Effects of unilateral nasal obstruction on the characteristics of jaw-closing muscles in growing rats

Abstract

Mouth breathing caused by nasal obstruction (owing to abnormal pressure of masticatory muscles) affects craniofacial growth and development. The influence of unilateral nasal obstruction on jaw-closing muscles was investigated in rats to reveal one of the etiologic mechanisms. Forty 8-day-old male Wistar rats were used in this study. Experimental rats were subjected to left-sided nasal obstruction by burning the external nostril tissue at the age of 8 days. Pulse oxygen saturation was recorded each week. Morphologic changes were evaluated by staining with hematoxylin and eosin (to assess the cross-sectional area) and by adenosine triphosphatase activity staining (to assess the myosin heavy chain isoform composition). Immunohistochemical and reverse transcription quantitative real-time polymerase chain reaction analyses of tumor necrosis factor-α and glucose transporter 4 were carried out at 5 and 9 weeks of age. The cross-sectional area of the jaw-closing muscles was lower in the experimental group at 9 weeks of age. The percentage of myosin heavy chain-2a in masseter muscles was increased in the experimental group compared with the control group. An increase in the tumor necrosis factor-α messenger RNA and protein levels and a decrease in the glucose transporter 4 messenger RNA and protein levels at 5 and 9 weeks of age in the jaw-closing muscles in the experimental group were noted. Unilateral nasal obstruction could affect the morphology and contractile characteristics of jaw-closing muscles during growth in rats.