apoptosis and relieving colitis.

Myenteric Plexus Immune Cell Infiltrations and Neurotransmitter Expression in Crohn's Disease and Ulcerative Colitis

BACKGROUND AND AIMS

Pain is a cardinal symptom in inflammatory bowel disease [IBD]. An important structure in the transduction of pain signalling is the myenteric plexus [MP]. Nevertheless, IBD-associated infiltration of the MP by immune cells lacks in-depth characterisation. Herein, we decipher intra- and periganglionic immune cell infiltrations in Crohn´s disease [CD] and ulcerative colitis [UC] and provide a comparison with murine models of colitis.

METHODS

Full wall specimens of surgical colon resections served to examine immune cell populations by either conventional immuno-histochemistry or immunofluorescence followed by either bright field or confocal microscopy. Results were compared with equivalent examinations in various murine models of intestinal inflammation.

RESULTS

Whereas the MP morphology was not significantly altered in IBD, we identified intraganglionic IBD-specific B cell- and monocyte-dominant cell infiltrations in CD. In contrast, UC-MPs were infiltrated by CD8+ T cells and revealed a higher extent of ganglionic cell apoptosis. With regard to the murine models of intestinal inflammation, the chronic dextran sulphate sodium [DSS]-induced colitis model reflected CD [and to a lesser extent UC] best, as it also showed increased monocytic infiltration as well as a modest B cell and CD8+ T cell infiltration.

CONCLUSIONS

In CD, MPs were infiltrated by B cells and monocytes. In UC, mostly CD8+ cytotoxic T cells were found. The chronic DSS-induced colitis in the mouse model reflected best the MP-immune cell infiltrations representative for IBD.

Transient receptor potential melastatin 2 is involved in trinitrobenzene sulfonic acid-induced acute and chronic colitis-associated fibrosis progression in mice

Crohn's disease, a chronic and recurrent gastrointestinal disease, frequently causes intestinal fibrosis. Transient receptor potential melastatin 2 (TRPM2), a non-selective cation channel, is activated by reactive oxygen species. This study investigated the role of TRPM2 in acute colitis and chronic colitis-associated fibrosis progression. Acute colitis and chronic colitis-associated fibrosis were induced in TRPM2-deficient (TRPM2KO) and wild-type (WT) mice through single and repeated intrarectal injections of 2,4,6-trinitrobenzene sulfonic acid (TNBS). Bone marrow-derived macrophages (BMDMs) from WT and TRPM2KO mice were stimulated using H2O2. In WT mice, a single TNBS injection induced acute colitis with upregulated inflammatory cytokines/chemokines and Th1/Th17-related cytokines, while repeated TNBS injections induced chronic colitis-associated fibrosis with upregulation of fibrogenic factors and Th2-related cytokines. Acute colitis and chronic colitis-associated fibrosis with cytokines/chemokine upregulation and fibrogenic factors were considerably suppressed in TRPM2KO mice. Treating BMDMs with H2O2 increased cytokine/chemokine expression and JNK, ERK, and p38 phosphorylation; however, these responses were significantly less in TRPM2KO than in WT mice. These findings suggest that TRPM2 contributes to acute colitis progression via Th1/Th17-mediated immune responses. Furthermore, TRPM2 may be directly involved in colitis-associated fibrosis induction, likely due to the regulation of Th2/TGF-β1-mediated fibrogenesis in addition to a consequence of acute colitis progression.

Effects of ondansetron exposure during ICU stay on outcomes of critically ill patients with sepsis: a cohort study

Background

Sepsis is a life-threatening disease with high morbidity and mortality, characterized by an inadequate systemic immune response to an initial stimulus. Whether the use of ondansetron (OND) during intensive care unit (ICU) stay is associated with the prognosis of sepsis patients remains unclear.

Methods

Critically ill patients with sepsis were extracted from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. Multivariate logistic regression and Cox regression analyses were used to explore the association between OND use and clinical outcomes after adjusting for confounders. Kaplan-Meier survival curve was used for survival analysis. Propensity score matching (PSM) and subgroup analysis were performed to further confirm the results.

Results

The OND-medication group showed reduced in-hospital mortality, 28-day and 90-day mortalities. The OR for in-hospital mortality was 0.80 (0.64-0.99) and HRs for 28-day mortality and 90-day mortality were 0.77 (0.64-0.92) and 0.83 (0.70-0.98), respectively. After PSM, the clinical outcomes remained consistent. In-hospital mortality was lower in the OND-medication group (28.1% vs. 35.8%, P= 0.044), as well as 28-day mortality (23.4% vs. 32.1%, P=0.022) and 90-day mortality (27.4% vs. 35.8%, P=0.035). The protective effect of OND in sepsis patients was relatively robust, independent of age, septic shock, vasopressin and mechanical ventilation. Additionally, the OND users had longer lengths of stay in ICU (6.9(3.1-13.2) vs. 5.1(2.5-11.0), P = 0.026) while no statistical differences were found in lengths of stay in hospital (P = 0.333).

Conclusion

OND exposure might be associated with lower in-hospital, 28-day, and 90-day mortality rates in critically ill patients with sepsis. This study indicated that OND might help improve the prognosis of patients with sepsis.

Chemotherapy-induced gastrointestinal toxicity: Pathogenesis and current management

Chemotherapy is the most common treatment for malignant tumors. However, chemotherapy-induced gastrointestinal toxicity (CIGT) has been a major concern for cancer patients, which reduces their quality of life and leads to treatment intolerance and even cessation. Nevertheless, prevention and treatment for CIGT are challenging, due to the prevalence and complexity of the condition. Chemotherapeutic drugs directly damage gastrointestinal mucosa to induce CIGT, including nausea, vomiting, anorexia, gastrointestinal mucositis, and diarrhea, etc. The pathogenesis of CIGT involves multiple factors, such as gut microbiota disorders, inflammatory responses and abnormal neurotransmitter levels, that synergistically contribute to its occurrence and development. In particular, the dysbiosis of gut microbiota is usually linked to abnormal immune responses that increases inflammatory cytokines' expression, which is a common characteristic of many types of CIGT. Chemotherapy-induced intestinal neurotoxicity is also a vital concern in CIGT. Currently, modern medicine is the dominant treatment of CIGT, however, traditional Chinese medicine (TCM) has attracted interest as a complementary and alternative therapy that can greatly alleviate CIGT. Accordingly, this review aimed to comprehensively summarize the pathogenesis and current management of CIGT using PubMed and Google Scholar databases, and proposed that future research for CIGT should focus on the gut microbiota, intestinal neurotoxicity, and promising TCM therapies, which may help to develop more effective interventions and optimize managements of CIGT.

