Relationship between abnormal complement activation in the spinal dorsal horn and neuropathologic pain in rats

Abstract

Objective To observe the change of complement 3 in dorsal horn of spinal cord and to investigate the role of ab-normal activation of complement protein in pathogenesis of NPP. Methods This study comprises two parts. In part 1, 84 healthy male Sprague-Dawley rats were divided randomly into seven groups:normal control group, sham I d group, sham 3 d group, sham 7 d group, CCI 1 d group, CCI 3 d group, CCI 7 d group (n=12). The mechanical pain threshold were measured in different time ac-cording to the group, while the mRNA and protein of Complement 3 were determined by RT-PCR, immunoturbidimetry and immuno-histochemistry. In part 2, 48 healthy male Sprague-Dawley rats were divided randomly into sham operation + saline group, CCI + saline group, CCI + CVF group(continual injection CVF group) and CCI + saline + CVF group(single injection CVF group)(n=12). Pain thresholds by mechanical stimulation were recorded at preoperation and 1, 3, 7, 14 d after operation in each group. Comple-ment 3 expression in the spinal dorsal horn was determined immunohistochemically to confirm the efficacy of CVF. The SOD activity and MDA content in the spinal cord homogenate were determined, and intracellular changes of spinal dorsal horn neurons were ob-served under electronmicroscopy. Results The expression of mRNA and protein of complement 3 in spinal dorsal horn increased at 1, 3, 7 d after CCI, but those were not shown in rats in sham operation group and normal control group. The pearson analysis demonstrated that there was an initate relation between complement 3 content and pain threshold. Hyperalgesia was obviously alleviat-ed in CCI + saline + CVF group after administration of CVF, and the threshold revived following attenuation of the role of CVF. Hy-peralgesia was not evoked after sciatic nerve ligation in CCI + CVF group. Compared with CCI + saline group, the SOl) activity in-creased sinificianfly and MDA content decreased obviously in CCI + CVF group (P<0.05). Electronmicroscopy demonstrated mito-chondrial swelling and cytomembrane breakdown of spinal dorsal horn neurons in CCI + saline group while mitochondrial swelling was mitigated in spinal dorsal horn neurons in CCI + CVF group. Conclusion Abnormal complement activation occurred in the spinal dorsal horn of rats with peripheral nerve injury induced NPP and participated in the development of hyperalgesia. Key words: Neuropathic pain; Chronic constriction injury; Hyperalgesia; Complement 3 ; Cobra venom factor