An electrophysiologic model for functional assessment of effects of neurotrophic factors on facial nerve reinnervation

Objectives: To establish a sound objective model for assessing the effects of neurotrophic factors on facial nerve function after injury and to compare the effects of brain-derived neurotrophic factor (BDNF) with its neutralizing antibody on facial nerve function after injury. Design: Prospective electrophysiologic analysis of recovery of function 4 weeks after axotomy involving facial nerve transection and primary end-to-end reanastomosis in adult rats and blind comparison with randomized intramuscular injection of either BDNF, monoclonal antibody to BDNF in neutralizing concentration, or control solution. Results: There were no statistically significant differences between groups in latencies, duration, amplitude, area, or conduction velocity before axotomy, and recorded conduction velocities were consistent with previously reported values, which suggests that the recordings were reliable and reproducible. After transection, there was a mean increase in latency 1 and decreases in latency 2, integrated average area, muscle action potential duration, amplitude, and conduction velocity for all 3 groups. When the groups were compared after transection, the anti-BDNF group showed a significant decrease in conduction velocity and muscle action potential duration (Kruskal-Wallis P = .01 and P = .008, respectively) compared with the other groups. There were no statistically significant differences in latencies, amplitude, or area among the groups. Conclusions: We have established an electrophysiologic model for objective assessment of facial nerve function in the rat. Future studies should combine functional electrophysiologic assessment and histologic examination to provide a more robust model for studying the effects of neurotrophic factors on facial nerve reinnervation and synkinesis.