Deficiency of leukotriene B4 receptor type 1 ameliorates ovalbumin-induced allergic enteritis in mice

Leukotriene B4 receptor type 1 (BLT1), a high-affinity receptor for leukotriene B4 (LTB4), plays an important role in inflammatory responses, including allergic airway inflammation. In this study, we examined the effect of genetic BLT1 deletion (BLT1KO) on ovalbumin (OVA)-induced allergic enteritis in mice to determine the pathogenic role of LTB4/BLT1 in allergic enteritis, a gastrointestinal form of food allergy. Repeated oral OVA challenges after sensitization with OVA and aluminium potassium sulphate induced allergic enteritis, characterized by systemic allergic symptoms (scratching, immobility and swelling), diarrhoea, colonic oedema and colonic goblet cell hyperplasia, accompanied by increased colonic peroxidase activity, colonic inflammatory cytokine expression and increased serum OVA-specific IgE levels. The severity of enteritis was significantly attenuated in BLT1KO mice compared with wild-type (WT) mice, without an increase in serum OVA-specific IgE levels. The accumulation of neutrophils, eosinophils, M2-macrophages, dendritic cells, CD4+ T cells and mast cells was observed in the colonic mucosa of allergic enteritis, and such accumulation was significantly lower in BLT1KO mice than in WT mice. BLT1 expression was upregulated and colocalized mostly in neutrophils and partly in eosinophils and dendritic cells in the colonic mucosa of allergic enteritis. These findings indicate that BLT1 deficiency ameliorates OVA-induced allergic enteritis in mice and that LTB4/BLT1 contributes to neutrophil and eosinophil accumulation in the allergic colonic mucosa. Therefore, BLT1 is a promising drug target for treating food allergies.

An overview of 5-HT3 receptor antagonists as a treatment option for irritable bowel syndrome with diarrhea

INTRODUCTION

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by abdominal pain, discomfort, and altered bowel habits, which affects the quality of life of approximately 10% of the worldwide population. IBS is classified into three types: IBS-D (diarrhea-predominant), IBS-C (constipation-predominant), and mixed or alternating IBS (IBS-M). Among potential interventions for IBS-D, the antagonism of the serotonin 5-HT₃ receptor has recently emerged as an effective treatment option. Serotonin (5-HT) is a neurotransmitter and an immunoregulatory factor which plays a key role in physiological and pathological processes of the human body, having an impact on intestinal motility and gland secretion, which assist in maintaining intestinal homeostasis.

AREAS COVERED

In this paper, the concept of 5-HT₃ antagonists in the treatment of individuals with IBS-D is discussed, with particular focus on mechanism of action and pre-clinical and clinical data. This study is based on pertinent papers that were retrieved by a selective search using relevant keywords in PubMed and ScienceDirect databases.

EXPERT OPINION

Recent clinical trial data has confirmed beyond doubt the value of 5-HT₃ antagonists. As for future directions, weak partial 5-HT₃ receptor agonism appears to be an appealing alternative to a silent antagonist for the treatment of IBS-D.

5-HT3 Receptors on Mitochondria Influence Mitochondrial Function

The 5-hydroxytryptamine 3 (5-HT₃) receptor belongs to the pentameric ligand-gated cation channel superfamily. Humans have five different 5-HT₃ receptor subunits: A to E. The 5-HT₃ receptors are located on the cell membrane, but a previous study suggested that mitochondria could also contain A subunits. In this article, we explored the distribution of 5-HT₃ receptor subunits in intracellular and cell-free mitochondria. Organelle prediction software supported the localization of the A and E subunits on the inner membrane of the mitochondria. We transiently transfected HEK293T cells that do not natively express the 5-HT₃ receptor with an epitope and fluorescent protein-tagged 5HT3A and 5HT3E subunits. Fluorescence microscopy and cell fractionation indicated that both subunits, A and E, localized to the mitochondria, while transmission electron microscopy revealed the location of the subunits on the mitochondrial inner membrane, where they could form heteromeric complexes. Cell-free mitochondria isolated from cell culture media colocalized with the fluorescent signal for A subunits. The presence of A and E subunits influenced changes in the membrane potential and mitochondrial oxygen consumption rates upon exposure to serotonin; this was inhibited by pre-treatment with ondansetron. Therefore, it is likely that the 5-HT₃ receptors present on mitochondria directly impact mitochondrial function and that this may have therapeutic implications.

Administration of Bifidobacterium pseudolongum suppresses the increase of colonic serotonin and alleviates symptoms in dextran sodium sulfate-induced colitis in mice

Previous studies suggested that altered gut serotonin (5-HT) signaling is implicated in the pathophysiology of inflammatory bowel disease (IBD). Indeed, 5-HT administration reportedly exacerbated the severity of murine dextran sodium sulfate (DSS)-induced colitis that mimics human IBD. Our recent study suggested that Bifidobacterium pseudolongum, one of the most predominant bifidobacterial species in various mammals, reduces the colonic 5-HT content in mice. The present study thus tested whether the administration of B. pseudolongum prevents DSS-induced colitis in mice. Colitis was induced by administering 3% DSS in drinking water in female BALB/c mice, and B. pseudolongum (10⁹ CFU/day) or 5-aminosalicylic acid (5-ASA, 200 mg/kg body weight) was intragastrically administered once daily throughout the experimental period. B. pseudolongum administration reduced body weight loss, diarrhea, fecal bleeding, colon shortening, spleen enlargement, and colon tissue damage and increased colonic mRNA levels of cytokine genes (Il1b, Il6, Il10, and Tnf) almost to an extent similar to 5-ASA administration in DSS-treated mice. B. pseudolongum administration also reduced the increase of colonic 5-HT content, whereas it did not alter the colonic mRNA levels of genes that encode the 5-HT synthesizing enzyme, 5-HT reuptake transporter, 5-HT metabolizing enzyme, and tight junction-associated proteins. We propose that B. pseudolongum is as beneficial against murine DSS-induced colitis as the widely used anti-inflammatory agent 5-ASA. However, further studies are needed to clarify the causal relationship between the reduced colonic 5-HT content and reduced severity of DSS-induced colitis caused by B. pseudolongum administration.

