Effects Of Distance And Acupoint Electro - Acupuncture On P38MAPK / CAMP Signaling Pathway In Spinal Cord Of Rats With Nucleus Pulposus

OBJECTIVETo research the effects and mechanisms of electro-acupuncture(EA) on different acupoints combinations in a rat model of neuropathic pain established successful by autologus nucleus polposus (NP). After the rat model was finished, we explored the effects of EA of different acupoint combinations (proximal+distal acupoints, proximal acupoints, distal acupoints) on pain-related behaviors. The expression of p38 mitogen-activated protein kinase (p38MAPK) and cyclic adenosine monophosphate (cAMP) in spinal cord were detected by relative technique.METHODSSeventy-eight male SD rats were divided into normal, model, sham operation, distal-proximal acupoints (DPA) group, proximal acupoints (PA) group and distal acupoints (DA) groups randomly. We established the NP rat model. Rats were needled at bilateral L5 Ex-B2, BL25, BL40 and BL60 in DPA group. Rats were needled at bilateral L5 Ex-B2 and BL25 in PA group. Rats were needled at bilateral BL40 and BL60 in DA group. They were treated for 20 minutes, once daily for 7 days. Mechanical withdrawal threshold (MWT) was measured 1 day preoperatively and at 3,5 and 7 days postoperatively. The expression of p38MAPK in spinal cord was detected by immunohistochemistry and western blot. The content of cAMP in Spinal cord was measured by enzyme-linked immunosorbent assay (ELISA) after a 7-day treatment.RESULTSBehavioral resultsThe rats in model and sham group had obvious hyperpathia after 3 days postperatively, compared with normal group (P<0.01). MWT of the rats in sham and EA groups are higher than that of the rats in model group (P<0.01). MWT in DA group is lower than that in DPA group (P<0.01, P<0.05). MWT in DA group is lower than that in PA group at 5,7 postoperatively(P<0.05). The effect of DPA is similar with that of PA. It is better than that of DA.Effects of EA on p38MAPK in the spinal cord Pathological changes of p38MAPK in spinal cord were evaluated by immunohistochemical stain at 7 days postoperatively. Immunohistochemical staining had shown that p38MAPK positive cells in spinal cord grey of model group increased. The cell body enlarged and cytoplasm color was tan hyperchromatic. These cells were situated mainly at Ⅱ-Ⅲ layer in spinal cord grey. Compared with normal group, the expression of p38MAPK in model group increased (P<0.01). The average optical density (AOD) of p38MAPK is higher in sham group(P<0.01). Compared with the model group, the expression of p38MAPK in sham and EA groups is lower (P<0.01). Compared with the PA group, the expression of p38MAPK in DA groups increased(P<0.05). There was no significant differentce between DPA and PA group. The effect of DPA is similar with that of PA. It is better than that of DA. The Western blot result showed that there was an increase of p38MAPK expression level in the spinal cord of rats in the model group, compared with normal group (P<0.01). Compared with sham group, the expression of p38MAPK in model group increased significantly (P<0.05). EA treatment reversed this increase in p38MAPK expression level in the spinal cord in model group. Compared with model group, the expression of p38MAPK in EA group reduced significantly (P<0.05,0.01). There were no significant differences among the EA groups. However, the trend of DPA and PA group were more obvious than that in DA group.Effects of EA on cAMP in the spinal cordExpression of cAMP was quantified by ELISA. Compared with normal group, the expression of cAMP in model group increased (P<0.05). Compared with the model group, the expression of cAMP in sham and EA groups is lower(P<0.05,0.01). There was no significant difference among EA groups. The effect of DPA is similar with that of PA. It is better than that of DA.CONCLUSIONStimulation of autologus nucleus pulposus could induce neuropathic pain. The surgery of autologus nucleus pulposus relocation could increase the expression levels of p38MAPK anc cAMP in the spinal cord, trigger mechanical hyperalgesia. EA at "proximal distal acupoints", "proximal acupoints" and "distal acupoints" could reverse the up-regulation of p38MAPK and cAMP expression level in spinal cord and alleviate low back pain. It might be the mechanism of EA analgesia. There are not significant differences among proximal distal, proximal and distal groups. The effect of DPA and PA is better than that of DA.