Changes in neurotrophic factors of adult rat laryngeal muscles during nerve regeneration

- Neurotrophic factors (NTF) expressed in laryngeal muscles following nerve injury.
- NGF, BDNF, and Netrin-1 showed differences among abductor and adductor muscles.
- Whereas, NT-3, NT-4, and TLR-4 did not show difference in expression.
- The emergence of NTF expression timing will promote selective motor reinnervation.

Injury to the recurrent laryngeal nerve (RLN) leads to the loss of ipsilateral laryngeal fold movement, with dysphonia, and occasionally dysphagia. Functional movement of the vocal folds is never restored due to misrouting of regenerating axons to agonist and antagonist laryngeal muscles. Changes of neurotrophic factor expression within denervated muscles occur after nerve injury and may influence nerve regeneration, axon guidance and muscle reinnervation. This study investigates the expression of certain neurotrophic factors in the laryngeal muscles during the course of axonal regeneration using RT-PCR. The timing of neurotrophic factor expression was correlated to the reinnervation of the laryngeal muscles by motor axons. Nerve Growth Factor (NGF), Brain-Derived Neurotrophic Factor (BDNF) and Netrin-1 (NTN-1) increased their expression levels in laryngeal muscles after nerve section and during regeneration of RLN. The upregulation of trophic factors returned to control levels following regeneration of RLN. The expression levels of the neurotrophic factors were correlated with the innervation of regenerating axons into the denervated muscles. The results suggest that certain neurotrophic factor expression is strongly correlated to the reinnervation pattern of the regenerating RLN. These factors may be involved in guidance and neuromuscular junction formation during nerve regeneration. In the future, their manipulation may enhance the selective reinnervation of the larynx.