Immunohistochemical characterization of transient receptor potential vanilloid types 2 and 1 in a trinitrobenzene sulfonic acid-induced rat colitis model with visceral hypersensitivity.

Transient receptor potential vanilloid type 2 (TRPV2) and type 1 (TRPV1) are originally identified as heat-sensitive TRP channels. We compared the expression patterns of TRPV2 and TRPV1 in the rat distal colon and extrinsic primary afferent neurons, and investigated their roles in visceral hypersensitivity in 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis rats. Both TRPV2 and TRPV1 expressions in the colon, dorsal root ganglion (DRG), and nodose ganglion (NG) were significantly upregulated in the TNBS-induced colitis model. TRPV2 cell bodies co-localized with the intrinsic primary afferent marker NeuN and the inhibitory motor neuronal marker nNOS in the myenteric plexus. TRPV2 expressions were further detected in the resident macrophage marker ED2 in the mucosa. In contrast, no TRPV1-expressing cell bodies were detected in the myenteric plexus. Both TRPV2- and TRPV1-positive cell bodies in the DRG and NG were double-labeled with the neuronal retrograde tracer fluorescent fluorogold. Large- and medium-sized TRPV2-positive neurons were labeled with the A-fiber marker NF200, calcitonin gene-related peptide (CGRP), and substance P (SP) in the DRG while small-sized TRPV1-positive neurons were labeled with the C-fiber markers IB4, CGRP, and SP. TRPV2- and TRPV1-positive NG neurons were labeled with NF200 and IB4. TNBS treatment increased p-ERK1/2-positive cells in TRPV2 and TRPV1 neurons but did not affect the TRPV2 and TRPV1 subpopulations in the DRG and NG. Both TRPV2 and TRPV1 antagonists significantly alleviated visceral hypersensitivity in TNBS-induced colitis model rats. These findings suggest that intrinsic/extrinsic TRPV2- and extrinsic TRPV1-neurons contribute to visceral hypersensitivity in an experimental colitis model.

Allyl isothiocyanate, an activator of TRPA1, increases gastric mucosal blood flow through calcitonin gene-related peptide and adrenomedullin in anesthetized rats.

Allyl isothiocyanate (AITC) activates transient receptor potential ankyrin 1 (TRPA1) channel, which is involved in the control of intestinal mucosal blood flow. However, the mechanism underlying the increased gastric mucosal blood flow (GMBF) in response to AITC remains unknown. We examined the effect of AITC on GMBF in the ex vivo stomachs of normal and sensory deafferented rats using a laser Doppler flowmeter. Mucosal application of AITC increased GMBF in a concentration-dependent manner. Repeated AITC exposure resulted in a marked desensitization. The increased GMBF response induced by AITC was entirely blocked by co-application of TRPA1 channel blockers HC-030031 or AP-18. Increased GMBF in response to AITC was significantly attenuated by chemical deafferentation following systemic capsaicin injections (total dose: 100 mg/kg). In contrast, increased GMBF responses to capsaicin, a transient receptor potential vanilloid 1 (TRPV1) activator, were completely abolished by chemical deafferentation. The increased GMBF response to AITC was markedly inhibited by BIBN 4096, a calcitonin gene-related peptide receptor (CGRP) antagonist, or AGP-8412, an adrenomedullin receptor antagonist. These results suggest that AITC-stimulated TRPA1 activation results in the increased GMBF through the release of CGRP and adrenomedullin.

The rodent model of impaired gastric motility induced by allyl isothiocyanate, a pungent ingredient of wasabi, to evaluate therapeutic agents for functional dyspepsia.

