Effect Of Inflammatory Pain And Morphine Tolerance On The Expression Of P2X₄Receptor In The Spinal Cord And Dorsal Root Ganglion In Rats

Objective:In this study, we observed the expression of P2X4receptor in the spinal cord and dorsal root ganglion(DRG) to explore the role of P2X4receptor in the development of inflammatory pain caused by formalin and acute morphine tolerance.Methods:35male Sprague-Daw ley rats were randomly divided into4groups:inflammatory group(group F,n=20)、inflammatory and morphine group(group FM,n=5)、morphine group(group M,n=5) and saline group(group NS,n=5).Group F were injected the left hind paws subcutaneously with4%formalin50ul to establish the model of inflammatory pain and were divided into4groups(Group F4d、Group F7d、Group F10d、Group F14d) according to the execution time(4、7、10、14days after the injection of formalin). Group FM were intrathecally administered morphine lOug/lOul every2hours for6times at the7th day of establishing the model of inflammatory pain, and were executed2hours after the last administration. Group M and Group NS were intrathecally administered morphine or saline lOug/10ul every2hours for6times and were executed2hours after the last administration. Paw withdrawal latency (PWL) of the left hind paws were examined to evaluate the behavior. Immunohistochemistry was used to detect the expression of P2X4receptor in the spinal cord and dorsal root ganglion.Results:1.The expression of P2X4receptor in Group F was increased in the4th day after inflammatory, and reached the peak at the7th day, then gradually declined at the10th day and14th day.2. The increased expression of P2X4receptor was observed in Group M compared with it in Group NS.3. Morphine tolerance was formed in Group M and Group FM after administering drugs at the last time. Compared with Group M, It was easier to induce morphine tolerance in Group FM.Conclusion:P2X4receptor may participate in the formation of acute morphine tolerance and inflammatory pain.