The effect of tropisetron on peripheral diabetic neuropathy: possible protective actions against inflammation and apoptosis

Diabetic peripheral neuropathy (DPN) is a common nerve disorder of diabetes. The aim of this study was to explore the protective effects of tropisetron in DPN. Type 1 diabetes was created by a single injection of streptozotocin (50 mg/kg, ip). Tropisetron (3 mg/kg, ip) was administered daily for 2 weeks. Our analysis showed that nerve fibers and their myelin sheaths were thinned with decreased myelinated fiber number in diabetic animals. The intensity of Bcl-2 staining decreased and the intensity of Bax staining increased in the sciatic nerves of diabetic rats by using immunohistochemical staining. Furthermore, diabetes significantly increased tumor necrosis factor-alpha, interleukin 1-β (TNFα and IL-1β) and Bax/Bcl-2 ratio in sciatic nerves of rats. However, intraperitoneal injection of tropisetron significantly reversed these alterations induced by diabetes. These findings suggest that tropisetron attenuates diabetes-induced peripheral nerve injury through its anti-inflammatory and anti-apoptotic effects, and may provide a novel therapeutic strategy to ameliorate the process of peripheral neuropathy in diabetes.

Tapping into 5-HT3 Receptors to Modify Metabolic and Immune Responses

5-hydroxytryptamine type 3 (5-HT₃) receptors are ligand gated ion channels, which clearly distinguish their mode of action from the other G-protein coupled 5-HT or serotonin receptors. 5-HT₃ receptors are well established targets for emesis and gastrointestinal mobility and are used as adjunct targets in treating schizophrenia. However, the distribution of these receptors is wider than the nervous system and there is potential that these additional sites can be targeted to modulate inflammatory and/or metabolic conditions. Recent progress in structural biology and pharmacology of 5-HT₃ receptors have provided profound insights into mechanisms of their action. These advances, combined with insights into clinical relevance of mutations in genes encoding 5-HT₃ subunits and increasing understanding of their implications in patient's predisposition to diseases and response to the treatment, open new avenues for personalized precision medicine. In this review, we recap on the current status of 5-HT₃ receptor-based therapies using a biochemical and physiological perspective. We assess the potential for targeting 5-HT₃ receptors in conditions involving metabolic or inflammatory disorders based on recent findings, underscoring the challenges and limitations of this approach.

Therapeutic effect of targeting Substance P on the progression of osteoarthritis

OBJECTIVES

Substance P (SP) modulates NK1 and has various functions such as regulation of pain response, bone metabolism, and angiogenesis, which are recognized as important factors in osteoarthritis (OA). We aimed to evaluate the therapeutic effect of targeting SP on OA progression.

METHODS

SP expression patterns were analysed histologically in articular cartilage and subchondral bone of human knees from OA patients and autopsy donors as non-OA samples and in mouse articular cartilage. Moreover, to examine the effect of SP on the progression of OA, we administered drugs to mice following the surgical destabilization of the medial meniscus: Phosphate-buffered saline (PBS), septide (NK1 receptor agonist), or aprepitant (NK1 receptor antagonist). Histological analysis and bone morphologic analysis using micro-computed tomography were performed.

RESULTS

In human analysis, the expression of SP in mild OA samples was significantly higher than that in severe OA, and that in healthy cartilage was significantly higher than that in OA. In mouse analysis, Osteoarthritis Research Society International scores in the septide group were significantly lower than those in the control group. Computed tomography analysis showed that the subchondral bone's epiphysis in the control group had sclerotic change, not observed in the septide group.

CONCLUSIONS

The administration of septide ameliorates OA progression through preventing subchondral bone sclerosis.

Post-inflammatory Abdominal Pain in Patients with Inflammatory Bowel Disease During Remission: A Comprehensive Review

Patients with inflammatory bowel disease often experience ongoing pain even after achieving mucosal healing (i.e., post-inflammatory pain). Factors related to the brain-gut axis, such as peripheral and central sensitization, altered sympatho-vagal balance, hypothalamic-pituitary-adrenal axis activation, and psychosocial factors, play a significant role in the development of post-inflammatory pain. A comprehensive study investigating the interaction between multiple predisposing factors, including clinical psycho-physiological phenotypes, molecular mechanisms, and multi-omics data, is still needed to fully understand the complex mechanism of post-inflammatory pain. Furthermore, current treatment options are limited and new treatments consistent with the underlying pathophysiology are needed to improve clinical outcomes.

Neurokinin-1 Antagonism Distinguishes the Role of Norepinephrine Transporter from Dopamine Transporter in Mediating Amphetamine Behaviors

BACKGROUND

Amphetamine (AMPH) and other psychostimulants act on the norepinephrine (NE) transporter (NET) and the dopamine (DA) transporter (DAT) and enhance NE and DA signaling. Both NET and DAT share anatomical and functional characteristics and are regulated similarly by psychostimulants and receptor-linked signaling pathways. We and others have demonstrated that NET and DAT are downregulated by AMPH and substance P/neurokinin-1 receptor (NK1R)-mediated protein kinase C pathway.

OBJECTIVES

Since both NET and DAT are downregulated by AMPH and NK1R activation and share high sequence homology, the objective of the study was to determine the catecholamine transporter specificity in NK1R modulation of AMPH-induced behaviors.

METHODS

The effect of NK1R antagonism on AMPH-induced conditioned place preference (CPP) as well as AMPH-induced NET and DAT downregulation was examined using NET and DAT knockout mice (NET-KO and DAT-KO) along with their wild-type littermates.

RESULTS

Aprepitant (5 mg/kg i.p.) significantly attenuated AMPH (2 mg/kg i.p.)-induced CPP in the wild-type and DAT-KO but not in the NET-KO. Locomotor activity measured during the post-conditioning test (in the absence of AMPH) showed higher locomotor activity in DAT-KO compared to wild-type or NET-KO. However, the locomotor activity of all 3 genotypes remained unchanged following aprepitant. Additionally, in the ventral striatum of wild-type, the AMPH-induced downregulation of NET function and surface expression but not that of DAT was attenuated by aprepitant.

CONCLUSIONS

The results from the current study demonstrate that aprepitant attenuates the expression of AMPH-induced CPP in DAT-KO mice but not in NET-KO mice suggesting a role for NK1R-mediated NET regulation in AMPH-induced behaviors.

Colonic Motility Is Improved by the Activation of 5-HT2B Receptors on Interstitial Cells of Cajal in Diabetic Mice

BACKGROUND & AIMS

Constipation is commonly associated with diabetes. Serotonin (5-HT), produced predominantly by enterochromaffin (EC) cells via tryptophan hydroxylase 1 (TPH1), is a key modulator of gastrointestinal (GI) motility. However, the role of serotonergic signaling in constipation associated with diabetes is unknown.

