Mo1860 Identification of Kappa Opioid Receptors on Colonic Sensory Nerves and Their Up-Regulation in a Mouse Model of Chronic Visceral Hypersensitivity

Abstract

Background: Inflammatory bowel disease (IBD) is characterized by chronic inflammation of the gastrointestinal tract. This relapsing condition is often associated with debilitating abdominal pain, which in some cases can persist throughout quiescent stages of the disease. The regulatory mechanisms involved in central sensitization and peripheral neuroplasticity in the context of IBD-related visceral pain remains elusive. A growing body of evidence suggests a role for the transient receptor potential vanilloid 1 (TRPV1) in visceral hypersensitivity. TRPV1 is expressed in sensory dorsal root ganglion (DRG) neurons and is directly involved in nociception. Previous studies have demonstrated that TRPV1-deficient mice experience reduced thermal hyperalgesia during inflammation, thus suggesting a role for TRPV1 in inflammatory pain. The objective of the present study was therefore to investigate the role of TRPV1 in visceral pain in the dextran sulfate sodium (DSS) murine model of colitis. Methods: Mice were given DSS in drinking water for 7 days, after which spontaneous visceral pain was assessed using the non-invasive, animal behavior recognition system LABORAS. Control and DSS-treated mice were then sacrificed and colon-innervating DRGs collected for quantitative PCR, immunostaining, and neuronal dissociation. In Vitro studies were performed with human neuroblastoma NG108 cells. Results: DSS-treated mice showed reduced mobility and frequency of grooming and climbing, which likely reflect spontaneous visceral pain. Remarkably, while controls cells showed very few processes, dissociated DRG neurons isolated from DSS-treated mice displayed extensive neurite outgrowth after 24 h in culture. Immunocytochemistry later revealed TRPV1 expression along the entire length of these axons. These results are supported by In Vitro data demonstrating that exposure to a mixture of proinflammatory cytokines (bradykinin, histamine, and serotonin) induces neurite outgrowth and TRPV1 membrane trafficking in TRPV1-transfected neuronal NG108 cells. Finally, PCR analysis demonstrated that the neuronal morphological changes observed in DSS-treated animals were associated with a significant decrease in the expression of the small Rho GTPase RhoA and Rho kinase, both of which are known to modulate neurite outgrowth. Conclusion: These results demonstrate that DSS-colitis induces changes in neuronal morphology and modulation of TRPV1 trafficking, which may play a role in visceral hypersensitivity in the context of gastrointestinal inflammatory disorders. Current experiments using pharmacological inhibitors of the RhoA/Rho kinase signaling axis and TRPV1deficient animals will provide important insights into the exact role of TRPV1 in IBD-related visceral hypersensitivity and perhaps identify new targets for the treatment of chronic pain in these patients.