Plastic Surgery Research Council
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Presenter: Maria C Alvarez Veronesi, MC
Co-Authors: Placheta E; Lafontaine CA; Liu E; Wood MD; Gordon T; Frey M; Borschel GH
University of Toronto

Background: Cross-face nerve grafts are used in cases of unilateral facial paralysis for direct innervation of paralyzed facial muscles or to power muscle transplants. Regeneration of facial nerve axons through the grafts takes several months and cross-face nerve grafts often support insufficient axon regeneration. We hypothesize that the loss of the pro-regenerative state within long grafts results in incomplete regeneration. We propose that donor axons from sensory nerves can maintain the growth-permissive state within the grafts and, in turn, increase axon regeneration.

Methods: In a rat model, the common peroneal nerve was used as a cross-face nerve graft (30mm). It was coapted end-to-end from the right buccal branch of the facial nerve (donor branch) to the buccal and mandibular branches of the left facial nerve (recipient side). In a second group, both occipital nerves were coapted end-to-side to the cross-face nerve graft through epineurial windows. In transgenic Thy1-GFP rats, whose axons express the fluorescent marker GFP, axon regeneration was imaged in-vivo at 4, 8, 12, and 16 weeks postoperatively. Regenerating axons were retrogradely labeled distal to the cross-face nerve graft after 16 weeks and nerve samples were collected for histomorphometry analysis.

Results: In the Thy1-GFP rats, axon regeneration through the grafts was successfully imaged in vivo. After 8 weeks, the regenerating axons reached the recipient facial nerve branches in the protected group, whereas they did not in the unprotected group. Retrograde labeling and histomorphometry analysis revealed that the number of regenerating motoneurons (30424 unprotected; 40227 protected, p=0.0184) and the number of myelinated axons regenerating in the buccal branch after 16 weeks (1655127 unprotected; 2672357.2 protected, p=0.0152) were significantly increased in the group with protection.

Conclusion: Motor axon regeneration through the cross-face nerve grafts was improved by occipital nerve end-to-side protection. The Thy1-GFP rat model was effective for imaging in vivo nerve regeneration through the cross-face nerve grafts.

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