The Analgesic Effects Of The Electroacupuncture Or Dexmedetomidine On Burned Rats

Objective: To explore the analgesic effects and its relevant analgesic mechanisms ofstimulation on peripheral meridians by electroacupuncture (EA) or intraperitoneal injectionof dexmedetomidine (DEX) on second-degree burned rats.Methods: The study included two parts of research contents:(1) The analgesic effects andthe primary mechanisms of EA on burned rats.(2) The analgesic effects and the primarymechanisms of intraperitoneal injection of DEX on burned rats. Experiment Ⅰ:60male Sprague Dawley(SD）rats were randomly divided into5groups: normal, sham-burned,burned, burned+EA and burned+sham-EA groups (n=12rats in each group). Rats burnedmodel established and EA treatment was given. To observe the pain behavior changes ofeach group on pre-and post-burn injury. Electric Von Fray fibre tested the mechanicalwithdrawal threshold on12,24,36,48,60and72hours post-injury; Using theimmunohistochemical method to detect the glia fibrillary acidic protein (GFAP) expressionin the PAG. Experiment Ⅱ:60male Sprague Dawley(SD）rats were randomly divided into5groups: normal, sham-burned, burned, burned+DEX1and burned+DEX2groups(n=12ratsin each group). Rats burned model established and intraperitoneal injection of DEX. Toobserve the pain behavior changes of each group pre-and post-burn injury. Electric VonFray fibre tested the mechanical withdrawal threshold on12,24,36,48,60and72hourspost-injury; Using the immunohistochemical method to detect the P2X3receptor proteinexpression in the PAG.Results: Experiment Ⅰ: In sham-burned group, the mechanical withdrawal thresholdwas insignificant compared with the normal group after burn injury（P＞0.05）; On12hrsafter burn injury, the mechanical withdrawal threshold obviously decreased on the rats ofburn, burn+EA, burned+sham-EA groups with an upregulation of GFAP expression in thePAG compared with the normal group, differences were statistically significant (all P<0.001)48hours after burns, the mechanical withdrawal threshold dropped to the lowest point andthen rebounded but compared with the control group, there was still a significantly differentexisted（P﹤0.001）；Compared with burn group, the mechanical withdrawal thresholdincreased and GFAP expression was up-regulated in the PAG in burn+EA group（P﹤0.001）.There was no statistically significant between the burn group and the burned+sham-EAgroup on the mechanical withdrawal threshold and the GFAP expression level in the PAG（P＞0.05）. Experiment Ⅱ: In sham-burned group, the mechanical withdrawal threshold wasinsignificant compared with the normal group after burn injury（P＞0．05）;12hrs after burninjury, the mechanical withdrawal threshold obviously decreased on the burned,burned+DEX1and burned+DEX2groups. Compared with the normal group, difference wasstatistically significant (P<0.001) with an upregulation of P2X3receptors expression in the PAG;48hours after burns, the mechanical withdrawal threshold dropped to the lowest pointand then rebounded, but compared with the control group, there was still significantlydifferent（P﹤0.001）；In burned rats, the MWT decreased with an up-regulation of theexpression of P2X3receptors in PAG compared with the normal and sham-burned ratsgroups (all P <0.001). The intraperitoneal injection of DEX induced an even higher increaseof P2X3receptors expression in PAG (P<0.001v.s burn group) and increased MWT valuesin burned rats (P <0.001). The various doses of DEX (5μg and10μg) led no statisticaldifferent in P2X3receptor expression and MWT values betweent the two DEXadministration groups.Conclusion: The EA treatment or injection of DEX into enterocoelia can increase themechanical withdrawal threshold on burned rats, promote the activation of astrocyte or P2X3receptor in PAG thereafter strengthen the effects of the endogenous pain control system andproduce analgesic effect on the burned rats.