Effects of continuous peripheral nerve block by tetrodotoxin on growth associated protein-43 expression during neuropathic pain development

Abstract

Background Peripheral nerve injury may lead to neuropathic pain and cause a markedly increase expression of growth associated protein-43 (GAP-43) in the spinal cord and dorsal root ganglion, local anesthetics blocking electrical impulse propagation of nerve fibers may also affect the expression of GAP-43 in the spinal cord and dorsal root ganglion. Objective To determine the effects of continuous peripheral nerve block by tetrodotoxin before and after nerve injury on GAP-43 expression in the dorsal root ganglion during the development of neuropathic pain. Design A randomized controlled animal experiment. Settings Department of Anesthesiology, the Second Hospital of Xiamen City; Department of Anesthesiology, the Second Affiliated Hospital of Shantou University Medical College. Materials Thirty-five Sprague Dawley (SD) rats, weighing 200–250 g, were randomly divided into four groups control group ( n =5), simple sciatic nerve transection group ( n =10), peripheral nerve block before and after sciatic nerve transection groups ( n =10). All the sciatic nerve transection groups were divided into two subgroups according to the different postoperative survival periods: 3 and 7 days ( n =5) respectively. Mouse anti-GAP-43 monoclonal antibody (Sigma Co., Ltd.), supervision TM anti-mouse reagent (HRP, Changdao antibody diagnosis reagent Co., Ltd., Shanghai), and HMIAS-100 image analysis system (Qianping Image Engineering Company, Tongji Medical University) were employed in this study. Methods This experiment was carried out in the Department of Surgery and Pathological Laboratory, the Second Affiliated Hospital of Shantou University Medical College from April 2005 to April 2006. ▪The animals were anesthetized and the right sciatic nerve was exposed and transected at 1 cm distal to sciatic notch. ▪ Tetrodotoxin 10 μg/kg was injected percutaneously between the greater trochanter and the posterior superior iliac spine of right hind limb to block the sciatic nerve proximally at 1 hour before or 4 hours after nerve injury respectively, the injection was repeated in all the rats every 12 hours. ▪ At 3 or 7 days after nerve injury, immunohistochemistry and image analysis were used to evaluate the expression of GAP-43 in the dorsal root ganglions of L 5 to the transected sciatic nerve, and quantitative analysis was also performed. ▪ Statistical analysis was performed using one way analysis of variance followed by t test. Main outcome measure Expression of GAP-43 in the right dorsal root ganglions of L 5. Results All the 35 SD rats were involved in the final analysis of results. In normal rats, there were very low expressions of GAP-43 in the dorsal root ganglions. In simple sciatic nerve transection rats 3 and 7 days after sciatic nerve transection, the average absorbance value of GAP-43 immunopositive neurons were significantly different from that in normal rats ( t =8.806, 6.771, P < 0.01). Whereas 3 and 7 days after sciatic nerve transection in rats with peripheral nerve block before and after nerve injury, the average absorbance value of GAP-43 immunopositive neurons were not significantly different from that in normal rats ( P > 0.05). Conclusion Local anesthetic continuous peripheral nerve block before or after nerve injury can suppress nerve injury induced high expression of GAP-43 during the development of neuropathic pain.