Evaluation of distal facial nerve branches contribution to facial nerve paralysis in rodents

Introduction/Aims: Facial nerve paralysis is a complex and devastating condition. Translational research of facial paralysis recovery remains largely limited to animal studies, for which there are many potential models employed. When studying facial nerve regeneration in rodents, it is important to understand the converging contributions of the motor supply into the whisker pad. A consensus surgical approach and animal model has yet to be defined. Of particular interest for movement of the nose and whiskers are the buccal and marginal mandibular nerves. This study aims to evaluate how these distal nerve branches contribute to facial nerve paralysis and identify key morphological changes at the neuromuscular junctions (NMJs) in the whisker pad of rodents. Methods: Adult rats underwent isolated transection of the buccal branch of the facial nerve, both the buccal and marginal mandibular branches of the facial nerve, or control sham surgery. Results: Histological, electrophysiological, and behavior assessments confirmed that the transection of the buccal branch alone did not cease whisker movement in rats, but when combined with a transection of the marginal mandibular branch, it resulted in full paralysis of the whisker and nose movement. Discussion: These results are indicative of the distinct roles of these nerves branches in facial paralysis repair following a transection injury. Further, our results suggest additional targets for facial nerve repair treatments.