| Objective: To study the role of TNFαand c-fos expression in the spinal dorsal horn in the occurrence and maintance of spontaneous pain and the effect of minocycline on the occurrence of spontaneous pain.Methods:A total of 54 male Sprague-Dawley rats were randomly divided into P, C, and S group (n=18). mSNA (modified spinal never ligation) rats in group P(pretreatment group) were gavaged with minocycline (3 mg/100g) through mouth one hour before mSNA rats perparation. And the mSNA rats were prepared by tight light ligation with silk followed by transection of the right L5 spinal nerve and by loose ligation with a chromic gut suture(4.0) of the ipsilateral L4 spinal nerve. mSNA rats in group C(control group) were gavaged with equivalent saline through mouth one hour before mSNA rats perparation . The rats in group S ( sham group) were gavaged with equivalent saline through mouth one hour before animal prepreparation,with their right L4,L5 spinal nerve exposed but not ligated. According to different observation time, the rats in each group were randomly subdivided into three groups: the1st,4th,7th days postoperative subgroups (n=6). Observed the SFL behavior and caculated duration of SFL( s/10min). All rats were perfused to death. Then L4-5 spinal cords were dissected for pathological changes observation in the HE staining method as well as c-fos and TNFαexpression in spinal dorsal horn in the immunohistochemical staining method. Results: (1) The ratios of rats expressing SFL behavior in groupC were higher than that in groupP and groupS (p<0.001 respectively), but the ratios were no difference between groupP and groupS (p=0.50,two-tail). And the cumulative duration increased to the peak on the 4th postoperative day and sustained at this high level until 7th post-surgery in groupC. (2) Nuclear chromatin condensation or fragmentation, cell shrinkage were observed in the spinal dorsal horn of groupC rats . The pathological changes in group P rats' spinal doral horn were simlar to that in groupC, but their extent were less than that of groupC. And there were not obvious pathological changes in groupS rats' spinal doral horn. (3) TNFαexpression in the spinal dorsal horn of groupC rats was higher than that of group P rats and group S rats(p<0.01 respectively). But there were no difference between that of group P rats and group S rats(p=0.430). TNFαexpression in the spinal dorsal horn of groupC rats that reached the peak on the 4th day postoperative, then decreased subsequently, and there were no difference on the 7th day postoperative compared to the 1st day postoperative (p>0.05), but the expression on the 7th postoperative day was still higher than that in the groupP and group S(p<0.05 respectively). (4) c-fos expression in the spinal dorsal horn of groupC rats was higher than that of group P rats and group S rats(p<0.05 respectively). But there was no difference between that of group P rats and group S rats. c-fos expression in the spinal dorsal horn decreased after operation in all groups. While that in groupC was higher than that in groupP and groupS on the 1st, 4th days postoperative respectively (p<0.05 respectively), but no differenceon the 7th day postoperative(p=0.113).Conclusions: (1) mSNA rats can express the behavior of spontaneous pain strongly. (2) TNF-αis a trigger but not an maintenance of spontaneous pain. (3) c-fos is not a neural marker of the spontaneous pain. But the great c-fos expression may participate in the occurrence of spontaneous pain. (4) minocycline can suppress the occurrence of spontaneous pain, whose reason may relate to suppressing the expression of c-fos and TNF-α. |
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