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Patients with cholestatic disease exhibit pruritus and analgesia, but the mechanisms underlying these symptoms are unknown. We report that bile acids, which are elevated in the circulation and tissues during cholestasis, cause itch and analgesia by activating the GPCR TGR5. TGR5 was detected in peptidergic neurons of mouse dorsal root ganglia and spinal cord that transmit itch and pain, and in dermal macrophages that contain opioids. Bile acids and a TGR5-selective agonist induced hyperexcitability of dorsal root ganglia neurons and stimulated the release of the itch and analgesia transmitters gastrin-releasing peptide and leucine-enkephalin. Intradermal injection of bile acids and a TGR5-selective agonist stimulated scratching behavior by gastrin-releasing peptide- and opioid-dependent mechanisms in mice. Scratching was attenuated in Tgr5-KO mice but exacerbated in Tgr5-Tg mice (overexpressing mouse TGR5), which exhibited spontaneous pruritus. Intraplantar and intrathecal injection of bile acids caused analgesia to mechanical stimulation of the paw by an opioid-dependent mechanism. Both peripheral and central mechanisms of analgesia were absent from Tgr5-KO mice. Thus, bile acids activate TGR5 on sensory nerves, stimulating the release of neuropeptides in the spinal cord that transmit itch and analgesia. These mechanisms could contribute to pruritus and painless jaundice that occur during cholestatic liver diseases.

Background: Using data from the Rome Foundation Global Epidemiology Study examining prevalence of disorders of gut–brain interaction (DGBI) in 33 countries, this study explored the prevalence of all 22 disorders in Canada. It examined differences related to geography and sociodemographic factors, health impact and compared these findings to other countries. Methods: The Rome Foundation survey was conducted through the Internet, targeting 2000 Canadian participants. The survey used the validated ROME IV diagnostic questionnaire to identify the 22 DGBI and an in‐depth supplemental questionnaire that included quality assurance techniques. Key Results: There were 2029 respondents with a mean age of 48 years and 50% females. Diagnostic criteria for at least one of the 22 DGBI were met by 41.3%, similar to other countries. Functional constipation, functional diarrhea, and unspecified functional bowel disorders were most common. Irritable bowel syndrome prevalence was 4.2% using Rome IV and 10.1% using ROME III criteria. DGBI were associated with poorer quality of life and increased psychological symptom scores. Prevalence of DGBI ranged from 48% in Quebec to 36% in British Columbia. Prescription pain medication was reported by 17% with DGBI compared to 9% without DGBI and correlated negatively with mental health and physical well‐being. Quebecers and francophones were in limited number but reported higher DGBI prevalence and symptom severity compared to others. Conclusions & Inferences: A large proportion of Canadians suffer from DGBI which seriously impact their well‐being. Findings highlight the need for further research and education, including understanding whether significant regional and cultural differences contribute to DGBI. [ABSTRACT FROM AUTHOR]

While effective in treating abdominal pain, opioids have significant side effects. Recent legalization of cannabis will likely promote use of cannabinoids as an adjunct or alternative to opioids, despite a lack of evidence. We aimed to investigate whether cannabinoids inhibit mouse colonic nociception, alone or in combination with opioids at low doses. Experiments were performed on C57BL/6 male and female mice. Visceral nociception was evaluated by measuring visceromotor responses (VMR), afferent nerve mechanosensitivity in flat-sheet colon preparations, and excitability of isolated DRG neurons. Blood oxygen saturation, locomotion, and defecation were measured to evaluate side effects. An agonist of cannabinoid 1 receptor (CB1R), arachidonyl-29-chloroethylamide (ACEA), dose-dependently decreased VMR. ACEA and HU-210 (another CB1R agonist) also attenuated colonic afferent nerve mechanosensitivity. Additionally, HU-210 concentration-dependently decreased DRG neuron excitability, which was reversed by the CB1R antagonist AM-251. Conversely, cannabinoid 2 receptor (CB2R) agonists did not attenuate VMR, afferent nerve mechanosensitivity, or DRG neuron excitability. Combination of subanalgesic doses of CB1R and m-opioid receptor agonists decreased VMR; importantly, this analgesic effect was preserved after 6 d of twice daily treatment. This combination also attenuated afferent nerve mechanosensitivity and DRG neuron excitability, which was inhibited by neuronal nitric oxide synthase and guanylate cyclase inhibitors. This combination avoided side effects (decreased oxygen saturation and colonic transit) caused by analgesic dose of morphine. Activation of CB1R, but not CB2R, decreased colonic nociception both alone and in synergy with m-opioid receptor. Thus, CB1R agonists may enable opioid dose reduction and avoid opioid-related side effects. [ABSTRACT FROM AUTHOR]

