Despite favorable clinical results, histological and physiological mechanisms remain unknown. First, an end‐to‐side neurorrhaphy is performed between the affected facial nerve trunk and hypoglossal nerve for continuously delivering stimuli to the mimetic muscles for preventing the atrophy of mimetic muscles. The “babysitter” procedure is a reconstruction technique for facial nerve complete paralysis and uses the movement source from the healthy facial nerve with a cross‐nerve graft. This method is expected to be very useful in future studies of facial nerve regeneration for long nerve defects in sheep.

We have established a percutaneous measurement method for CMAP of the buccal branch of the facial nerve in sheep. Mean values for electrophysiological parameters were amplitude 4.7 ± 0.7 mV, duration 2.1 ± 0.6 ms, and latency 3.6 ± 0.4 ms. Percutaneous CMAP measurements of the nasolabial levator muscle could be obtained in all animals by placing stimulating electrodes 1 cm apart on the line coinciding with the course of the buccal branch of the facial nerve revealed by the preceding anatomical exploration. Under general anesthesia, an anatomical exploration was performed to identify the course of the buccal branch of the facial nerve and its innervating muscles on one side, followed by the application of surface stimulating electrodes to the contralateral side of the face along the course of the buccal branch of the facial nerve to obtain CMAP measurements of the nasolabial levator muscle. Six 3-year-old castrated male Corriedale sheep were used in this study. In this study, we developed a percutaneous measurement method for the evoked compound muscle action potential (CMAP) of the facial nerve in sheep. Large-animal models such as sheep for facial nerve regeneration research have not yet been established because of the lack of methods for assessing the electrophysiological function of regenerated nerves. However, the above rat models of facial nerve defect allowed for experimental nerve transplantation into defects of up to only about 7 mm in length due to the small size of the animals, and were too small to reproduce facial nerve regeneration surgery in human patients in clinical practice. We then developed a method to measure compound muscle action potential (CMAP) in these rat models of facial nerve regeneration, for which no electrophysiological evaluation method for regenerated facial nerves had been established. Toward establishing new surgical treatments for facial nerve palsy, we have developed various experimental systems for facial nerve regeneration using rat models of facial nerve defects, including facial nerve regeneration in rats using a novel nerve conduit made of polylactic acid nonwoven fabric, facial nerve regeneration in rats using a basic fibroblast growth factor drug delivery system, facial nerve regeneration using dedifferentiated fat cells, facial nerve regeneration using adipose-derived stem cells (ADSCs) that were induced in vitro to differentiate into Schwann cell lineages, facial nerve reconstruction in rats using an artificial nerve conduit containing dental pulp cells extracted from incisor teeth, and facial nerve regeneration using an artificial nerve conduit made of a silicone tube containing a non-cultured stromal vascular fraction as the source of ADSCs.

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