Developmental changes in histochemical properties of intrinsic laryngeal muscles in rats.
OBJECTIVE
Using neonatal rats, the developmental changes in muscle fiber type of the intrinsic laryngeal muscles were analyzed. The potential influence of two factors were also studied, that were predicted would influence developmental changes in muscle fiber type, denervation and hypothyroidism.


METHODS
Using the histochemical technique of myosin ATPase staining, postnatal changes in the ratio of muscle fiber types of each intrinsic laryngeal muscle were determined. In addition, to clarify factors influencing the development of the intrinsic laryngeal muscles, the same technique was employed to study recurrent laryngeal nerve-denervated rats and rats with experimentally-induced hypothyroidism.


RESULTS
In normal pups, type 2C fibers had almost disappeared by postnatal day (PND) 14. In denervated pups, differentiation to type 1 and 2A muscle fibers was not observed. In contrast, differentiation to type 2B muscle fibers was impaired in the hypothyroid pups.


CONCLUSIONS
The differentiation of intrinsic laryngeal muscles occur earlier than that of hindlimb muscles. Each intrinsic laryngeal muscle exhibits a particular pattern of developmental changes in normal pups. The developmental changes in the intrinsic laryngeal muscles are affected by recurrent laryngeal nerve innervation and thyroid hormonal control. The findings suggest that both recurrent laryngeal nerve innervation and thyroid hormone play important roles in the differentiation of the intrinsic laryngeal muscles.
Hangai
K
K
Department of Otolaryngology, Asahikawa Medical School, Japan.
Kobayashi
Y
Y
Nonaka
S
S
D000818:Animals; D001284:Atrophy / Q000473:pathology; D003714:Denervation; D007037:Hypothyroidism / Q000175:diagnosis / Q000201:enzymology; D007821:Laryngeal Muscles / Q000201:enzymology / Q000294:innervation / Q000473:pathology*; D007830:Larynx / Q000473:pathology; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000473:pathology; D009218:Myosins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley / Q000254:growth & development; D012009:Recurrent Laryngeal Nerve / Q000201:enzymology / Q000473:pathology / Q000601:surgery
D009218:Myosins