Capsaicin-sensitive extrinsic sensory nerves and submucosal vasodilator neurons provide important vasodilator input to submucosal arterioles, but relatively little is known about the signaling between these populations and the sympathetic vasoconstrictor innervation. This study examined whether release of sympathetic purines can modulate dilator nerves. In vitro submucosal preparations from guinea pig ileum were modified to leave the parent mesenteric artery intact so that perivascular sympathetic and extrinsic afferent nerves could be activated by a bipolar stimulating electrode placed on the parent artery, and submucosal vasodilator neurons were activated using focal electrodes placed on submucosal ganglia. The outside diameter of submucosal arterioles was monitored using videomicroscopy, and dilator responses were examined after preconstricting vessels 80-95% with prostaglandin [F.sub.2[alpha]] (400 nM). Mesenteric nerve stimulation evoked a frequency-dependent dilation, with suramin (100 [micro]M) present throughout to inhibit P2x receptor-mediated vasoconstrictions. In the presence of guanethidine (10 [micro]M) to inhibit sympathetic purine release, superfusion of ATP (200 nM-6 [micro]M) caused a concentration-dependent inhibition of nerve-evoked dilations. Vasodilations to substance P (10 nM) were not inhibited by ATP in the presence of guanethidine, implicating a presynaptic effect of ATP on neurotransmitter release. The inhibitory effect of ATP was blocked by the adenosine receptor antagonist 8-phenyltheophylline (8-PT; 10 [micro]M). In addition, 8-PT increased the amplitude of nerve-evoked dilations, suggesting a tonic inhibitory effect of adenosine receptors on vasodilator release. Dilations evoked by electrical stimulation of submucosal ganglia were also inhibited almost 50% by ATP (2 [micro]M) and its nonhydrolyzable analog, [alpha],[beta]-methylene-ATP (10 [micro]M). These data suggest that sympathetic varicosities release ATP or a related purine that can act at presynaptic adenosine receptors on extrinsic sensory and submucosal vasodilator neurons to inhibit neurotransmitter release. purinergic neurotransmission; vasodilation; extrinsic afferent neuron; substance P doi: 10.1152/ajpgi.00291.2009.

Two TTX-resistant [Na.sup.+] currents in mouse colonic dorsal root ganglia neurons and their role in colitis-induced hyperexcitability. Am J Physiol Gastrointest Liver Physiol 287: G845-G855, 2004. First published June 17, 2004; 10.1152/ajpgi.00154.2004.--The composition of [Na.sup.+] currents in dorsal root ganglia (DRG) neurons depends on their neuronal phenotype and innervation target. Two TTX-resistant (TTX-R) [Na.sup.+] currents [voltage-gated Na channels ([Na.sub.v])] have been described in small DRG neurons; one with slow inactivation kinetics ([Na.sub.v]1.8) and the other with persistent kinetics ([Na.sub.v]1.9), and their modulation has been implicated in inflammatory pain. This has not been studied in neurons projecting to the colon. This study examined the relative importance of these currents in inflammation-induced changes in a mouse model of inflammatory bowel disease. Colonic sensory neurons were retrogradely labeled, and colitis was induced by instillation of trinitrobenzenesulfonic acid (TNBS) into the lumen of the distal colon. Seven to ten days later, immunohistochemical properties were characterized in controls, and whole cell recordings were obtained from small ( tyrosine kinase A-positive neurons: sodium channels; nociception colon

