Non-recovery animal model of severe facial paralysis induced by freezing the facial canal.

Objective: Some cases of peripheral facial paralysis are resistant to treatment, thus, a non-recovery model of facial paralysis is needed to develop new treatment strategies for this condition. The purpose of the current study was to develop an animal model of which facial palsy was severe and prolonged.

Methods: Ten 8-week-old female Hartley guinea pigs weighing between 400 and 500 g were used for the animal model. The vertical segment of the facial canal was accessed via the otic bulla, without removing the bony wall of the facial canal. The canal was then frozen for 5 s using freeze spray. Facial movements, electroneurography (ENoG), histology, and changes in temperature were evaluated.

Results: All animals exhibited complete facial paralysis immediately after the procedure and recovered gradually, however, not all of them had recovered completely 15 weeks after freezing. The ENoG values one week after freezing for all animals (10/10) were 0%. Histological examination one week after freezing revealed that most of the vertically placed myelinated nerve fibers which had been frozen were remarkably affected and denatured. The number of vertically placed myelinated nerve fibers increased 15 weeks after freezing, but the nerve fibers were smaller than normal nerve fibers and were distorted in shape.

Conclusion: Complete facial paralysis was induced in Hartley guinea pigs by freezing the facial canal. The behavioral, ENoG, and histopathological data suggest that the facial paralysis was severe and prolonged. This model may assist in developing novel treatment for severe facial palsy and facilitate basic research on facial nerve regeneration.