Changes In Vanilloid Receptor 1 In Dorsal Root Ganglion In Rats With Imflammatory Pain-morphine Tolerance And Effects Of MAPK Signal Pathway

Clinically, a long-term therapy of opioids has been regarded as a effective method for management of chronic and cancer pain, but opioid tolerance occurs following chronic drug exposure which limits their usefulness. The exact neural plasticity mechanisim which contribute to morphine tolerance is not yet clear entirely, but studies have shown that morphine tolerance and neuropathic pain share the same cellular mechanism. Calcitonin gene-related peptide (CGRP), P substance (SP) may be involved in nociceptive mechanism of morphine tolerance. Meanwhile, more and more studies have focus on the transient receptor potential vanilloid subfamily 1(TRPV1;VR1) which is a member of nociceptors.There were many kinds of nociceptors and pain transmitters in dorsal root ganglion(DRG) which is a site for processing and integrating nociceptive information. In this study, based on the model of inflammation-morphine tolerance, we investigate the effects of TRPV1 and p-TRPV 1 in neural plasticity changes of DRG. In recent years, about MAPK signal transduction pathways for chronic pain signal transduction pathways and cell signaling molecule in research made certain progress. Therefore, in this research from the angle of plastic changes of DRG MAPK signal transduction pathways influence, the reason and mechanism of morphine tolerance will be discussed, in order to seek solution method of clinical morphine tolerance.Part One:Establishment of arthritis-chronic morphine tolerance rat model and combined with MAPK inhibitersObjective To establish the rat model of arthritis-chronic morphine tolerance and combined with MAPK inhibiters, and to investigate the effects of MAPK on the formation of morphine tolerance.Methods Forty-five adult male SD rats with successful intrathecal cannulation were randomly divided into 9 groups(n=5 each):Group A:administered 10μl normal saline intrathecally after chronic inflammation pain (CIP) in hind paw induced by complete Freund's adjuvant(CFA) two times a day for 7 consecutive days. Group B: administered 10μg/kg(10μl) morphine intrathecally two times a day for 7 consecutive days. Group C:administered 10μg/kg(10μl) morphine intrathecally after CIP in hind paw induced by CFA only once. Group D:administered 10μg/kg(10μl) morphine intrathecally after CIP in hind paw induced by CFA two times a day for 7 consecutive days. Group E:based on the methods of group A, given 10μ125%DMSO 30 min before morning NS. Group F:based on the methods of group D, given 10μ125%DMSO 30 min before morning morphine. Group G:based on the methods of group D, given 10μg PD98059 30 min before morning morphine. Group H:based on the methods of group D, given 10μg SB203580 30 min before morning morphine. Group I:based on the methods of group D, given 50μgSP600125 30 min before morning morphine.The paw withdrawal latency(PWL) to noxious thermal stimulation and the paw withdrawal threshold to mechanical stimulation was measured daily.Results Morphine tolerance occurred in group B, F, G, H and I. The level of hyperalgesia in group G, H and I is lower than that in group D.Conclusion Chronic intrathecal morphine exposure can induce morphine tolerance in arthritis rats. MAPK inhibiters can inhibit the formation of morphine tolerance.Part Two:Effects of opioids tolerance induced by intrathecal morphine on expression of TRPV1 and p-TRPV1 in dorsal root ganglion in rats with inflammation in hind paw and effects of MAPK inhibitersObjective To investigate the effects of opioids tolerance induced by intrathecal (IT) morphine on expression of TRPV1 and p-TRPV1 in dorsal root ganglion in rats with chronic inflammation pain(CIP) in hind paw and effects of MAPK inhibiters.Methods The methods for group dividing and behavioral testing was the same as part one.The lumbar segment(L4₆) of DRG was removed on the 7th day after administration for determination of TRPV1 and p-TRPV1 expression in protein of the DRG using Western blot.Results Morphine tolerance occurred in group B, F, G, H and I. Among the nine groups, the expression of TRPV1 and p-TRPV1 in group D were the highest.Conclusion The changes in expression of TRPV1 and p-TRPV1 in protein of DRG are involved in the mechanism of morphine tolerance. MAPK inhibiters can inhibit the formation of morphine tolerance, attenuated expression of TRPV1 and p-TRPV1 are involved in the mechanism of that.