Neurotrophin expression and laryngeal muscle pathophysiology in response to recurrent laryngeal nerve-crush injury

Laryngeal palsy often results from recurrent laryngeal or vagal nerve injury during oncologic surgery of the head and neck. The aim of this study was to describe the characters of spontaneous reinnervation in rats following recurrent laryngeal nerve (RLN) crush injury. Twenty-five male Sprague-Dawley rats each were subjected to a 5-mmlong crush injury to the right recurrent laryngeal nerve. Vocalization, vocal fold movements, histological factors (e.g., axonal diameters, axon numbers), and immunostaining measures of neurotrophin activity were recorded at different time points (i.e., 3 weeks, 6 weeks, 10 weeks, and 16 weeks) following injury. Results showed that vocalization and vocal fold movement were restored at week 16. The expression of brain-derived neurotrophic factor (BDNF) and glial-cell-line-derived neurotrophic factor (GDNF) was different in thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles. The number of axons returned to baseline at week 16, whereas axon diameter was not statistically significantly different between the injured and control axons at week 10. During regeneration of RLN, differences in the expression of neurotrophic factors may lead to the preferential reinnervation of TA. The study shows that application of neurotrophic factors could help restore recurrent laryngeal nerve function.