898 Chronic Stress-Induced Visceral Hyperalgesia: Evidence That the Formation of CB1 and TRPV1 Receptor Complexes Modulates Pain in Dorsal Root Ganglion (DRG) Neurons

Abstract

Introduction: PGD2 is an important mediator released after mast cell activation. Our previous studies demonstrated PGD2 sensitizes esophageal nodose C-fibers to increase their response to esophageal distension. This study aims to determine the underlying mechanism of the sensitization process. Methods: PGD2 DP1 receptor expressions in nodose neurons were determined by immunofluorescent-staining, Western blot, and RT-PCR. Extracellular single fiber recordings were performed from vagal nodose neurons using ex vivo esophageal-vagal preparations with intact nerve endings in the esophagus. We recorded action potentials evoked by esophageal distensions before and after perfusion of PGD2 with/without pretreatment of DP1 receptor antagonist BWA 868C. Whole-cell patch-clamp recording was performed to investigate the action of PGD2 on isolated nodose neurons. Viscermotor responses (VMR) to esophageal distension were recorded by electromyography from acromiotrapezius muscles in animals receiving PGD2 injection (20 μl, 100 nM) into the wall of the esophagus before and after truncal vagatomy. Results: DP1 receptor expressions were identified in nodose neurons by immunofluorescent-labeling, Western blot, and RT-PCR. 98% of DP1positive neurons were of smalland medium-diameters (φ 0.05, n=4). Whole-cell patch-clamp recording from isolated nodose neurons demonstrated PGD2 (1 μM) depolarized recorded neurons (13±2 mV, n=5) accompanied by an increase in the neuronal input resistance from 360±20 to 420±25 MΩ. IV relationship studies showed current reversed at 105 mV suggesting the effect was mediated by the closure of K+ channel(s). Compared to controls, PGD2 injection into the esophagus significantly enhanced esophageal distension evoked-VMRs at distension pressures 20, 40, 60, and 80 mmHg respectively (p <0.05, n=3). Left truncal vagatomy attenuated PGD2induced enhancements of VMR in response to esophageal distension (p <0.05, n=3) indicating the participation of vagal afferent pathway in this sensitization process. Conclusion: These data demonstrate mast cell mediator PGD2 plays a crucial role in sensitization of esophageal nodose C-fiber neurons to induce esophageal mechanical hypersensitivity. This sensitization effect is mediated via DP1 receptor and involves downstream K+ channel.