Recurrent laryngeal neuropathy (RLN) is a major cause of poor performance in horses. This disease produces denervation atrophy of the cricoarytenoid dorsalis muscle, which is responsible for maintaining an open airway during exercise. The current treatment relies on the use of a permanent suture, to open the airway and increases the likelihood of complications such as aspiration, coughing, and loss of arytenoid abduction. Together these complications contribute to the moderate post-operative success rate. We propose a regenerative approach to restore normal laryngeal function in horses affected by RLN using an enhanced nerve graft. The approach would avoid interfering with the normal protective mechanisms of the airway and so avoid the complications associated with the current treatment. We hypothesize that manipulation of the microenvironment at the site of nerve anastomosis using nerve growth factor (NGF) will promote Schwann cell migration, axonal regrowth and improve subsequent functional recovery. We will use a novel approach combining lipid microtubules (LMT) with an agarose hydrogel to provide sustained, localized release of nerve growth factor at the site of nerve repair. 

In the first aim, we will verify the optimal in vivo dose of NGF released over five days to promote Schwann cell migration and axon extension. We will use a gap created in the sciatic nerve of rats by the implantation of an inert silicone conduit, filled with the NGF loaded- LMT at three doses which bracket the anticipated optimal dose. A control group consisting of unloaded LMT will also be used. Schwann cell migration and axon extension within the conduit will be assessed using immunohistochemistry. We then test the efficacy of sustained NGF release on nerve regeneration using an experimental paradigm of nerve graft in the rat hind limb. This approach mimics the situation in equine RLN where the distal nerve stump is denervated through axonal loss and demyelination and could be grafted using the second cervical nerve to restore laryngeal function. Common Peroneal (CP) to Tibial (TIB) nerve cross-suture will be performed acutely or two months after TIB nerve transection in rats. In each case, the nerve anastomosis will be supported by surrounding the anastomosis site with NGF-loaded LMT at the optimal dose or unloaded LMT (control).