The Relationship between Functional Recovery and Reorganization of Nucleus Ambiguus Following Laryngeal Reinnervation in Rats

Chung, Sung Min; Hong, Hyun Jeong; Yoon, Sun Ok; Shin, Hye Jung; Park, Su Kyoung; Shin, You Ree; Kim, Jin Kyung

Abstract

BACKGROUND AND OBJECTIVES: Ideally, treatment for vocal cord paralysis should restore normal physiologic and dynamic movement of the vocal fold. Recently, numerous studies of laryngeal reinnervation have been designed to restore function of the paralyzed larynx. None of these approaches have been consistently successful, probably due to synkinesis and an inadequate number of regenerated axons. In previous study, we confirmed the efficacy of PEMS on the early functional recovery in rats with surgically transected and reanastomosed recurrent laryngeal nerve. In this study, the relationship between functional recovery and reorganization of nucleus ambiguus following laryngeal reinnervation in rats was evaluated by retrograde double tracing technique and electron microscope. MATERIALS AND METHOD: Transections and primary anastomosis were done on left recurrent laryngeal nerves of 86 healthy male Sprague-Dawley rats. Rats were then randomly assigned to 2 groups (the group A: stimulation with PEMS, the group B: non-stimulation with PEMS). Functionally recovered status was confirmed with laryngo-videostroboscopy and laryngeal EMG. And then, functional reorganization of laryngeal motoneuron in the nucleus ambiguus (NA) was evaluated using retrograde double tracing techniques. Morphological changes of the degeneration and regeneration processes following injury was observed by electron microscopy.
RESULTS
20 rats (63%) in group A and 5 rats (17%) in the group B showed recovery of vocal fold motion. The functional reorganization of laryngeal motor neurons in the NA was observed in the rats with functional recovery (n=8), but not in the rats without functional recovery (n=8). In the electron microscopic finding, the nerve fibers of functional recovered rats were relatively well regenerated. But the configuration of the nerve fibers of non-functionally recovered rats was markedly irregular and the total axon population was smaller than that of the recovered rats, except for some cases.
CONCLUSION
This study shows that failure of functional recovery of vocal fold movement following laryngeal reinnervation is probably due to not only the misdirected reinnervation, but also the incomplete axonal regeneration.