Inhibition of motor nerve regeneration in a rabbit facial nerve model

Objectives/Hypothesis: We hypothesized that intramuscular injection of vinc ristine into the upper Lip selectively prevents reinnervation of the target muscle (quadratus labii superioris) after facial nerve transection. Study Design: Prospective controlled experiment. Methods: Transection injuries wi th primary neurorrhaphy were performed just proximal to the buccal and zygo matic branches of both facial nerves in 20 rabbits. The left (experimental) quadratus labii superioris muscle was injected with 200 mug vincristine 72 hours after injury; the right (control) side was injected with saline. Fun ctional electrophysiological and histological studies were performed 6 week s after surgery. Results:After 6 weeks, the control side had a mean axon co unt (distal buccal branch) of 1160, conduction velocity of 50.4 mis, reduct ion of compound action potential amplitude of 44%, and functional index of 1.67 units. The experimental side had a mean axon count of 265, conduction velocity of 16.5 mis, reduction of compound action potential amplitude of 8 8%, and a functional index of 0.176 units. All parameters were significantl y reduced by vincristine blockade (P < .05), The zygomatic division (not ex posed to vincristine) displayed a trend toward increased axon counts, but t his was not statistically significant (P = .131), Conclusions: These result s demonstrate that reinnervation of a selected muscle can be prevented by i njection of vincristine, Enhanced reinnervation of adjacent muscle groups m ay also occur. Thus, nerve blockade by vincristine may be useful for the pr evention of synkinesis.