This study examines whether intestinal inflammation leads to changes in the properties of ion channels in dorsal root ganglia (DRG) neurons. Ileitis was induced by injection of trinitrobenzene sulfonic acid (TNBS), and DRG neurons innervating the ileum were labeled using fast blue. Intracellular recording techniques were used to measure electrophysiological properties of acutely dissociated neurons 12-24 h after dissection. Nociceptive neurons were identified by sensitivity to capsaicin, tetrodotoxin resistance, and size (70% compared with controls (P < 0.001), but the resting membrane potential was unchanged. Cell diameter, input resistance (67%), and action potential upstroke velocity (22%) increased in the TNBS group (P < 0.05). The number of action potentials discharged increased in the TNBS group (P < 0.001), whereas application of 4-aminopyridine to control cells mimicked this effect. This study demonstrates that ileitis induces hyperexcitability in nociceptive DRG neurons and changes in the properties of [Na.sup.+] and [K.sup.+] channels at the soma, which persist after removal from the inflamed environment. sensory neurons; small intestine; abdominal pain; inflammation; peripheral sensitization; trinitrobenzene sulfonic acid; dorsal root ganglia

The mechanisms of action of endothelin and the maxi-potassium+ (maxi-K+) channels in the vasoconstriction of mesenteric and submucosal arteriole smooth muscle cells of the small intestine were investigated. Male albino guinea pigs were used as experimental models to determine the function of endothelin in resistance arterioles by measuring vasomotor activity in the vessels and monitoring membrane electrical properties in acutely dissociated smooth muscle cells. Results showed that opening maxi-K+ channels attenuated the impact of contraction induced by endothelin-1.

Oral squamous cell carcinoma (OSCC) is one of the most painful cancers, which interferes with orofacial function including talking and eating. We report that legumain (Lgmn) cleaves protease-activated receptor-2 (PAR2) in the acidic OSCC microenvironment to cause pain. Lgmn is a cysteine protease of late endosomes and lysosomes that can be secreted; it exhibits maximal activity in acidic environments. The role of Lgmn in PAR2-dependent cancer pain is unknown. We studied Lgmn activation in human oral cancers and oral cancer mouse models. Lgmn was activated in OSCC patient tumors, compared with matched normal oral tissue. After intraplantar, facial or lingual injection, Lgmn evoked nociception in wild-type (WT) female mice but not in female mice lacking PAR2 in NaV1.8-positive neurons (Par2Nav1.8), nor in female mice treated with a Lgmn inhibitor, LI-1. Inoculation of an OSCC cell line caused mechanical and thermal hyperalgesia that was reversed by LI-1. Par2Nav1.8 and Lgmn deletion attenuated mechanical allodynia in female mice with carcinogen-induced OSCC. Lgmn caused PAR2-dependent hyperexcitability of trigeminal neurons from WT female mice. Par2 deletion, LI-1, and inhibitors of adenylyl cyclase or protein kinase A (PKA) prevented the effects of Lgmn. Under acidified conditions, Lgmn cleaved within the extracellular N terminus of PAR2 at Asn30↓Arg31, proximal to the canonical trypsin activation site. Lgmn activated PAR2 by biased mechanisms in HEK293 cells to induce Ca2+ mobilization, cAMP formation, and PKA/protein kinase D (PKD) activation, but not β-arrestin recruitment or PAR2 endocytosis. Thus, in the acidified OSCC microenvironment, Lgmn activates PAR2 by biased mechanisms that evoke cancer pain. [ABSTRACT FROM AUTHOR]