Improved Functional Recovery After Facial Nerve Reconstruction by Temporary Denervation of the Contralateral Mimic Musculature With Botulinum Toxin in Rats

Abstract

Background. Even optimal nerve reconstruction after facial nerve damage leads to defective reinnervation because of misdirected axonal sprouting and polyinnervation of the end plates of the facial muscles. Objective. The authors studied whether temporary chemical denervation of the contralateral nonlesioned hemiface with botulinum toxin (BTX) would increase regeneration of the lesioned buccal branch of the facial nerve and improve functional recovery of the whisker pad. Methods. The experiments were performed in 65 adult rats distributed in 4 interventions: (1) buccal–buccal nerve anastomosis (BBA), (2) BBA plus ipsilateral injection of BTX into the whisker pad, (3) BBA plus contralateral BTX injection, or (4) BTX injection without any surgery. Sequential preoperative and postoperative retrograde fluorescence tracing at 4 weeks after surgery quantified the accuracy of reinnervation. Functional recovery was measured by biometrical image analysis of whisking behavior at 12 weeks after surgery. Results. After BTX injection without any surgery, muscle paralysis was transient, and the animals restored normal nerve terminals and normal vibrissal function at 8 weeks after treatment. After BBA and ipsilateral or contralateral BTX injection, the degree of correct reinnervation increased significantly to 61% in comparison to 27% after BBA without any other intervention. Enhanced correct reinnervation was accompanied by a significant improvement of whisking after contralateral but not after ipsilateral injection of BTX. Conclusions. These results provide evidence that transient contralateral muscle paralysis helps improve the morphological and functional regeneration after facial nerve repair.