Neonatal Colonic Inflammation Regulates ?2 Adrenergic Receptor Activity In Spinal Dorsal Horn Of Adult Rats With Visceral Hypersensitivity

Objective:Irritable bowel syndrome(IBS)is a common gastrointestinal disorder characterized by chronic visceral pain in association with altered bowel habits.The ? adrenergic receptors is a member of the G protein coupling receptor family and participates in the pain signal transduction.Recent studies have indicated that ?2 adrenergic receptors played an important role in chronic pancreatitic hyperalgesia via increased expression.And ?2 adrenergic receptors can regulate the excitability of the DRG neurons by regulating the expression of the P2 X receptors through the PKA pathway.However,the precise mechanism of ?2 adrenergic receptors in the spinal cord is still poorly understood.This study was designed to investigate the role of ?2 adrenergic receptors in the spinal dorsal horn in a rat model of chronic visceral hyperalgesia induced by neonatal colonic inflammation(NCI).Methods:1.Ten-day-old pups were received an infusion of 0.2 m L of 0.5% acetic acid(AA)solution in saline into the colon 2 cm from the anus.Distension threshold to grade colorectal distention in adult male rats was recorded as a measure of visceral hypersensitivity.2.Western blotting technique and reverse transcription-PCR(RT-PCR)experiments were used to detect the expression of adrenergic receptors.3.Intrathecal injection of Butoxamine(?2 adrenergic receptor antagonist)was performed to detect the role of ?2 adrenergic receptors in NCI-induced visceral hyperalgesia.4.Fluorescence in situ hybridization(FISH)and immunofluorescence staining were applied to determine the cellular distribution of ?2 adrenergic receptors.5.The synaptic transmission of neurons in the substantia gelatinosa(SG)of spinal cord was recorded by patch clamping techniques.6.The changes of norepinephrine concentration in plasma of rats 2 weeks,4 weeks and 6 weeks were detected by ELISA.Results:1.NCI significantly upregulated the expression of ?2 adrenergic receptors in colon-related spinal cord horn at T13-L2 segments of SD rats at the age of 6 weeks.2.Compared with control group,the expression of ?1-ARs and ?3-ARs in T13-L2 segment of NCI rats was not significantly altered.3.Intrathecal injection of Butoxamine significantly reversed colorectal distention threshold of NCI rats.4.Application of Butoxamine suppressed the synaptic transmission in SG neurons of spinal cord horn in NCI rats.5.There was no significant change in norepinephrine concentration in the plasma of NCI rats at 2 weeks,4 weeks and 6 weeks.6.After incubated with NE,the amplitude and frequency of s EPSCs in control rat spinal cord horn was not significantly changed.7.After incubated with NE,the frequency of s EPSCs in NCI rat spinal cord increased significantly,and the amplitude was not markedly changed.Conclusion:These results suggest that upregulation of ?2 adrenergic receptors contributes to NCI-induced visceral hypersensitivity through increasing synaptic transmission in SG neurons of spinal cord horn.This finding and future investigation would provide a novel therapeutic strategy for chronic visceral pain in IBS patients.