Functional dyspepsia (FD) is thought to be mainly based on gastric motility dysfunction and chronic hypersensitivity, yet FD animal models has been reported a few. We studied to establish the mouse model of impaired gastric motility induced by a pungent ingredient of wasabi allyl isothiocyanate (AITC), which is reliable to evaluate prokinetic agents. Male ddY mice were used. Gastric motility was measured by 13C-acetic acid breath test in conscious mice. AITC (80 mM) was given 60 min before the measurement of motility. Prokinetic agents including itopride (30, 100 mg/kg), mosapride (0.1-1 mg/kg), neostigmine (30 µg/kg), acotiamide (10-100 mg/kg), and daikenchuto (100-1000 mg/kg) were given 40 min before the measurement. AITC impaired gastric motility without mucosal damages, which reverted 24 h after AITC treatment. The decreased motility induced by AITC was restored by prokinetic agents such as itopride, mosapride, neostigmine, and acotiamide. In separate experiment, daikenchuto recovered the decreased motility induced by AITC, although daikenchuto had no effect on motility in normal condition. In conclusion, it is considered that the AITC-induced impaired gastric motility mouse model is useful to develop new prokinetic agents for treatment of FD, and to re-evaluate traditional Japanese herbal medicines.

Role of transient receptor potential melastatin 2 in surgical inflammation and dysmotility in a mouse model of postoperative ileus.

In this study, we investigated the role of transient receptor potential melastatin 2 (TRPM2), a nonselective cation channel abundantly expressed in inflammatory cells such as macrophages, in the development of postoperative ileus, a complication of abdominal surgery characterized by gastrointestinal dysmotility. In wild-type mice, we found that intestinal manipulation, a maneuver that elicits symptoms typical of postoperative ileus, delays the transit of fluorescein-labeled dextran, promotes the infiltration of CD68+ macrophages, Ly6B.2+ neutrophils, and MPO+ cells into intestinal muscles, boosts expression of IL-1ß, IL-6, TNF-α, iNOS, and CXCL2 in intestinal muscles and peritoneal macrophages, enhances phosphorylation of ERK and p38 MAPK in intestinal muscles, and amplifies IL-1ß, IL-6, TNF-α, iNOS, and CXCL2 expression in resident and thioglycolate-elicited peritoneal macrophages following exposure to lipopolysaccharide. Remarkably, TRPM2 deficiency completely blocks or diminishes these effects. Indeed, intestinal manipulation appears to activate TRPM2 in resident muscularis macrophages and elicits release of inflammatory cytokines and chemokines, which, in turn, promote infiltration of macrophages and neutrophils into the muscle, ultimately resulting in dysmotility. NEW & NOTEWORTHY Activation of transient receptor potential melastatin 2 (TRPM2) releases inflammatory cytokines and chemokines, which, in turn, promote the infiltration of inflammatory cells and macrophages into intestinal muscles, ultimately resulting in dysmotility. Thus TRPM2 is a promising target in treating dysmotility due to postoperative ileus, a complication of abdominal surgery.

Orally active opioid µ/δ dual agonist MGM-16, a derivative of the indole alkaloid mitragynine, exhibits potent antiallodynic effect on neuropathic pain in mice.

(E)-Methyl 2-((2S,3S,7aS,12bS)-3-ethyl-7a-hydroxy-8-methoxy-1,2,3,4,6,7,7a,12b-octahydroindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate (7-hydroxymitragynine), a main active constituent of the traditional herbal medicine Mitragyna speciosa, is an indole alkaloid that is structurally different from morphine. 7-Hydroxymitragynine induces a potent antinociceptive effect on mouse acute pain through µ-opioid receptors. In this study, we developed dual-acting µ- and δ-opioid agonists MGM-15 and MGM-16 from 7-hydroxymitragynine for the treatment of acute and chronic pain. MGM-16 showed a higher potency than that of 7-hydroxymitragynine and MGM-15 in in vitro and in vivo assays. MGM-16 exhibited a high affinity for µ- and δ-opioid receptors, with K(i) values of 2.1 and 7.0 nM, respectively. MGM-16 showed µ- and δ-opioid full agonistic effects in a guanosine 5'-O-(3-[(35)S]thiotriphosphate) binding assay and in a functional test using electrically elicited guinea pig ileum and mouse vas deferens contractions. Systemic administration of MGM-16 produced antinociceptive effects in a mouse acute pain model and antiallodynic effects in a chronic pain model. The antinociceptive effect of MGM-16 was approximately 240 times more potent than that of morphine in a mouse tail-flick test, and its antiallodynic effect was approximately 100 times more potent than that of gabapentin in partial sciatic nerve-ligated mice, especially with oral administration. The antinociceptive effect of MGM-16 was completely and partially blocked by the µ-selective antagonist ß-funaltrexamine hydrochloride (ß-FNA) and by the δ-selective antagonist naltrindole, respectively, in a tail-flick test. The antiallodynic effect of MGM-16 was completely blocked by ß-FNA and naltrindole in a neuropathic pain model. These findings suggest that MGM-16 could become a class of a compound with potential therapeutic utility for treating neuropathic pain.

