A new model for facial nerve research: The novel transgenic Thy1-GFP rat

Objective: To introduce a Thy1-GFP transgenic rat model, whose axons constitutively express green fluorescent protein (GFP), in order to study facial nerve regeneration. Facial nerve injury can cause devastating physical and social sequelae. The functional recovery of the facial nerve can result in synkinesis and permanent axonal misrouting. Facial nerve research has been hindered by the lack of available animal models and reliable outcome measures. Methods: Transgenic Thy1-GFP rats underwent a proximal facial nerve crush injury and were imaged at 0, 1, 2, 4, and 8 weeks after injury. Nerve regeneration was assessed via confocal imaging and fluorescence microscopy. Results: Uninjured animals reliably demonstrated facial nerve fluorescence and had predictable anatomical landmarks. Fluorescence microscopy demonstrated the loss and reappearance of fluorescence with regeneration of axons following injury. This was confirmed with the visualization of denervation and reinnervation of zygomaticus muscle motor end plates using confocal microscopy. Conclusions: The Thy1-GFP rat is a novel transgenic tool that enables direct visualization of facial nerve regeneration after injury. The utility of this model extends to a variety of clinical facial nerve injury paradigms.