Reinnervation of the Arytenoid Muscle after Unilateral Denervation

Abstract

Dual motor innervation by the bilateral recurrent laryngeal nerves (RLNs) has been described in the human arytenoid muscle (AR). It has been thought that AR has single motor innervation at the level of muscle fibers. Following unilateral denervation, however, AR presents no morphological evidences of denervation including muscular degeneration and atrophy. The purpose of this study was to investigate the reason why unilateral denervation did not cause evidences of denervation in AR.
The location of the neuromuscular junctions (NMJ) in AR of guinea pigs was determined with the use of acetylcholine esterase stain by Karnovsky. Guinea pigs have unpaired type of AR, like human beings do. In guinea pigs NMJs of AR were located near the midline. Following unilateral denervation, both NMJ and terminal axons were investigated by means of silver-cholinesterase immunocytochemistry stain by Pestronk. The investigation was conducted three days and five weeks after section of a unilateral vagus nerve. The distal cut end of the nerve was placed far away from the proximal end. Three days after denervation, approximately one half of the NMJs had no terminal axon. Five weeks following denervation approximately 80 percent of NMJs had a terminal axon. The terminal axons for the denervated NMJs should have come from sprouting of the contralateral recurrent laryngeal nerve.