Distribution of transient receptor potential cation channel subfamily V member 1-expressing nerve fibers in mouse esophagus.

Transient receptor potential cation channel subfamily V member 1 (TRPV1) plays a role in esophageal function. However, the distribution of TRPV1 nerve fibers in the esophagus is currently not well understood. In the present study, we investigated the distribution of TRPV1 and neurotransmitters released from TRPV1 nerve fibers in the mouse lower esophagus. Furthermore, we investigated changes in the presence of TRPV1 in the mouse model of esophagitis. Numerous TRPV1-immunoreactive nerve fibers were seen in both the submucosal layer and myenteric plexus of the lower esophagus and colocalized with calcitonin gene-related peptide (CGRP). TRPV1 colocalized with substance P in axons in the submucosal layer and myenteric plexus. TRPV1 colocalized with neuronal nitric oxide synthase in the myenteric plexus. We observed some colocalization of CGRP with the vesicular acetylcholine (ACh) transporter, packaging of ACh into synaptic vesicles after its synthesis in terminal cytoplasm, in the submucosal layer and myenteric plexus. In the esophagitis model, the number of the TRPV1 nerve fibers did not change, but their immunoreactive intensity increased compared with sham-operated mice. Inhibitory effect of exogenous capsaicin on electrically stimulated twitch contraction significantly increased in esophagitis model compared with the effect in sham-operated mice. Overall, these results suggest that TRPV1 nerve fibers projecting to both the submucosal and muscle layer of the esophagus are extrinsic spinal and vagal afferent neurons. Furthermore, TRPV1 nerve fibers contain CGRP, substance P, nitric oxide, and ACh. Therefore, acid influx-mediated TRPV1 activation may play a role in regulating esophageal relaxation.

Neutrophil recruitment is critical for 5-fluorouracil-induced diarrhea and the decrease in aquaporins in the colon.

Diarrhea is a common side effect experienced by cancer patients undergoing clinical chemotherapy, such as with 5-fluorouracil (5-FU). However, the precise mechanisms underlying 5-FU-induced diarrhea remain unclear. In the present study, we examined the role of neutrophil in 5-FU-induced diarrhea. Mice were given 5-FU (50mg/kg, i.p.) daily for 4 days. Sivelestat sodium (100 or 300 mg/kg, i.p., neutorophil elastase inhibitor) or SB225002 (3 or 9 mg/kg, i.p., CXCR2 antagonist) was administered before the administration of 5-FU. Gene expression levels of aquaporin (AQP) 4 and 8, CXCL1, CXCL2, CXCL3, neutrophil elastase (Elane) and myeloperoxidase (MPO) in the colon were examined by real-time RT-PCR. The neutrophil (Ly-6G positive cell) number in the mucosa of colon was measured by flow-cytometric analysis. Administration of 5-FU induced diarrhea and decreased the expression levels of AQP 4 and 8 in the colon. Under the present conditions, the expression levels of CXCL1, CXCL2, CXCL3, the neutrophil markers Elane and MPO, as well as Ly-6G-positive neutrophils, in the colon were significantly increased by 5-FU. Neutrophil recruitment with decreased levels of AQP 4 and 8 were dramatically inhibited by either sivelestat sodium or SB225002. Furthermore, these reagents reduced the 5-FU-induced body weight loss and diarrhea. These findings provide evidence that neutrophil recruitment and neutrophil elastase may decrease the levels of AQP 4 and 8 in the colon of mice treated with 5-FU and contribute to the pathophysiology of 5-FU-induced body weight loss and diarrhea.

Activation and inhibition of thermosensitive TRP channels by voacangine, an alkaloid present in Voacanga africana, an African tree.

