A243 HISTAMINE H1-RECEPTOR ANTAGONISTS SUPPRESS THE HYPEREXCITABILITY OF NOCICEPTIVE NEURONS EXPOSED TO IBS-C PATIENT STOOL SUPERNATANTS

Abstract

Abstract Background Abdominal pain is the primary cause of morbidity in many chronic GI disorders such as IBS, but the molecular mechanisms contributing to pain signaling are unclear. Stool supernatants from patients with diarrhea-predominant IBS increase the excitability of DRG neurons compared to supernatants from healthy controls, suggesting that mediators in the stool may sensitize nociceptors. Additionally, histamine has been implicated as a mediator of hypersensitivity in IBS patients. However, it is unclear if stool supernatants from constipation-predominant IBS (IBS-C) patients affect the excitability of DRG neurons. Furthermore, it is unknown if specific neuro-mediators in stool such as histamine impact the excitability of nociceptive neurons in this subgroup of IBS patients. Aims To evaluate whether IBS-C stool supernatants induce nociceptive signaling in DRG neurons compared to healthy control (HC) stool supernatants. If so, to evaluate the role of histamine 1 (H1) receptors in DRG neuron nociceptive signaling initiated by mediators in IBS-C stool supernatants. Methods IBS-C (n=5) and HC (n=2) patient stool was collected, filtered, and dissolved with Krebs solution in a 1:8 (g/v) dilution. Dorsal root ganglion (DRG) neurons from C57BL/6 mice were incubated with HC or IBS-C stool supernatant for 30 minutes. To evaluate whether histamine in stool supernatants can sensitize H1 receptors on nociceptors, DRG neurons were pre-incubated with the H1-receptor antagonist pyrilamine (1μM, 30 min) before stool supernatants. Changes in DRG neuronal excitability were recorded using perforated patch-clamp techniques to measure the rheobase (minimum input current needed to elicit an action potential) and the resting membrane potential (RMP). Results In neurons incubated with IBS-C stool supernatants (n=28) the rheobase decreased (63%) compared to healthy controls (78 ± 13.7 pA; n=6). This effect was reversed in DRG neurons pre-incubated with the H1 receptor antagonist, pyrilamine, (n=26) (77 ± 5.9 pA, p<0.001) compared to neurons incubated with IBS-C supernatant alone (50 ± 5.13 pA; n=28). No changes were found in the RMP. The data were analyzed with the non-parametric Kruskal-Wallis test. Conclusions IBS-C stool supernatants increase the excitability of DRG neurons compared to HC. Furthermore, the H1-receptor antagonist pyrilamine inhibits the neuronal hyperexcitability evoked by mediators in IBS-C patient stool. These findings suggest that the neuroactive metabolite histamine may contribute to visceral pain experienced by patients with IBS-C. Further studies are needed to examine whether similar signaling to nociceptive neurons by stool supernatants occurs in other subtypes of IBS. Funding Agencies CAG, CIHR