Abstract
Using 38 guinea pigs with unpaired arytenoid muscle (AR), the innervation pattern of the AR was studied viewed from reinnervation process following unilateral (left) recurrent laryngeal nerve (RLN) transection. Light and electron microscopic observation, glycogen depletion experiment, and histochemical study using the adenosine triphosphatase (ATPase) stain were carried out.
Seven days after transection, both myelinated and unmyelinated fibers were noted in the intramuscular nerve funiculus. Thus, the anastomosis of the arytenoid branches between both RLNs was found in the belly of AR. Three types of the neuromuscular junctions (NMJs) were observed; normal, degenerated, and regenerated NMJs. Five weeks after transection, however, neither degeneration nor regeneration of the NMJ were seen.
Until three weeks after transection, half of the AR fibers were stained with PAS staining following electrical stimulation of the contra lateral (right) RLN. Five weeks after transection, all the AR fibers were unstained. Therefore, all the AR fibers were considered to have been reinnervated by the contra lateral RLN.
ATP stain of the AR showed that type 2 fibers were predominant regardless of the period following unilateral denervation.
The present study indicates that transection of the unilateral RLN facilitates collateral sprouting from the contra lateral RLN, and that these collateral sprouting reinnervated the denervated muscle fibers before degeneration occurs. Therefore the AR, as a whole, receives a specific motor innervation from the bilateral RLNs, although each muscle fiber is innervated by the unilateral RLN.
