Suppression of inflammatory pain by microinjecting 7-nitroindazole into dorsal root ganglion

Objective:To observe the phenomenon of complete Freund's adjuvant(CFA)-induced inflammatory pain and explore the analgesic effect of 7-nitroindazole(7-NI) on dorsal root ganglion(DRG),and briefly discuss its analgesic mechanism.Methods:Ten microliters of CFA were injected into the plantar surface of the hind paw of the mice to produce inflammatory pain models,von Frey filaments were used to determine 50% paw withdrawal threshold(PWT) adopting by up-and-down method which can be regarded as an evaluation criteria for the pain behavior test.The changes of 50% PWT were tested by microinjecting 10 μg 7-NI into DRG of the mice.Detect the expression of calcitonin gene related peptide(CGRP) in CFA-induced,7-NI treated and neuronal nitric oxide synthase(nNOS) knock-out models by Western blot.Results: Compared with DMSO group,50% PWT significantly increased in 7-NI group during 2～12 h after CFA inducing.The expression of CGRP increased after CFA injection,this effect could be reversed by 7-NI administration or nNOS knock-out.Conclusion: Microinjection of 7-NI into DRG could produce analgesia in inflammatory pain mice.Increased expression of CGRP might be the downstream mechanism resulted from NO mediated nociceptive effect in dorsal root ganglion.