Effect Of Intrathecal Dexmedetomidine On Pain Threshold In Rats With Neuropathic Pain

Objective: To observe the effect of dexmedetomidine,whose intrathecal injection on neuropathic pain of sciatic nerve compression model of pain threshold of rats,and the activation level of P38 MAPK and the protein level of P38 mRNA,so as to explore the mechanism of analgesic effect of dexmedetomidine on neuropathic pain.Methods: 72 male SD rats,weight 225 g to 275 g,according to the random digital table method,divided into normal control(sham operation)group,chronnic constriction injure model(CCI)group and dexmedetomidine(DEX+CCI)group.The first group only cut the muscle layer,blunt separation of sciatic nerve without any treatment.The other two groups,the sciatic nerve was ligated to establish the chronnic constriction injure rat model,and the sheath built in tube model was established.Dexmedetomidine group received intrathecal dexmedetomidine 2 ?g/kg for 14 d after sciatic nerve compression injury,and the same amount of normal saline was injected into chronnic constriction injure model group.The incubation period and the incubation period of the contraction foot were measured in three groups of rats.The expression of P38 MAPK in spinal dorsal root ganglion was detected by immunohistochemistry.The expression level of P38 MAPK mRNA in spinal dorsal root ganglion neurons was detected by reverse transcription polymerase chain reaction(RT-PCR).Results: If the rats whose sciatic nerve branch treated with ligature had a pain response after the anesthetic was awake,it was shown that the model was successful.After the intrathecal administration,it was found that the pain in the DEX+CCI group was significantly reduced from the third day after the operation,compared with the CCI group.After measuring the latent period of heat shrinkable foot and the latency of mechanical shrinkage,it was found that the thermal pain threshold and mechanical pain threshold of group CCI and group DEX+CCI were significantly lower than those of control group(P<0.05).However,compared with the CCI group,the postoperative heat pain threshold and mechanical pain threshold in group DEX+CCI were significantly higher(P<0.05).Meanwhile,compared with the control group,the results of immunohistochemistry and RT-PCR showed that the expression of P38 and mRNA protein in CCI group and DEX+CCI group increased significantly after operation(P<0.05).Compared with the CCI group,the immuno histochemical reaction of P38 and the protein expression level of mRNA were significantly lower in group DEX+CCI after operation(P<0.05).Conclusion: Dexmedetomidine intrathecal injection can improve the thermal pain threshold and mechanical pain threshold in a rat model of neuropathic pain,and its mechanism may be related to the inhibition of P38 MAPK activation and the downregulation of P38 mRNA protein expression.