Voacangine (1) is an alkaloid found in the root bark of Voacanga africana. Our previous work has suggested that 1 is a novel transient receptor potential vanilloid type 1 (TRPV1) antagonist. In this study, the agonist and antagonist activities of 1 were examined against thermosensitive TRP channels. Channel activity was evaluated mainly using TRP channel-expressing HEK cells and calcium imaging. Herein, it was shown that 1 acts as an antagonist for TRPV1 and TRPM8 but as an agonist for TRPA1 (EC50, 8 µM). The compound competitively blocked capsaicin binding to TRPV1 (IC50, 50 µM). Voacangine (1) competitively inhibited the binding of menthol to TRPM8 (IC50, 9 µM), but it showed noncompetitive inhibition against icilin (IC50, 7 µM). Moreover, the compound selectively abrogated chemical agonist-induced TRPM8 activation and did not affect cold-induced activation. Among these effects, the TRPM8 inhibition profile is unique and noteworthy, because to date no studies have reported a menthol competitive inhibitor of TRPM8 derived from a natural source. Furthermore, this is the first report of a stimulus-selective TRPM8 antagonist. Accordingly, 1 may contribute to the development of a novel class of stimulus-selective TRPM8 blockers.

Identification of Indole Alkaloid Structural Units Important for Stimulus-Selective TRPM8 Inhibition: SAR Study of Naturally Occurring Iboga Derivatives.

The iboga alkaloid voacangine (1) has been reported previously to be the first stimulus-selective TRPM8 antagonist. In the present report, a structure-activity relationship (SAR) study is described on the effects of some naturally occurring indole alkaloid analogues on TRPM8 inhibition. Dihydrocatharanthine (10) and catharanthine (11) were found to be inhibitors of TRPM8 activity, and their IC50 values were equivalent to that of BCTC, a potent and representative TRPM8 antagonist. Furthermore, it was shown that the iboga moiety is the most crucial unit for TRPM8 blockade and that its stereostructure, as found in 1 but not in 10 and 11, is essential for chemical agonist-selective TRPM8 inhibition. These findings should provide useful information for synthesizing additional stimulus-selective and TRPM8-selective blockers.

Mechanisms that underlie µ-opioid receptor agonist-induced constipation: differential involvement of µ-opioid receptor sites and responsible regions.

Reducing the side effects of pain treatment is one of the most important strategies for improving the quality of life of cancer patients. However, little is known about the mechanisms that underlie these side effects, especially constipation induced by opioid receptor agonists; i.e., do they involve naloxonazine-sensitive versus -insensitive sites or central-versus-peripheral µ-opioid receptors? The present study was designed to investigate the mechanisms of µ-opioid receptor agonist-induced constipation (i.e., the inhibition of gastrointestinal transit and colonic expulsion) that are antagonized by the peripherally restricted opioid receptor antagonist naloxone methiodide and naloxonazine in mice. Naloxonazine attenuated the fentanyl-induced inhibition of gastrointestinal transit more potently than the inhibition induced by morphine or oxycodone. Naloxone methiodide suppressed the oxycodone-induced inhibition of gastrointestinal transit more potently than the inhibition induced by morphine, indicating that µ-opioid receptor agonists induce the inhibition of gastrointestinal transit through different mechanisms. Furthermore, we found that the route of administration (intracerebroventricular, intrathecally, and/or intraperitoneally) of naloxone methiodide differentially influenced the suppressive effect on the inhibition of colorectal transit induced by morphine, oxycodone, and fentanyl. These results suggest that morphine, oxycodone, and fentanyl induce constipation through different mechanisms (naloxonazine-sensitive versus naloxonazine-insensitive sites and central versus peripheral opioid receptors), and these findings may help us to understand the characteristics of the constipation induced by each µ-opioid receptor agonist and improve the quality of life by reducing constipation in patients being treated for pain.

Increased expression of 5-HT3 and NK 1 receptors in 5-fluorouracil-induced mucositis in mouse jejunum.

