The Effect Of Vagal C Fibers Pathway In Gastroesophageal Reflux Cough

Background:Gastroesophageal reflux cough(GERC)refers to a clinical syndrome characterized by cough caused by reflux of gastric acid and other gastric contents into the esophagus.It is one of the three major causes of chronic cough.The main pathophysiological feature of gastroesophageal reflux is acid reflux.The application of acid suppression therapy,especially proton pump inhibitor(PPI),can alleviate the symptom of cough in some patients,but there are still a large number of patients with persistent cough symptom even in acid-resistant treatment,which seriously affects their lives.At present,refractory chronic cough caused by gastroesophageal reflux is a clinically difficult problem,so it is necessary to study the pathogenesis of GERC further in order to treat GERC better.At present,the research on the pathogenesis of GERC mainly focuses on three points:microaspiration?esophageal-bronchial reflex and airway hyperresponsiveness.Gastroesophageal reflux and cough have no obvious time correlation,there is little support tor microaspiration.Both esophageal-bronchial reflex and airway hyperresponsiveness are associated with airway neurogenic inflammation caused by vagus-mediated reflex.Cough is mainly regulated by vagal sensory nerves innervating the bronchus and lungs.One important group of vagal afferent pathways regulating cough reflex comes from sensory fibers innervating the esophagus.Studies have shown that acid in the esophagus stimulates the lower esophagus,which can sensitize the cough reflex pathway.This sensitization may be mediated by a subset of esophageal vagal sensory nerves,which is characterized by sensitivity to harmful stimuli.It is not clear whether ASIC3 and 5-HT3R are involved in the acid-sensitive receptor of vagus nerve except TRPV1.Our previous work has shown that esophageal acid infusion can cause elevation of 5-hydroxytryptamine(5-HT)and decrease of serotonin transporter(SERT)in esophageal tissues.5-HT-vagal pathway may play a role in esophageal acid reflux-induced airway hyperresponsiveness.However,the specific signal pathway of vagal C afferent pathway in GERC is still unclear.How does acid reflux in the esophagus cause GERC caused by the neuropeptide secretion pathway via the afferent fibers of the vagus nerve C?How to activate and regulate it from the perspective of molecular mechanism?Is it possible to block GERC if a link in this signaling pathway?Objective:The aim of this study is to determine the effect of vagus nerve C afferent fibrosis in gastroesophageal reflux cough,and to analyze the effect of drugs affecting vagus nerve C afferent fibrosis on gastroesophageal reflux cough,and to prevent and treat gastroesophageal reflux cough,which may provide a new drug targetMethods:Nonnal 45 male wistar newborn rats were used,rats were randomly divided into four groups.R1 group:positive control group(hydrochloric acid perfusion group):10 newborn rats were fed to 8-week-old adult rats,and were perfused with intraesophageal acid for 2 weeks;R2 group:transient esophageal vagus nerve C afferent fibrosis type experimental group:10 newborn rats were fed to 8-week-old adult rats and received subcutaneous injection of capsaicin(50ng/kg)for 2 days and acid perfusion for 2 weeks;R3 group:Persistent esophageal vagus nerve C afferent fibrosis experimental group:15 newborn rats were received subcutaneous injection of capsaicin(50mg/kg)for 2 days after birth,and after feeding 8-week-old adult rats,they were perfused with acid for 2 weeks;R4 group:negative control group(normal saline perfusion group):10 newborn rats were fed to 8-week-old adult rats and continuously perfused with nonnal saline for 2 weeks.The changes of lung compliance and lung resistance in rats after inhalation of different concentrations of methacholine were measured to evaluate the reactivity of airway;the pathological state of esophagus,trachea and lung tissues was detected;The mRNA of HT3R,TRPV1 and ASIC3 of esophageal tissue and NK1R,NK2R,NK3R,of bronchial and lung tissues were measured by RT-PCR.Results:Establishment of animal models and determination of airway responsiveness.Bronchial provocation test was performed with methacholine.When Mch concentration increased to 0.25 mmol/L and 0.5 mmol/L,the percentage of increased lung resistance in R1 group was significantly higher than that in group R2,R3and R4.When Mch concentration increased to 0.5 mmol/L,the percentage of decreased lung compliance in R1 group was higher than that in group R2,R3 and R4,suggesting that the airway responsiveness of rats was increased.The difference was statistically significant.Pathology:In grroup R1,the ciliary columnar epithelium in trachea tissue showed obvious hyperplasia and thickening,disordered arrangement,partial exfoliation,obvious hemorrhagic hyperemia in submucosa,obvious infiltration of inflammatory cells,thickening of distal esophageal epithelium,prolongation ot papilla,erosion and obvious infiltration of inflammatory cells in lamina propria.Inflammatory cell infiltration,visible thickening of small airway wall,airway stenosis,secretions increased.In R2 and R3 groups,tracheal ciliary columnar epithelium showed a little exfoliation and infiltration of inflammatory cells,the lower esophageal epithelium showed slight thickening,slightly prolonged nipples,and mild inflammatory cell infiltration in lamina propria.There was a slight increase in inflammatory cells in lung tissue.In R4 group the structure of trachea,lower esophagus and alveoli was clear,the classification of white blood cells was basically nonmal,and no obvious inflammatory cell infiltration and vascular congestion were observed.There was no significant difference of mRNA expression of 5-HT3R,TRPV1 and ASIC3 in esophagus and NK1R and NK2R in lung tissue among R1?R2?R3 and R4 groups.The mRNA level of NK3R in lung tissue was significantly higher in R3 group than in R1?R2?and R4 groups,the difference had reached statistically significant.Conclusion:The esophageal acid perfusion model of rat can induce esophageal mucosa histological injury,Esophageal persistent vagal degeneration can elevate the levels of NK3R in bronchial and lung tissues,and vagus nerve C afferent fibers may play an important role in gastroesophageal reflux cough.