METHODS

We generated EC cell reporter Tph1-tdTom, EC cell-depleted Tph1-DTA, combined Tph1-tdTom-DTA, and interstitial cell of Cajal (ICC)-specific Kit-GCaMP6 mice. Male mice and surgically ovariectomized female mice were fed a high-fat high-sucrose diet to induce diabetes. The effect of serotonergic signaling on GI motility was studied by examining 5-HT receptor expression in the colon and in vivo GI transit, colonic migrating motor complexes (CMMCs), and calcium imaging in mice treated with either a 5-HT2B receptor (HTR2B) antagonist or agonist.

RESULTS

Colonic transit was delayed in males with diabetes, although colonic Tph1+ cell density and 5-HT levels were increased. Colonic transit was not further reduced in diabetic mice by EC cell depletion. The HTR2B protein, predominantly expressed by colonic ICCs, was markedly decreased in the colonic muscles of males and ovariectomized females with diabetes. Ca2+ activity in colonic ICCs was decreased in diabetic males. Treatment with an HTR2B antagonist impaired CMMCs and colonic motility in healthy males, whereas treatment with an HTR2B agonist improved CMMCs and colonic motility in males with diabetes. Colonic transit in ovariectomized females with diabetes was also improved significantly by the HTR2B agonist treatment.

CONCLUSIONS

Impaired colonic motility in mice with diabetes was improved by enhancing HTR2B signaling. The HTR2B agonist may provide therapeutic benefits for constipation associated with diabetes.

Role of transient receptor potential vanilloid subtype 2 in lower oesophageal sphincter in rat acid reflux oesophagitis

Gastroesophageal reflux disease (GERD) is a common gastrointestinal disorder. In the present study, we investigated TRP vanilloid subfamily member 2 (TRPV2) expression in lower oesophageal sphincter (LES) and its involvement in acid reflux oesophagitis in rats. Expression of TRPV2 and nerve growth factor mRNAs was significantly enhanced in LES of rats with reflux oesophagitis compared with normal rats. TRPV2 was mainly expressed in inhibitory motor neurons, and partly in intrinsic and extrinsic primary afferent neurons, and macrophages in LES of normal and reflux oesophagitis rats. Number of TRPV2-immunopositive nerve fibres was significantly increased, but that of nNOS-, CGRP-, and PGP9.5-nerve fibres was not changed in reflux oesophagitis compared with normal group. Probenecid produced nitric oxide production and relaxation in LES and this response was significantly enhanced in oesophagitis compared with normal group. Probenecid-induced relaxant effect was blocked by a TRPV2 inhibitor, tranilast, and a NOS inhibitor, NG-nitro-l-arginine methyl ester, in reflux oesophagitis rats. Oral administration of tranilast significantly improved body weight loss, oesophageal lesions, and epithelial thickness in oesophagitis model. These results suggest that up-regulation of TRPV2 in inhibitory motor neurons is involved in LES relaxation in oesophagitis model. TRPV2 inhibition might be beneficial for treatment of GERD.

Protective Effect of TRPM8 against Indomethacin-Induced Small Intestinal Injury via the Release of Calcitonin Gene-Related Peptide in Mice

Transient receptor potential melastatin 8 (TRPM8) is a non-selective cation channel activated by mild cooling and chemical agents including menthol. Nonsteroidal anti-inflammatory drugs have antipyretic, analgesic effects, and they can cause stomach and small intestinal injury. The current study investigated the role of TRPM8 in the pathogenesis of indomethacin-induced small intestinal injury. In male TRPM8-deficient (TRPM8KO) and wild-type (WT) mice, intestinal injury was induced via the subcutaneous administration of indomethacin. In addition, the effect of WS-12, a specific TRPM8 agonist, was examined in TRPM8KO and WT mice with indomethacin-induced intestinal injury. TRPM8KO mice had a significantly higher intestinal ulcerogenic response to indomethacin than WT mice. The repeated administration of WS-12 significantly attenuated the severity of intestinal injury in WT mice. However, this response was abrogated in TRPM8KO mice. Furthermore, in TRPM8-enhanced green fluorescent protein (EGFP) transgenic mice, which express EGFP under the direction of TRPM8 promoter, the EGFP signals in the indomethacin-treated intestinal mucosa were upregulated. Further, the EGFP signals were commonly found in calcitonin gene-related peptide (CGRP)-positive sensory afferent neurons and partly colocalized with substance P (SP)-positive neurons in the small intestine. The intestinal CGRP-positive neurons were significantly upregulated after the administration of indomethacin in WT mice. Nevertheless, this response was abrogated in TRPM8KO mice. In contrast, indomethacin increased the expression of intestinal SP-positive neurons in not only WT mice but also TRPM8KO mice. Thus, TRPM8 has a protective effect against indomethacin-induced small intestinal injury. This response may be mediated by the upregulation of CGRP, rather than SP.

Ultrasonographic evaluation of the effects of the administration of neostigmine and metoclopramide on duodenal, cecal, and colonic contractility in Arabian horses: A comparative study

Background and Aim

As means for enhancing gastrointestinal (GI) motility, prokinetics have previously been evaluated in different breeds of horses with varying success. No previous studies were conducted to evaluate the effect of prokinetics on the intestinal tract of Arabian horses breed. Using B-mode ultrasound in the quantification of intestinal contractility, this study aimed to compare the impact of neostigmine and metoclopramide on the intestinal motility of healthy Arabian horses.

Materials and Methods

Twenty-one clinically healthy Arabian horses were equally distributed into three groups. The control group was administered with 5 mL normal saline intramuscularly (IM). The second group was administered with neostigmine (0.044 mg/kg body weight [BW], IM), and the third group was administered with metoclopramide (0.25 mg/kg BW, IM). Duodenal, cecal, and colonic contractions were counted through ultrasonography for 3 min (pre-administration and 15, 30, 60, 120, and 180 min post-administration).

Results

In the neostigmine group, a significant (p<0.05) increase in duodenal, cecal, and colonic contractions was observed 15 min post-administration compared with that in the control group (15±1.0, 11.33±1.53, and 12.33±2.31 vs. 11.0±2.0, 6.33±0.58, and 5.33±0.58 contractions per 3 min, respectively), continuing to 60 min post-administration for the duodenum and cecum and 120 min for colon and then returning to the normal; however, the metoclopramide group showed a significant (p<0.05) increase only in cecal and colonic contractions 60 min post-administration compared with the control group (11.0±1.0 and 12.33±0.58 vs. 6±1.0 and 5.67±0.58 contractions per 3 min, respectively), continuing until the end of the experiment. Excessive sweating, excitation, and straining were recorded following the administration of neostigmine, whereas no side effects were observed in the metoclopramide group.

