Impact of buccal and marginal mandibular branch transection on neuromuscular junction integrity in a rodent model of facial nerve paralysis.

Abstract

BACKGROUND: Facial nerve paralysis is a complex and devastating condition, with translational research primarily relying on animal models. Models include injuries to the main trunk or distal branches of the facial nerve, such as the buccal and marginal mandibular branches. While recovery is well described following main trunk injury, this study investigates the impact of distal branch injuries on facial nerve recovery and neuromuscular junction (NMJ) innervation. NEW METHOD: Adult rats underwent transection of the buccal branch (BB) or of the buccal and marginal mandibular branches (BB+MM) of the facial nerve and were compared to sham controls. Facial palsy scores, compound muscle action potentials (CMAP), and NMJ innervation were quantified to assess chronic paralysis. RESULTS: BB transection alone did not result in prolonged facial palsy, as facial palsy scores and CMAPs remained comparable to sham conditions. However, BB+MM transection reduced NMJ innervation by 50 % and induced whisker and nose paralysis. Pre- and post-synaptic morphology metrics were significantly reduced in the BB+MM group, whereas the BB group NMJs resembled the morphology to the NMJs in the sham group. COMPARISON WITH EXISTING METHODS: These results expand existing studies by providing quantitative insights into NMJ innervation and demonstrating the complete loss of nasal mobility following the combined distal branch injury model. CONCLUSIONS: These results provide further model characterization of distal facial nerve branches contribution to NMJ integrity and nasal mobility. This model will serve as a testbed for future biomaterials in facial nerve injury, incorporating comprehensive characterization techniques to assess repair and function.