Browsing by Subject "Masseter muscle"

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    Expression of myostatin in early postnatal mouse masseter and rectus femoris muscles
    (Universidad de Murcia. Departamento de Biología Celular e Histología, 2015) Takada, Hiroshi; Miwa, Yoko; Sato, Iwao
    Aims: Myostatin (Mstn) is a member of the transforming growth factor-β (TGF-β) family that inhibits muscle differentiation. In this study, we aimed to identify the relationships between Mstn, thyroid hormone receptor alpha (TRα), and myosin heavy chain (MyHC) isoform expression during early postnatal development. Methods: We investigated the expression of Mstn, TRα, and MyHCs (embryonic, slow, IIa, IIb, and IIx) using quantitative real-time RT-PCR and ELISA (Mstn) in postnatal mouse muscles between day 0 and day 10. We also examined the correlations between Mstn, TR and MyHCs during the early development of mouse masseter muscle (MM) and rectus femoris muscle (RFM). Results: Distinct Mstn mRNA expression patterns were observed in the two muscles despite nearly non-significant changes in the Mstn protein abundance in MM. The expression pattern of the TRα mRNA in the MM differed from that observed in the RFM. The expression of MyHC IIa, IIb and IIx mRNAs increased in the MM and decreased in the RFM from day 0 to day 10, whereas embryonic fiber MyHC mRNA expression was similar in both muscle types. Principal component analysis showed the existence of a correlation between: (1) TRα and MyHC, (2) Mstn and MyHC, and (3) TRα and Mstn in MM. The correlations were different in RFM and MM. Cluster analyses identified the distinct clusters: cluster 1, days 0-4 for the MM and day 0 for the RFM;cluster 2, day 6 for the MM and day 2 for the RFM; and cluster 3, days 8-10 for the MM and days 4-10 for the RFM. Conclusions: These data suggest that TRα influences MyHC expression in both muscle types. In addition, Mstn has a limited effect in the MM related to the expression of individual MyHCs, as opposed to its role in the RFM, at early postnatal developmental stages. TRα could be involved in regulating both the temporal expression of MyHCs and Mstn at the early postnatal stages in the MM and RFM.
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    Ultrastructural abnormalities of muscle spindles in the rat masseter muscle with malocclusion-induced damage
    (Murcia : F. Hernández, 2002) Bani, D.; Bergamini, M.
    Human temporomandibular disorders due to disturbed occlusal mechanics are characterized by sensory, motor and autonomic symptoms, possibly 1 related to muscle overwork and fatigue. Our previous study in rats with experimentally-induced malocclusion due to unilateral molar cusp amputation showed that the ipsilateral masseter muscles undergo morphological and biochemical changes consistent with muscle hypercontraction and ischemia. In the present study, the masseter muscle spindles of the same malocclusionbearing rats were examined by electron microscopy. Sham-operated rats were used as controls. In the treated rats, clear-cut alterations of the muscle spindles were observed 26 days after surgery, when the extrafusal muscle showed the more severe damage. The fusal alterations affected predominantly capsular cells, intrafusal muscle fibers and sensory nerve endings. These results suggest that in the malocclusion-bearing t rats, an abnormal reflex regulation of the motor activity of the masticatory muscles may take place. They also allow us to hypothesize that muscle spindle alterations might be involved in the pathogenesis of human temporomandibular disorders.