BACKGROUND: Growth-associated protein-43 (GAP-43) expression in the nervous system has been demonstrated to promote neural regeneration, neuronal growth and development, as well as synaptic reconstruction. Neurofilament 200 (NF200) expression could reflect degree of injury and repair in injured spinal axons. OBJECTIVE: To observe NF200 expression changes in a rat model of complete spinal cord injury following GAP-43 treatment and to explore the effects of GAP-43 following spinal cord injury.DESIGN, TIME AND SETTING: A randomized, controlled, animal experiment was performed at the Laboratory of Histology and Embryology of Kunming Medical University between March 2007 and October 2008.MATERIALS: GAP-43 and GAP-43 antibody were provided by Beijing Boao Biology, China; mouse anti-rat NF200 antibody was purchased from Chemicon, USA.METHODS: Female, 8-week-old, Sprague Dawley rats were randomly assigned into three groups following complete spinal cord injury, with 20 animals in each group: GAP-43 antibody, GAP-43, and model groups. In addition, each group was subdivided into four subgroups according to sampling time after modeling, i.e., 3-, 5-, 9-, and 15-day groups, with 5 rats in each group. GAP-43 antibody or GAP-43 was injected into injury sites of the spinal cord, 5 μg/0.2 mL, respectively, twice daily for three consecutive days, followed by three additional days of injection, once daily. The model group did not receive any treatment following injury.MAIN OUTCOME MEASURES: NF200 expression in the damaged spinal area at different stages was detected by immunohistochemistry; lower limb motion function following injury was evaluated using the Basso, Beattie and Bresnahan (BBB) locomotor rating scale.RESULTS: NF200 expression was significantly reduced in the GAP-43 antibody group, compared with GAP-43 and model groups, at 3 and 5 days after spinal cord injury (P < 0.05). In addition, the model group expressed significantly less NF200 than the GAP-43 group (P < 0.05). BBB scores from the GAP-43 antibody and model groups were remarkably less than the GAP-43 group (P < 0.05). At 9 and 15 days of injury after drug withdrawal, NF200 expression was increased in the GAP-43 antibody group, and NF200 expression and BBB scores in the GAP-43 antibody and GAP-43 groups were significantly greater than in the model group (P < 0.05). In particular, the GAP-43 group exhibited greater BBB scores than the GAP-43 antibody group at day 9 (P < 0.05).CONCLUSION: GAP-43 promoted NF200 expression and recovery of lower limb function. Early administration of GAP-43 antibody produced reversible nerve inhibition, which was rapidly restored following withdrawal.