Effects of long-term denervation on the rat thyroarytenoid muscle

To determine the effects of long-term denervation on the rat thyroarytenoid (TA) muscle and neuromuscular junctions.

A quantitative histologic assessment of the TA muscle after long-term denervation.

Thirty Wistar rats were euthanized 10, 18, 26, 42, and 58 weeks after left recurrent laryngeal nerve resection. The areas of the entire muscle and individual muscle fibers were evaluated using hematoxylin-eosin staining, and neuromuscular junctions were detected by immunohistochemistry. Changes after denervation were evaluated by comparing the treated (T) and untreated (U) sides (T/U ratio). The ratio of the number of nerve terminals (NTs) to that of acetylcholine receptors (AChRs) (NT/AChR ratio) was also assessed.

The average T/U ratio for the entire muscle area of the denervation groups ranged between 61.1% and 72.5% and did not differ significantly. Similarly, the T/U ratios for the individual muscle fiber area ranged between 45.0% and 51.9%, and the differences were not significant. The T/U ratio of AChRs at 58 weeks (35.3 +/- 20.2%) was significantly lower than that at 10 weeks (76.3 +/- 9.0%; P < .01). The NT/AChR ratios ranged between 30.3% and 35.6% and did not differ significantly among the denervation groups.

The entire TA muscle area, individual muscle fiber area, and NT/AChR ratio did not decrease with long-term denervation. Thus, the TA muscle may retain an ability to receive regenerating nerve axons. However, the ability of the TA muscle to receive nerve axons may deteriorate after an excessively long denervation period because the T/U ratio of AChRs decreased with long-term denervation.