BACKGROUND AND OBJECTIVE: Although 5-fluorouracil (5-FU) is a widely used as chemotherapy agent, severe mucositis develops in approximately 80% of patients. 5-FU-induced small intestinal mucositis can cause nausea and vomiting. The current study was designed to investigate peripheral alterations due to the 5-FU-induced mucositis of neuronal and non-neuronal 5-HT3 and NK1 receptor expression by immunohistochemical analysis. METHODS: 5-FU was administered by i.p. injection to C57BL/6 mice. After 4 days, segments of the jejunum were removed. The specimens were analyzed by immunohistochemistry, real-time PCR, and enzyme immunoassay. RESULTS: The numbers of 5-HT3 receptor immunopositive cells and nerve fibers in mucosa were increased by 5-FU treatment. The 5-HT3 receptor immunopositive cell bodies were found only in jejunal submucosa and myenteric plexus in the 5-FU-treated mice. The numbers of NK1 receptor cells in mucosa and immunopositive expression of NK1 receptors in deep muscular plexus were dramatically increased in 5-FU-treated mice. Real-time PCR demonstrated that 5-FU treatment significantly increased mRNA levels of 5-HT3A, 5-HT3B, and NK1 receptors. The amounts of 5-HT and substance P increased after 5-FU treatment. The 5-HT3 or NK1 receptor immunopositive cells colocalized with both 5-HT and substance P. Furthermore, 5-HT3 and NK1 receptors colocalized with CD11b. CONCLUSIONS: The 5-HT3 and NK1 immunopositive macrophages and mucosal mast cells in lamina propria release 5-HT and substance P, which in turn activate their corresponding receptors on mucosal cells in autocrine and paracrine manners. It is assumed to result in the release of 5-HT and substance P in mucosa.

Neuronal nitric oxide synthase-derived nitric oxide is involved in gastric mucosal hyperemic response to capsaicin in rats.

BACKGROUND AND AIMS: Activation of transient receptor potential vanilloid type 1 (TRPV1) by capsaicin leads to gastric hyperemic response through capsaicin-sensitive sensory nerves and nitric oxide (NO). The aim of the present study is to examine which isoform of nitric oxide synthase (NOS)/NO is involved in the hyperemic response to capsaicin in the rat stomach. METHODS: Gastric mucosal blood flow (GMBF) was measured by laser Doppler flowmetry in rats. The localizations of TRPV1 and neuronal NOS (nNOS) in the rat gastric mucosa were detected by immunohistochemical staining. RESULTS: The nNOS inhibitor N(5)-[imino(propylamino)methyl]-L-ornithine substantially reduced GMBF during capsaicin application, whereas the endothelial NOS (eNOS) inhibitor N(5)-(1-iminomethyl)-L-ornithine did not affect the effect of capsaicin during the application. The nonselective NOS inhibitor N(G)-nitro-L-arginine methyl ester apparently inhibited the capsaicin-induced GMBF, while the inducible NOS inhibitor 1400W did not affect GMBF response to capsaicin. The immunohistochemical studies revealed nerve fibers coexpressing TRPV1 and nNOS around blood vessels in the gastric submucosa. CONCLUSION: We demonstrated for the first time that nNOS/NO is involved in gastric hyperemic responses to capsaicin.

Experimental colitis alters expression of 5-HT receptors and transient receptor potential vanilloid 1 leading to visceral hypersensitivity in mice.

