HUMAN VISCERAL AFFERENT RECORDINGS: A PRE-CLINICAL HUMAN MODEL OF VISCERAL PAIN.
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Aim: We have recently developed electrophysiological recordings of human visceral afferent (HVA) activity in isolated gastrointestinal tissues. The aim of the this study was 1) test the mechano- and chemosensitivity of HVAs, 2) characterise subpopulations of HVAs based on their response to mechanical stimuli, 3) test the effect of drugs that have/are in clinical trials on the mechanosensitivity (von Frey hair (VFH) probing and appendix distension) of HVAs. Methods: All experiments were performed in accordance with UK human ethics regulations [NREC09/H0704/2]. Surgically resected human ileum, colon, and appendix were obtained from consenting patients undergoing bowel resection. Tissues were pinned in a tissue bath, or cannulated (appendix), and superfused with carbongenated Krebs buffer, at 6ml/min, 32-34°C. Mesenteric nerve bundles were carefully dissected and afferent activity was recorded using suction electrodes. Tissues were tested for mechanosensitivity (VFHs, stretching, mucosal stroking, distension) and chemosensitivity (bradykinin (BK), ATP (adenosine trisphosphate), PGE2 (prostaglandin E2), serotonin (aka 5-hydroxytryptamine (5-HT)), histamine, adenosine). The receptors involved in the activation of HVAs by BK, or ATP were also investigated. The response of HVAs to VFH probing or distension was tested before and after the application of tegaserod, STa endotoxin, or a transient receptor potential vanilloid 4 (TRPV4) agonist (GSK1016790A) or antagonist (HC067047). Results and Conclusion: HVAs were characterised as mesenteric, serosal, muscular, or muscular-mucosal. HVAs were chemosensitive to all mediators. Bradykinin B2 receptors are the most important receptors involved in the activation of HVAs by BK. P2Y receptors may play an important role in the activation of HVAs by ATP. Application of tegaserod, HC067047 or STa endotoxin reduced the HVA response to mechanical stimuli. HVA recordings are feasible and practical and are suitable for both basic scientific mechanistic studies, and could potentially be used as a pre-clinical model, in conjunction with animal experiments, to help predict the efficacy of novel compounds before clinical trials.
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