Synapse formation by autonomic nerves in the previously denervated neuromuscular junctions of the feline intrinsic laryngeal muscles

Abstract

Nerve terminals of unknown origin at the previously denervated neuromuscular junctions (NMJ) of the feline intrinsic laryngeal muscles were investigated. Until 3 weeks after the transection of the recurrent laryngeal nerve (RLN), no axons were observed in the Büngner's bands and the NMJ, accompanied by a marked decrease of autonomic nerves around the blood vessels. At 5–6 weeks nerve varicosities labeled by 5-hydroxydopamine (5-OHDA) were observed in the Büngner's bands together with an increase of autonomic nerves around the blood vessels. At 9–30 weeks (8 cases) nerve terminals were found at the NMJ in all cases. Even if the ipsilateral vagosympathetic trunk was transected at 17 weeks, nerve terminals were found at all the NMJ 3 weeks after this treatment, indicating that nerve terminals were not from the original RLN. These nerve terminals were considered to be autonomic because nerve terminals labeled by 5-OHDA were observed. Furthermore, in the case of the removal of the superior cervical ganglion (SCG) and the nodose ganglion at 21 weeks, though nerve varicosities were found in the Büngner's bands, nerve terminals were not found 9 days after this treatment, suggesting that the ipsilateral SCG possibly played an important role. In electromyographic findings fibrillation-like activities were recognized in 8/11 cases after 5 weeks. The relationship of this phenomenon to fibrillation and muscle atrophy was discussed.