Abnormalities of primary afferent nerve fibers are strongly associated with the visceral hypersensitivity state in inflammatory bowel disease. Hypersensitivity of afferent fibers occurs during inflammation. Therefore, to gain an insight into the alterations to receptors and channels expressed in primary afferent neurons, the current study aimed to investigate the time-dependent dynamic changes in levels of 5-hydroxytryptamine (5-HT)(3) receptors, 5-HT(4) receptors, transient receptor potential vanilloid type 1 (TRPV1) channels, and 5-HT regulatory factors in dextran sulfate sodium (DSS)-induced colitis model mice. 5-HT signaling molecules were detected by indirect staining with specific antibodies. TRPV1-immunoreactivity was detected by staining with fluorescein-conjugated tyramide amplification. To assess nociception, visceromotor responses (VMRs) to colorectal distension were measured by electromyography of abdominal muscles. Immunohistochemical analysis and VMRs to colorectal distention were measured during induction of DSS colitis (days 4 and 7). Inflammation led to downregulation of serotonin transporter immunoreactivities with concomitant increases in 5-HT and tryptophan hydroxylase-1-positive cell numbers. TRPV1-expressing nerve fibers gradually increased during DSS treatment. Abundant nonneuronal TRPV1-immunopositive cell-like structures were observed on day 7 of DSS treatment but not on day 4. The number of 5-HT(3) receptor-expressing nerve fibers in the mucosa was increased on day 7. On the other hand, the number of 5-HT(4) receptor-expressing nerve fibers in the mucosa decreased on day 7. We made the novel observation of increased expression of neuronal/nonneuronal TRPV1 channels and 5-HT(3) receptors, and decreased expression of 5-HT(4) receptors in the mucosa in a DSS-induced colitis model. Visceral hyperalgesia was observed on day 7 but not on day 4. A TRPV1 antagonist and a 5-HT(3) receptor antagonist attenuated the visceral hyperalgesia to the control level. The alterations of 5-HT signaling via 5-HT(3) receptors and of TRPV1 channels in mucosa may contribute to the visceral hypersensitivity in colitis model mice.

Subdiaphragmatic vagotomy induces a functional change in visceral Aδ primary afferent fibers in rats.

Vagal nerves modulate not only physical homeostasis, but also pain transmission. It has been reported that subdiaphragmatic vagal dysfunction causes visceral pain. However, the functional changes in nociceptive primary afferent fibers under such visceral pain soon after subdiaphragmatic vagal dysfunction are not fully documented. The present study was designed to investigate changes in the sensitivity of primary afferent fibers in the distal colon using a Neurometer which individually stimulates C, Aδ and Aß fibers. Under stimulation with a handmade stimulus electrode in the distal colon, the current threshold in the distal colon was recorded with high reproducibility. Subdiaphragmatic vagotomy significantly decreased the current threshold of Aδ fibers in the distal colon with no change in the sensitivity of C or Aß fibers. These results suggest that vagal dysfunction at an early stage may cause, at least in part, hypersensitivity of visceral Aδ fibers.

Dual role of serotonin in the pathogenesis of indomethacin-induced small intestinal ulceration: pro-ulcerogenic action via 5-HT3 receptors and anti-ulcerogenic action via 5-HT4 receptors.

Serotonin (5-HT) exerts multiple physiological functions not only in the central and peripheral nervous systems but also in the gastrointestinal tract, and these multiple functions are accounted for by a variety of 5-HT receptor subtypes. We investigated the role of 5-HT in the pathogenesis of indomethacin-induced intestinal lesions in mice, in relation to 5-HT receptor subtypes. A single oral administration of indomethacin (10 mg/kg) provoked damage in the small intestine of mice 24 h later, and this response was prevented by pretreatment with p-chlorophenylalanine (a 5-HT synthesis inhibitor). The administration of 5-HT3 receptor antagonists, such as ondansetron and ramosetron, dose-dependently reduced the severity of the intestinal lesions, whereas a high dose of GR113808 (a 5-HT4 receptor antagonist) significantly aggravated these lesions. In contrast, NAN-190 (a 5-HT1 receptor antagonist), ketanserin (a 5-HT2 receptor antagonist), and SB269970 (a 5-HT7 receptor antagonist) had no effect on these lesions. Mosapride (a 5-HT4 receptor agonist) significantly reduced the severity of indomethacin-induced intestinal lesions, and this protective effect was totally prevented by either GR113808 or methyllycaconitine (an α7-nicotinic acetylcholine receptor antagonist). Indomethacin increased the activity of myeloperoxidase and the expression of inducible nitric oxide synthase, inflammatory cytokines, and chemokines in the small intestine; these responses were significantly attenuated by ondansetron and mosapride. These findings suggest that endogenous 5-HT exerts a dual role in the pathogenesis of indomethacin-induced intestinal lesions: pro-ulcerogenic action via 5-HT3 receptors and anti-ulcerogenic action via 5-HT4 receptors, and the latter effect via 5-HT4 receptors may be mediated by activation of α7-nicotinic acetylcholine receptors.

