Related Experiment Videos
Developmental changes in histochemical properties of intrinsic laryngeal muscles in rats
K Hangai1, Y Kobayashi, S Nonaka
1Department of Otolaryngology, Asahikawa Medical School, Japan.
Insights
Neonatal rat laryngeal muscle development shows early fiber type differentiation. Recurrent laryngeal nerve denervation and hypothyroidism significantly disrupt this process, highlighting their crucial roles.
Area of Science:
- Developmental biology
- Muscle physiology
- Neuroscience
Background:
- The intrinsic laryngeal muscles are crucial for vocalization and airway protection.
- Understanding their developmental trajectory is essential for diagnosing and treating related disorders.
- Factors influencing muscle development, such as innervation and hormonal status, are key areas of investigation.
Purpose of the Study:
- To analyze developmental changes in muscle fiber type composition of intrinsic laryngeal muscles in neonatal rats.
- To investigate the impact of recurrent laryngeal nerve denervation on these developmental changes.
- To examine the effects of experimentally induced hypothyroidism on intrinsic laryngeal muscle fiber type differentiation.
Main Methods:
- Histochemical analysis using myosin ATPase staining to determine muscle fiber type ratios.
- Comparative study of normal neonatal rats, recurrent laryngeal nerve-denervated rats, and rats with induced hypothyroidism.
- Assessment of muscle fiber type changes across different postnatal days.
Main Results:
- In normal rats, type 2C muscle fibers largely disappeared by postnatal day 14.
- Denervation prevented the normal differentiation into type 1 and type 2A muscle fibers.
- Hypothyroidism impaired the differentiation into type 2B muscle fibers.
Conclusions:
- Intrinsic laryngeal muscle differentiation occurs earlier than in hindlimb muscles.
- Both recurrent laryngeal nerve innervation and thyroid hormone are critical for the proper differentiation of intrinsic laryngeal muscles.
- These findings underscore the importance of neural and hormonal factors in vocal fold muscle development.
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.
Conclusion:
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.