| Objective:To observe the effect of sacral injection dexmedetomidine and morphine on pain behavior, thermal hyperalgesia and c-fos expression in neuropathic pain rats and explore their analgesic effect mechanism of the level of the spinal cord.Methods:Choose sixty male Wister rats (weighted from 250g to 300g), for raising adaptability 3-5 days. And then, to determine feet reflection of the thermal stimulate latency test, its determination value as a thermal stimulate the base value of pain threshold, according to the basic threshold of screening thermal stimulate response to pain sensitive or slow rats, (thermal pain threshold< 10s or> 60s). Screening qualified rats out into experiment, and were randomly choose into sham-operation group(J, n=12):the right sciatic nerve was exposed for five minutes, without ligation and normal saline 100μl was given to the rats by sacral injection; the right sciatic nerves of other rats were ligated loosely to establish neuropathic pain model. The successful model were randomly devided into four groups(n=12 each):CCI+saline control group(group S): normal saline 100μl was given by sacral injection; CCI+morphine treated group (group M):morphine (1.5μg/μl) 100μl was given by sacral injection; CCI+dexmedetomidine treated group(groupD): dexmedetomidine (0.005μg/μl) 100μl was given by sacral injection; CCI+dexmedetomidine plus morphine treated group(group DM):morphine(1.5μg/μl)+dexmedetomidine (0.00511 g/μl) mixed liquid 100μl was given by sacral injection. The drugs were given by sacral injection every day from first days in postoperative to fourteenth days. Observe the changes of behavior and thermal withdrawal latency on 1,3,5,7,10,14 post-operative days in all rats. On the fourteenth day, c-fos like immunoreactivity(FLI)cells were identified by the immunohistochemical techniques.Results:(1)There were large significant differences between group S and group J in the grade of leg motion(P<0.01); there were no significant differences between group DM and group J(P>0.05), in the fourteenth day, there were significant differences group DM compared with group D and group M(P<0.05). (2)There were significant differences between group S, D, M, DM and group J(P<0.05 or P<0.01) about thermal pain threshold in every time point. There were significant differences compared with the value of thermal pain threshold in the perioperative period (P<0.05 or P<0.01); there were large significant differences between group DM and group S(P<0.01)in the tenth day; there were significant differences group DM compared with group M and group D in the fourteenth day (P<0.05). (3) There were significant differences between groupS, D, M, DM and group J(P<0.05 or P<0.01), in the numbers of FLI cells of each lamina in the spinal dorsal horn; there were large significant differences between group S and group DM(P<0.05 or P<0.01); groupS see large short with Fos-like immunoreactive neurons, mainly inⅠ～Ⅱ,Ⅴ～Ⅵlayer each floor were significantly more than groupDM(P<0.01),group M(P<0.05) and group D(P <0.05); there were large significant differenees between group DMand group S(P<0.01), in thenumbers of FLI cellS i n each lamina of spinal dorsal horn; Fos-like immunoreactivity group DM was significantly less than the number of neurons group D(P<0.05); there were significant di rferences between group DM and group M(P<0.05), in the numbers of FLI cells in larainaeⅠ～Ⅱin spinal dorsal horn.Conclosion:The sacral nerve block by dexmedetomidine plus morphine signficantly have analgesic effect in neuropathic pain rats, dexmedetomidine-morphine combination is superrior to morphine alone for analgesic effect in neuropathic pain rats. To desease the noceiceptional response in the spinal dorsal horn may be their analgesic mechanism. |
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