Abstract
After denervation of the recurrent laryngeal nerve (RLN), the innervated laryngeal muscles are atrophied. We have reported that functional electrical stimulation (FES) delivered to the thyroarytenoid (TA) muscle prevents muscle atrophy after denervation. The reason why FES prevents atrophy of the muscle is not yet clear.
In this study, we tried investigating a hypothesis that the superior laryngeal nerve (SLN) might have a role in preventing muscle atrophy by FES. We used 23 adult rats in this study. Resections of the left SLN with the left RLN, or bilateral SLNs with the left RLN were performed. A pair of thin wire stimulation electrodes (50 u m) was placed in the left TA muscle. The animals were divided into two groups : a stimulated group and a non-stimulated group. In the stimulated group, FES, with 2 mA rectangular pulses of 0.2 ms duration at 2 Hz lasting for 1 hour, was delivered to the TA muscle once every 2 days. After the stimulation periods of 2 or 4 weeks, frontal sections of the larynx 8 pm in thickness were prepared. The differences in the area of the TA muscle, the area of the TA muscle fiber and the density of the TA muscle fiber were compared between the denervated (left) side and the non-denervated (right) side.
Atrophy of the TA muscle was observed in spite of the ipsilateral and/or bilateral denervation of the SLN. The effect of FES to prevent muscle atrophy was also observed regardless of SLN resection. The results obtained from this study suggested that the information to the central nervous system through the SLN was not indispensable for preventing muscle atrophy after denervation of RLN.