Conclusion

Neostigmine improves duodenal, cecal, and colonic contractions in healthy adult Arabian horses, whereas metoclopramide only improves cecal and colonic contractions. Metoclopramide appears to be safer and longer acting than neostigmine in the Arabian horse breed. Ultrasonography is a valuable noninvasive tool for the quantification of intestinal contractility. Future studies should consider the use of various dosages of metoclopramide and administration routes and investigate its impact on horses with GI transit disorders and inclusion in colic post-operative care.

5-HT3 Receptor Antagonists in Neurologic and Neuropsychiatric Disorders: The Iceberg Still Lies beneath the Surface

5-HT₃ receptor antagonists, first introduced to the market in the mid-1980s, are proven efficient agents to counteract chemotherapy-induced emesis. Nonetheless, recent investigations have shed light on unappreciated dimensions of this class of compounds in conditions with an immunoinflammatory component as well as in neurologic and psychiatric disorders. The promising findings from multiple studies have unveiled several beneficial effects of these compounds in multiple sclerosis, stroke, Alzheimer disease, and Parkinson disease. Reports continue to uncover important roles for 5-HT₃ receptors in the physiopathology of neuropsychiatric disorders, including depression, anxiety, drug abuse, and schizophrenia. This review addresses the potential of 5-HT₃ receptor antagonists in neurology- and neuropsychiatry-related disorders. The broad therapeutic window and high compliance observed with these agents position them as suitable prototypes for the development of novel pharmacotherapeutics with higher efficacy and fewer adverse effects.

Electroacupuncture inhibits visceral pain via adenosine receptors in mice with inflammatory bowel disease

To investigate the involvement of peripheral adenosine receptors in the effect of electroacupuncture (EA) on visceral pain in mice with inflammatory bowel disease (IBD). 2,4,6-Trinitrobenzene sulfonic acid (TNBS) was used to induce the visceral pain model. EA (1 mA, 2 Hz, 30 min) treatment was applied to bilateral acupoints "Dachangshu" (BL25) 1 day after TNBS injection once daily for 7 consecutive days. Von Frey filaments were used to measure the mechanical pain threshold. Western blot was used to detect the protein expression levels of adenosine 1 receptor (A1R), adenosine 2a receptor (A2aR), adenosine 2b receptor (A2bR), adenosine 3 receptor (A3R), substance P (SP), and interleukin 1 beta (IL-1β) in colon tissue. EA significantly ameliorated the disease-related indices and reduced the expression of SP and IL-1β in the colon tissues of mice with IBD. EA increased the expression of A1R, A2aR, and A3R and decreased the expression of A2bR in the colon tissue. Furthermore, the administration of adenosine receptor antagonists influenced the effect of EA. EA can inhibit the expression of the inflammatory factors SP and IL-1β by regulating peripheral A1, A2a, A2b, and A3 receptors, thus inhibiting visceral pain in IBD mice.

Intestinal Microbiota Mediates the Susceptibility to Polymicrobial Sepsis-Induced Liver Injury by Granisetron Generation in Mice

Sepsis-induced liver injury is recognized as a key problem in intensive care units. The gut microbiota has been touted as an important mediator of liver disease development; however, the precise roles of gut microbiota in regulating sepsis-induced liver injury are unknown. Here, we aimed to investigate the role of the gut microbiota in sepsis-induced liver injury and the underlying mechanism. Cecal ligation and puncture (CLP) was used to induce polymicrobial sepsis and related liver injury. Fecal microbiota transplantation (FMT) was used to validate the roles of gut microbiota in these pathologies. Metabolomics analysis was performed to characterize the metabolic profile differences between sepsis-resistant (Res; survived to 7 days after CLP) and sepsis-sensitive (Sen; moribund before or approximately 24 hours after CLP) mice. Mice gavaged with feces from Sen mice displayed more-severe liver damage than did mice gavaged with feces from Res mice. The gut microbial metabolic profile between Sen and Res mice was different. In particular, the microbiota from Res mice generated more granisetron, a 5-hydroxytryptamine 3 (5-HT₃ ) receptor antagonist, than the microbiota from Sen mice. Granisetron protected mice against CLP-induced death and liver injury. Moreover, proinflammatory cytokine expression by macrophages after lipopolysaccharide (LPS) challenge was markedly reduced in the presence of granisetron. Both treatment with granisetron and genetic knockdown of the 5-HT_3A receptor in cells suppressed nuclear factor kappa B (NF-кB) transactivation and phosphorylated p38 (p-p38) accumulation in macrophages. Gut microbial granisetron levels showed a significantly negative correlation with plasma alanine aminotransferase (ALT)/aspartate aminotransferase (AST) levels in septic patients. Conclusion: Our study indicated that gut microbiota plays a key role in the sensitization of sepsis-induced liver injury and associates granisetron as a hepatoprotective compound during sepsis development.

Obesity, Motility, Diet, and Intestinal Microbiota-Connecting the Dots

PURPOSE OF REVIEW

The goal of the present review is to explore the relationship between dietary changes and alterations in gut microbiota that contribute to disorders of gut motility and obesity.

RECENT FINDINGS

We review the microbiota changes that are seen in obesity, diarrhea, and constipation and look at potential mechanisms of how dysbiosis can predispose to these. We find that microbial metabolites, particularly short chain fatty acids, can lead to signaling changes in the host enterocytes. Microbial alteration leading to both motility disorders and obesity may be mediated by the release of hormones including glucagon-like peptides 1 and 2 (GLP-1, GLP-2) and polypeptide YY (PYY). These pathways provide avenues for microbiota-targeted interventions that can treat both disorders of motility and obesity. In summary, multiple mechanisms contribute to the interplay between the microbial dysbiosis, obesity, and dysmotility.

A colon-specific prodrug of metoclopramide ameliorates colitis in an experimental rat model

Background

We examined whether metoclopramide (MCP), a modulator of dopamine and serotonin receptors, alleviated colitis and had synergistic effects when coadministered with 5-aminosalicylic acid (5-ASA) in an experimental model of colitis.

Methods

MCP azo-linked to 5-ASA (5-[4-chloro-2-{2-(diethylamino)ethylcarbamoyl}– 1-methoxyphenyl]azosalicylic acid, MCP-azo-ASA) was synthesized, where 5-ASA was used as a colon-targeting carrier and an anti-colitic agent, and the ability of MCP-azo-ASA to target the colon in vitro and in vivo was evaluated.

