Effects of denervation on neuromuscular junctions in the thyroarytenoid muscle.

OBJECTIVES/HYPOTHESIS: To evaluate the effects of denervation on muscle fibers and neuromuscular junctions (NMJ) of the rat thyroarytenoid (TA) muscle with a histochemical method to monitor the status of degenerative NMJ.

STUDY

DESIGN

Quantitative assessment to monitor the status of degenerative muscle fibers and NMJ in the TA muscle.

METHODS

Wistar rats were killed at 6, 12, 18, and 24 hours and at 2, 4, and 10 weeks after left recurrent laryngeal nerve (RLN) transection. Hematoxylin-eosin stain was used to evaluate the atrophic changes of the TA muscle. The pre- and postsynaptic structures of the NMJ were detected histochemically. These changes were evaluated by comparing the results between the treated (T) and untreated (U) sides (T/U ratio) in the same section.

RESULTS

The atrophic changes in the TA muscle progressed gradually, and at 10 weeks, the T/U ratios of the entire muscle area and of the muscle fiber size decreased to 53.2 +/- 10.7% and 55.5 +/- 6.8%, respectively (P < .01). The number of nerve terminals decreased significantly at 18 hours (P < .01), and they disappeared completely by 24 hours. In contrast, at 10 weeks, 70.5 +/- 12.4% (P < .01) of acetylcholine receptors (AchRs) were preserved.

CONCLUSIONS

In the rat TA muscle, denervation influences the presynaptic nerve terminals more than the postsynaptic AchRs and the muscle fibers. The results could be a basis for understanding the mechanism of laryngeal denervation and reinnervation processes in animal models.