Dietary agonists of TRPV1 inhibit gastric acid secretion in mice.

Capsaicin and 6-gingerol, pungent components of chilli pepper and ginger, are known as dietary agonists of transient receptor potential vanilloid-1. Transient receptor potential vanilloid-1 nerve fibers are recognized to play a role in gastric mucosal integrity in rats. In the present studies, we examined the acute effects of peroral administration of capsaicin and 6-gingerol on gastric acid secretion in conscious mice. These agents were given p. o. 30 min before the pylorus was ligated. Oral administration of capsaicin (1.0-100 mg/kg) or 6-gingerol (1.5-50 mg/kg) significantly and dose-dependently inhibited basal acid secretion. Pretreatment with BCTC, a transient receptor potential vanilloid-1 antagonist, significantly reversed the reduced basal acid secretion by capsaicin or 6-gingerol. The combination of the lowest doses of capsaicin and 6-gingerol markedly inhibited basal acid secretion in conscious mice and this was also significantly reversed by BCTC. Moreover, the combination of the maximal dose of capsaicin and 6-gingerol inhibited basal acid secretion only to the level of a single administration of the maximal dose of capsaicin. These results suggest that the combination of capsaicin and 6-gingerol has an additive effect on the inhibition of gastric acid secretion through activation of transient receptor potential vanilloid-1. In separate experiments, intraduodenal administration of either capsaicin (30 mg/kg) or 6-gingerol (15 mg/kg), whose doses were observed to have a significant inhibitory effect by oral administration, tended to inhibit basal acid secretion compared with the vehicle. These results suggest that the combination of capsaicin and 6-gingerol has an additive effect on inhibition of gastric acid secretion through activation of transient receptor potential vanilloid-1, and oral administration of transient receptor potential vanilloid-1 agonists directly stimulates transient receptor potential vanilloid-1 in the gastric lumen, resulting in a potent reduction of gastric acid secretion.

Juvenile social defeat stress exposure favors in later onset of irritable bowel syndrome-like symptoms in male mice.

Irritable bowel syndrome (IBS) is the most common functional gastrointestinal disorder. Traumatic stress during adolescence increases the risk of IBS in adults. The aim of this study was to characterize the juvenile social defeat stress (SDS)-associated IBS model in mice. Juvenile mice were exposed to an aggressor mouse for 10 min once daily for 10 consecutive days. Behavioral tests, visceral sensitivity, immune responses, and fecal bacteria in the colon were evaluated in 5 weeks after SDS exposure. Social avoidance, anxiety- and depression-like behavior, and visceral hypersensitivity were observed. Juvenile SDS exposure significantly increased the number of 5-HT-containing cells and calcitonin gene-related peptide-positive neurons in the colon. The gut microbiota was largely similar between the control and juvenile SDS groups. The alterations in fecal pellet output, bead expulsion time, plasma corticosterone concentration, and colonic 5-HT content in response to restraint stress were exacerbated in the juvenile SDS group compared with the control group. The combination of juvenile SDS and restraint stress increased the noradrenaline metabolite 3-Methoxy-4-hydroxyphenylglycol (MHPG) content and MHPG/noradrenaline ratio in the amygdala when compared with restraint stress in control mice. These results suggest that juvenile SDS exposure results in later onset of IBS-like symptoms.

Localization of TRPV1 and contractile effect of capsaicin in mouse large intestine: high abundance and sensitivity in rectum and distal colon.