Results

Our results indicate that MCP-azo-ASA was cleaved to MCP and 5-ASA in the cecal contents, but not in the contents of the small intestine. Oral gavage with equimolar concentrations of MCP-azo-ASA and sulfasalazine (SSZ, a colon-specific prodrug of 5-ASA widely used clinically) demonstrated that the two prodrugs delivered comparable amounts of 5-ASA to the cecum. MCP was barely detected in the blood after oral gavage with MCP-azo-ASA. In a rat model of 2,4-dinitrobenzene sulfonic acid hydrate (DNBS)-induced colitis, MCP-azo-ASA alleviated colonic damage in a dose-dependent manner. Moreover, MCP-azo-ASA reduced the concentrations of inflammatory mediators in the inflamed colon. At low equimolar doses, MCP-azo-ASA, but not SSZ, resulted in significant anti-colitic effects, which indicates that MCP has anti-colitic activity. MCP-azo-ASA had anti-colitic effects equal to those of SSZ at high equimolar doses.

Conclusion

Thus, our results indicate that MCP-azo-ASA is a colon-specific prodrug of MCP. Targeted delivery of MCP to the colon ameliorated DNBS-induced colitis in rats, and we did not observe any synergistic effects of MCP after co-delivery with 5-ASA.

Serotonin 3 receptor signaling regulates 5-fluorouracil-mediated apoptosis indirectly via TNF-α production by enhancing serotonin release from enterochromaffin cells

Antagonists of the 5-hydroxytryptamine (serotonin) 3 receptor (5-HT₃R) have anti-inflammatory and anti-apoptotic activities, but the detailed, underlying mechanisms are not well understood. We focused on anti-apoptotic activities via 5-HT₃R signaling to clarify the underlying mechanisms. Mice were administered 5-fluorouracil (5-FU), which induced apoptosis in intestinal epithelial cells. Coadministration with 5-HT₃R antagonists or agonists tended to decrease or increase the number of apoptotic cells, respectively. In serotonin 3A receptor (5-HT_3AR) null (HTR3A^-/-) mice, the number of apoptotic cells induced by 5-FU was decreased compared with that in wild-type (WT) mice. Bone marrow (BM) transplantation was performed to determine if BM-derived immune cells regulated 5-FU-induced apoptosis, but they were found to be unrelated to this process. Data from 5-HT_3AR/enhanced green fluorescent protein reporter mice revealed that 50% of enterochromaffin (EC) cells expressed 5-HT_3AR, but the number of apoptotic cells induced by 5-FU in the intestinal crypt organoids of HTR3A^-/- mice was not altered compared with WT mice. In contrast, plasma 5-HT concentrations in WT mice but not in HTR3A^-/- mice administered 5-FU were increased significantly. In conclusion, 5-HT₃R signaling may enhance 5-HT release, possibly from EC cells intravascularly, or paracrine, resulting in increases in plasma 5-HT concentration, which in turn, enhances apoptotic activities induced by 5-FU.-Mikawa, S., Kondo, M., Kaji, N., Mihara, T., Yoshitake, R., Nakagawa, T., Takamoto, M., Nishimura, R., Shimada, S., Ozaki, H., Hori, M. Serotonin 3 receptor signaling regulates 5-fluorouracil-mediated apoptosis indirectly via TNF-α production by enhancing serotonin release from enterochromaffin cells.

Colitis-induced alterations in response properties of visceral nociceptive neurons in the rat caudal medulla oblongata and their modulation by 5-HT3 receptor blockade

There is considerable clinical and experimental evidence that intestinal inflammation is associated with altered visceral nociceptive processing in the spinal cord and brain, but the underlying neuronal mechanisms, especially acting at the supraspinal level, remain unclear. Considering that the caudal ventrolateral medulla (CVLM) and the nucleus tractus solitarius (NTS) are the first sites for supraspinal processing of visceral pain signals, in the present study we evaluated the experimental colitis-induced changes in response properties of CVLM and NTS medullary neurons to noxious colorectal distension (CRD) in urethane-anesthetized adult male Wistar rats. To determine if gut inflammation alters the 5-HT₃ receptor-dependent modulation of visceral pain-related CVLM and NTS cells, we examined the effects of intravenously administered selective 5-HT₃ antagonist granisetron on ongoing and CRD-evoked activity of CVLM and NTS neurons in healthy control and colitic animals. In the absence of colonic pathology, the CVLM neurons were more excited by noxious CRD that the NTS cells, which demonstrated a greater tendency to be inhibited by the stimulation. The difference was eliminated after the development of colitis due to the increase in the proportion of CRD-excited neurons in both medullary regions associated with enhanced magnitude of the neuronal nociceptive responses. Intravenous granisetron (1 or 2 mg/kg) produced the dose-dependent suppression of the ongoing and evoked firing of CRD-excited cells within both the CVLM and NTS in normal conditions as well as was able to substantially reduce excitability of the caudal medullary neurons in the presence of colonic inflammation, arguing for the potential efficacy of the 5-HT₃ receptor blockade with granisetron against both acute and inflammatory abdominal pain. Taken together, the data obtained can contribute to a deeper understanding of supraspinal serotonergic mechanisms responsible for the persistence of visceral hypersensitivity and hyperalgesia triggered by colonic inflammation.

Communication Between Enteric Neurons, Glia, and Nociceptors Underlies the Effects of Tachykinins on Neuroinflammation

Background & Aims

Tachykinins are involved in physiological and pathophysiological mechanisms in the gastrointestinal tract. The major sources of tachykinins in the gut are intrinsic enteric neurons in the enteric nervous system and extrinsic nerve fibers from the dorsal root and vagal ganglia. Although tachykinins are important mediators in the enteric nervous system, how they contribute to neuroinflammation through effects on neurons and glia is not fully understood. Here, we tested the hypothesis that tachykinins contribute to enteric neuroinflammation through mechanisms that involve intercellular neuron-glia signaling.

Methods

We used immunohistochemistry and quantitative real-time polymerase chain reaction, and studied cellular activity using transient-receptor potential vanilloid-1 (TRPV1)tm1(cre)Bbm/J::Polr2atm1(CAG-GCaMP5g,-tdTomato)Tvrd and Sox10CreERT2::Polr2atm1(CAG-GCaMP5g,-tdTomato)Tvrd mice or Fluo-4. We used the 2,4-di-nitrobenzene sulfonic acid (DNBS) model of colitis to study neuroinflammation, glial reactivity, and neurogenic contractility. We used Sox10::CreERT2+/-/Rpl22tm1.1Psam/J mice to selectively study glial transcriptional changes.

