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 hi the Department of Surgery and Pathological Laboratory, the Second Affiliated Hospital of Shantou University Medical College from April 2005 to April 2006.①The animals were anesthetized and the right sciatic nerve was exposed and transected at 1 cm distal to sciatic notch.②Tetrodotoxin 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.③At 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 LS to the transected sciatic nerve, and quantitative analysis was also performed.④Statistical 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 L5. 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.