We investigated immunohistochemical differences in the distribution of TRPV1 channels and the contractile effects of capsaicin on smooth muscle in the mouse rectum and distal, transverse, and proximal colon. In the immunohistochemical study, TRPV1 immunoreactivity was found in the mucosa, submucosal, and muscle layers and myenteric plexus. Large numbers of TRPV1-immunoreactive axons were observed in the rectum and distal colon. In contrast, TRPV1-positive axons were sparsely distributed in the transverse and proximal colon. The density of TRPV1-immunoreactive axons in the rectum and distal colon was much higher than those in the transverse and proximal colon. Axons double labeled with TRPV1 and protein gene product (PGP) 9.5 were detected in the myenteric plexus, but PGP 9.5-immunoreactive cell bodies did not colocalize with TRPV1. In motor function studies, capsaicin induced a fast transient contraction, followed by a large long-lasting contraction in the rectum and distal colon, whereas in the transverse and proximal colon only the transient contraction was observed. The capsaicin-induced transient contraction from the proximal colon to the rectum was moderately inhibited by an NK1 or NK2 receptor antagonist. The capsaicin-induced long-lasting contraction in the rectum and distal colon was markedly inhibited by an NK2 antagonist, but not by an NK1 antagonist. The present results suggest that TRPV1 channels located on the rectum and distal colon play a major role in the motor function in the large intestine.

MGM-9 [(E)-methyl 2-(3-ethyl-7a,12a-(epoxyethanoxy)-9-fluoro-1,2,3,4,6,7,12,12b-octahydro-8-methoxyindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate], a derivative of the indole alkaloid mitragynine: a novel dual-acting mu- and kappa-opioid agonist with potent antinociceptive and weak rewarding effects in mice.

Mitragynine is a major indole alkaloid isolated from the Thai medicinal plant Mitragyna speciosa that has opium-like properties, although its chemical structure is quite different from that of morphine. We attempted to develop novel analgesics derived from mitragynine, and thus synthesized the ethylene glycol-bridged and C10-fluorinated derivative of mitragynine, MGM-9 [(E)-methyl 2-(3-ethyl-7a,12a-(epoxyethanoxy)-9-fluoro-1,2,3,4,6,7,12,12b-octahydro-8-methoxyindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate]. We hypothesized that a dual-acting mu- and kappa-opioid agonist could produce potent antinociceptive effects with fewer rewarding effects compared with mu agonists. In this study, MGM-9 exhibited high affinity for mu- and kappa-opioid receptors with Ki values of 7.3 and 18 nM, respectively. MGM-9 showed a potent opioid agonistic effect, and its effects were meditated by mu- and kappa-opioid receptor mechanisms in in vitro assays. Subcutaneous and oral administration of MGM-9 produced potent antinociceptive effects in mouse tail-flick, hot-plate, and writhing tests. When administered orally, the antinociceptive effect of MGM-9 was seven to 22 times more potent than that of morphine. The antinociceptive effects of MGM-9 were mediated by both mu- and kappa-opioid receptors. Subcutaneous administration of MGM-9 twice daily for 5 days led to antinociceptive tolerance. In the gastrointestinal transit study, MGM-9 inhibited gastrointestinal transit, but its effect was weaker than that of morphine at equi-antinociceptive doses. Furthermore, MGM-9 induced less hyperlocomotion and fewer rewarding effects than morphine. The rewarding effect of MGM-9 was blocked by a mu antagonist and enhanced by a kappa antagonist. Taken together, the results suggest that MGM-9 is a promising novel analgesic that has a stronger antinociceptive effect and weaker adverse effects than morphine.

Immunohistochemical localization of transient receptor potential vanilloid subtype 1 in the trachea of ovalbumin-sensitized Guinea pigs.

BACKGROUND: We previously found many transient receptor potential vanilloid receptor subtype 1 (TRPV1) axons in the tracheal smooth muscle and epithelium of the guinea pig airway. One report indicates that the number of TRPV1 axons is significantly increased in patients with cough variant asthma. AIM: To determine whether the distribution of TRPV1 in the airways is altered in guinea pigs with an allergic phenotype. METHODS: Ten guinea pigs were assigned to 2 groups in a double-blind study. Five animals were sensitized with ovalbumin and the other 5 underwent sham sensitization. Cryopreserved sections (30 microm) of tracheal tissues removed from each animal were stained with polyclonal serum rabbit anti-TRPV1 antibody (1:30,000) and examined by confocal microscopy. RESULTS: Axons immunoreactive to TRPV1 localized to fine axons within the epithelium and around areas of smooth muscle, were more densely stained and frequent in the ovalbumin than in the sham group. CONCLUSION: The number of TRPV1-immunoreactive axons in the trachea increases under allergic inflammatory conditions.