Results

Tachykinins are expressed predominantly by intrinsic neuronal varicosities whereas neurokinin-2 receptors (NK2Rs) are expressed predominantly by enteric neurons and TRPV1-positive neuronal varicosities. Stimulation of NK2Rs drives responses in neuronal varicosities that are propagated to enteric glia and neurons. Antagonizing NK2R signaling enhanced recovery from colitis and prevented the development of reactive gliosis, neuroinflammation, and enhanced neuronal contractions. Inflammation drove changes in enteric glial gene expression and function, and antagonizing NK2R signaling mitigated these changes. Neurokinin A-induced neurodegeneration requires glial connexin-43 hemichannel activity.

Conclusions

Our results show that tachykinins drive enteric neuroinflammation through a multicellular cascade involving enteric neurons, TRPV1-positive neuronal varicosities, and enteric glia. Therapies targeting components of this pathway could broadly benefit the treatment of dysmotility and pain after acute inflammation in the intestine.

Tropisetron attenuates lipopolysaccharide induced neuroinflammation by inhibiting NF-κB and SP/NK1R signaling pathway

Tropisetron, an antagonist of serotonin type 3 receptors (5-HT₃Rs), has been investigated in colonic inflammatory process. Since substance P/neurokinin 1 receptor (SP/NK1R) signaling pathway plays a key role in several sensory neuronal inflammatory. We evaluated the anti-inflammatory activity of tropisetron in mice cerebral cortex, and discovered that it was a potential inhibitor in LPS-mediated neuron inflammation through SP/NK1R signaling pathway. We found that tropisetron significantly reduced the increased number of iba-1 positive microglia, down-regulated the gene transcription and protein expression of IL-1β,IL-6 and TNF-α in LPS stimulated cerebral cortex. To characterize the inhibitory mechanism of tropisetron at the SP response in inflammation, we further examined the effect of tropisetron on NF-κB and SP/NK1R signaling pathway in the process of mice cerebral cortex inflammation. We found that tropisetron inhibited the gene transcription and protein expression of NF-κB, SP, NK1R via inhibiting 5-HT₃R activity. These findings might provide new insights into the anti-inflammatory activities of 5-HT₃R inhibitor tropisetron, which would be the interaction of serotonin receptor signaling and SP/NK1R pathway. These might highlight their potential to design novel therapeutic strategies to manage inflammatory diseases.

Manipulation of intestinal dysbiosis by a bacterial mixture ameliorates loperamide-induced constipation in rats

Constipation has a significant influence on quality of life. Patients with constipation have slow waves in their gastrointestinal smooth muscles and less faecal water contents, which are closely associated with down-regulation of the interstitial cells of Cajal (ICC) in the gastrointestinal muscles and the aquaporin protein AQP3 expressed in colon epithelial cells. Recent studies supported that patients with constipation have altered intestinal microbial structures compared with healthy controls. Intestinal dysbiosis might be one possible pathophysiological mechanism causing constipation. Bacterial strains, such as Lactobacillus spp., have shown many beneficial effects on the amelioration of constipation. However, few studies reported the structural changes of intestinal microbiota post-intervention of probiotics. In this study, a bacterial mixture was administrated to rats with loperamide-induced constipation. Effects of the bacterial mixture on small intestine transit (SIT), faecal water content, and the intestinal microbiome in rats were evaluated. Meanwhile, we investigated several factors involved in signalling pathways that regulate function of ICC and expression of AQP3 to discuss the possible underlying molecular mechanisms. Intervention of the bacterial mixture improved SIT and faecal water content in constipated rats. The up-regulation of C-kit/SP signalling pathways in ICC and AQP3 significantly contributed to improvements. These changes were closely associated with the manipulation of intestinal dysbiosis in constipated rats. Furthermore, our results revealed the important role of intestinal microbiota in affecting gut motility through regulation of serotonin biosynthesis. This monoamine neurotransmitter, secreted from enterochromaffin cells, up-regulated both substance P/neurokinin 1 receptors pathway of ICC and the expression of AQP3 in intestinal epithelial cells. Our study suggested that the disrupted microbiome in patients could be a potential therapeutic target for the improvement of constipation.

The anti-inflammatory action of maropitant in a mouse model of acute pancreatitis

The neurokinin 1 receptor (NK1R) plays an important role in the pathogenesis of acute pancreatitis (AP). Maropitant is an NK1R antagonist that is widely used as an antiemetic in dogs and cats. In the present study, we investigated the anti-inflammatory action of maropitant in a mouse model of AP. AP was induced in BALB/c mice by intraperitoneal administration of cerulein, and maropitant was administered subcutaneously at a dose of 8 mg/kg. We assessed the mRNA expression levels of NK1R and substance P (SP) in the pancreatic tissue via real-time reverse transcription polymerase chain reaction. In addition, the effect of maropitant on plasma amylase, lipase, and interleukin-6 (IL-6) levels was measured in each mouse. Inflammatory cell infiltration in the pancreas was assessed by myeloperoxidase (MPO) staining. Our results showed that AP induction significantly elevated the mRNA expression of SP in the pancreatic tissue. Treatment with maropitant significantly lowered plasma amylase and IL-6 levels. In addition, treatment with maropitant inhibited the infiltration of MPO-positive cells in the pancreas. The present study suggests that maropitant possesses an anti-inflammatory activity, in addition to its antiemetic action.

Transient receptor potential vanilloid 4 channel regulates vascular endothelial permeability during colonic inflammation in dextran sulphate sodium-induced murine colitis

BACKGROUND AND PURPOSE

The transient receptor potential vanilloid 4 (TRPV4) channel is a non-selective cation channel involved in physical sensing in various tissue types. The present study aimed to elucidate the function and expression of TRPV4 channels in colonic vascular endothelial cells during dextran sulphate sodium (DSS)-induced colitis.

EXPERIMENTAL APPROACH

The role of TRPV4 channels in the progression of colonic inflammation was examined in a murine DSS-induced colitis model using immunohistochemical analysis, Western blotting and Evans blue dye extrusion assay.

KEY RESULTS

DSS-induced colitis was significantly attenuated in TRPV4-deficient (TRPV4 KO) as compared to wild-type mice. Repeated intrarectal administration of GSK1016790A, a TRPV4 agonist, exacerbated the severity of DSS-induced colitis. Bone marrow transfer experiments demonstrated the important role of TRPV4 in non-haematopoietic cells for DSS-induced colitis. DSS treatment up-regulated TRPV4 expression in the vascular endothelia of colonic mucosa and submucosa. DSS treatment increased vascular permeability, which was abolished in TRPV4 KO mice. This DSS-induced increase in vascular permeability was further enhanced by i.v. administration of GSK1016790A, and this effect was abolished by the TRPV4 antagonist RN1734. TRPV4 was co-localized with vascular endothelial (VE)-cadherin, and VE-cadherin expression was decreased by repeated i.v. administration of GSK1016790A during colitis. Furthermore, GSK106790A decreased VE-cadherin expression in mouse aortic endothelial cells exposed to TNF-α.

CONCLUSION AND IMPLICATIONS

These findings indicate that an up-regulation of TRPV4 channels in vascular endothelial cells contributes to the progression of colonic inflammation by increasing vascular permeability. Thus, TRPV4 is an attractive target for the treatment of inflammatory bowel diseases.

Differential effects of aprepitant, a clinically used neurokinin-1 receptor antagonist on the expression of conditioned psychostimulant versus opioid reward

RATIONALE

Neurokinin-1 receptor (NK1R) signaling modulates behaviors associated with psychostimulants and opioids. Psychostimulants, such as amphetamine (AMPH) and cocaine, bind to monoamine transporters and alter their functions. Both dopamine and norepinephrine transporters are regulated by NK1R activation suggesting a role for NK1R mediated catecholamine transporter regulation in psychostimulant-mediated behaviors.

OBJECTIVES

The effect of in vivo administration of aprepitant (10 mg/kg) on the expression of AMPH (0.5 and 2 mg/kg) and cocaine (5 and 20 mg/kg)-induced conditioned place preference (CPP) as well as locomotor activation was examined in C57BL/6J mice. The effect of aprepitant on morphine (1 and 5 mg/kg)-induced CPP was also examined to identify the specific actions of aprepitant on psychostimulant versus opioid-induced behaviors.

RESULTS

Aprepitant administration significantly attenuated the CPP expression and locomotor activation produced by AMPH and cocaine. In contrast, aprepitant significantly enhanced the expression of CPP produced by morphine while significantly suppressing the locomotor activity of the mice conditioned with morphine. Aprepitant by itself did not induce significant CPP or conditioned place aversion or locomotor activation or suppression.

CONCLUSIONS

Attenuation of AMPH or cocaine-induced CPP and locomotor activation by aprepitant suggests a role for NK1R signaling in psychostimulant-mediated behaviors. Stimulation of morphine-induced CPP expression and suppression of locomotor activity of morphine-conditioned mice suggest differential effects of NK1R antagonism on conditioned psychostimulant versus opioid reward. Collectively, these findings indicate that clinically used NK1R antagonist, aprepitant may serve as a potential therapeutic agent in the treatment of psychostimulant abuse.

Xenin Augments Duodenal Anion Secretion via Activation of Afferent Neural Pathways

Xenin-25, a neurotensin (NT)-related anorexigenic gut hormone generated mostly in the duodenal mucosa, is believed to increase the rate of duodenal ion secretion, because xenin-induced diarrhea is not present after Roux-en-Y gastric bypass surgery. Because the local effects of xenin on duodenal ion secretion have remained uninvestigated, we thus examined the neural pathways underlying xenin-induced duodenal anion secretion. Intravenous infusion of xenin-8, a bioactive C-terminal fragment of xenin-25, dose dependently increased the rate of duodenal HCO₃^- secretion in perfused duodenal loops of anesthetized rats. Xenin was immunolocalized to a subset of enteroendocrine cells in the rat duodenum. The mRNA of the xenin/NT receptor 1 (NTS1) was predominantly expressed in the enteric plexus, nodose and dorsal root ganglia, and in the lamina propria rather than in the epithelium. The serosal application of xenin-8 or xenin-25 rapidly and transiently increased short-circuit current in Ussing-chambered mucosa-submucosa preparations in a concentration-dependent manner in the duodenum and jejunum, but less so in the ileum and colon. The selective antagonist for NTS1, substance P (SP) receptor (NK1), or 5-hydroxytryptamine (5-HT)₃, but not NTS2, inhibited the responses to xenin. Xenin-evoked Cl^- secretion was reduced by tetrodotoxin (TTX) or capsaicin-pretreatment, and abolished by the inhibitor of TTX-resistant sodium channel Nav1.8 in combination with TTX, suggesting that peripheral xenin augments duodenal HCO₃^- and Cl^- secretion through NTS1 activation on intrinsic and extrinsic afferent nerves, followed by release of SP and 5-HT. Afferent nerve activation by postprandial, peripherally released xenin may account for its secretory effects in the duodenum.

5-HT3 receptors promote colonic inflammation via activation of substance P/neurokinin-1 receptors in dextran sulphate sodium-induced murine colitis

BACKGROUND AND PURPOSE

5-HT (serotonin) regulates various physiological functions, both directly and via enteric neurons. The present study investigated the role of endogenous 5-HT and 5-HT3 receptors in the pathogenic mechanisms involved in colonic inflammation, especially in relation to substance P (SP) and the neurokinin-1 (NK1 ) receptor.

EXPERIMENTAL APPROACH

The effects of 5-HT3 and NK1 receptor antagonists were examined in dextran sulphate sodium (DSS)-induced colitis in mice. Inflammatory mediator expression and the distribution of 5-HT3 and NK1 receptors were also determined.

KEY RESULTS

Daily administration of ramosetron and ondansetron (5-HT3 antagonists) dose-dependently attenuated the severity of DSS-induced colitis and up-regulation of inflammatory mediator expression. Immunohistochemical analysis showed 5-HT3 receptors are mainly expressed in vesicular ACh transporter-positive cholinergic nerve fibres in normal colon. DSS increased the number of colonic nerve fibres that were double positive for 5-HT3 receptors and SP but not of those that were double positive for 5-HT3 receptors and vesicular ACh transporter. DSS increased colonic SP levels and SP-positive nerve fibres; these responses were attenuated by ramosetron. DSS-induced colitis and up-regulation of inflammatory mediators were attenuated by aprepitant, an NK1 antagonist. Immunohistochemical studies further revealed that DSS treatment markedly increased NK1 receptor expression in CD11b-positive cells.

CONCLUSIONS AND IMPLICATIONS

These findings indicate that the 5-HT/5-HT3 receptor and SP/NK1 receptor pathways play pathogenic roles in colonic inflammation. 5-HT acts via 5-HT3 receptors to up-regulate inflammatory mediators and promote colonic inflammation. These effects may be further mediated by activation of macrophage NK1 receptors via SP released from 5-HT3 receptor-positive nerve fibres.