title: Heterogeneity of fiber characteristics in the rat masseter and digastric muscles.
abstract: The functional requirements in muscle use are related to the fiber type composition of the muscles and the cross-sectional area of the individual fibers. We investigated the heterogeneity in the fiber type composition and fiber cross-sectional area in two muscles with an opposing function, namely the digastric and masseter muscles (n = 5 for each muscle) of adult male rats, by means of immunohistochemical staining according to their myosin heavy chain (MyHC) content. The digastric and masseter muscles were taken from Wistar strain male rats 10 weeks old. In the masseter six predefined sample locations were examined; in the digastric four. Most regions showed dominant proportions of type IIA and IIX fibers. However, both muscles also revealed a regional heterogeneity in their fiber type distribution. In the digastric, type I fibers were detected only at the central and deep areas of the anterior and posterior belly, respectively. Meanwhile, the peripheral area of the anterior belly contained a higher proportion of type IIB fibers. In the masseter, the type I fibers were absent. In the superficial masseter the distribution of IIA and IIB fibers was significantly different between the superior and inferior regions. In the deep masseter, regional differences were observed among all four examined areas, of which the posterolateral region contained the highest proportion of type IIB fibers. The cross-sectional areas of type IIB fibers were always the largest, followed by the type IIX and IIA fibers. Only a few differences in cross-sectional area of corresponding fiber types were detected between the various sites. In conclusion, the masseter and digastric muscles showed an obvious heterogeneity of fiber type composition and fiber cross-sectional area. Their heterogeneity reflects the complex role of the both muscles during function. This detailed description of the fiber type composition can serve as a reference for future studies examining the muscular adaptations after the onset of various diseases in the masticatory system.
authors: Department of Orthodontics and Craniofacial Developmental Biology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan. george-s1479@hiroshima-u.ac.jp
authors: R
authors: R
authors: Sano
authors: E
authors: E
authors: Tanaka
authors: J A M
authors: JA
authors: Korfage
authors: G E J
authors: GE
authors: Langenbach
authors: Nobuhiko
authors: N
authors: Kawai
authors: T M G J
authors: TM
authors: van Eijden
authors: K
authors: K
authors: Tanne
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000032:analysis; D007150:Immunohistochemistry; D008297:Male; D008406:Masseter Muscle / Q000166:cytology* / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000166:cytology*; D018995:Myosin Heavy Chains / Q000032:analysis; D009334:Neck Muscles / Q000166:cytology* / Q000502:physiology; D020033:Protein Isoforms / Q000032:analysis; D051381:Rats
chemical_list: D015415:Biomarkers; D020033:Protein Isoforms; D018995:Myosin Heavy Chains
references: J Physiol. 1996 Sep 1;495 ( Pt 2):573-86
references: 8887767
references: J Anat. 2001 Mar;198(Pt 3):283-94
references: 11322721
references: J Oral Maxillofac Surg. 1990 Oct;48(10):1063-7
references: 1698954
references: J Anat. 2006 Jun;208(6):743-51
references: 16761975
references: Rev Physiol Biochem Pharmacol. 1992;120:115-202
references: 1519018
references: J Dent Res. 2005 Sep;84(9):784-93
references: 16109985
references: Histochem J. 1991 Apr;23(4):160-70
references: 1836206
references: Int Rev Cytol. 1997;170:143-223
references: 9002237
references: Eur J Oral Sci. 2007 Feb;115(1):15-20
references: 17305712
references: J Appl Physiol (1985). 1996 May;80(5):1503-12
references: 8727533
references: J Anat. 1990 Feb;168:31-47
references: 2139021
references: J Muscle Res Cell Motil. 1995 Feb;16(1):21-34
references: 7751402
references: Exp Brain Res. 1997 Jun;115(2):325-32
references: 9224860
references: J Physiol. 1983 May;338:37-49
references: 6875963
references: Arch Neurol. 1970 Oct;23(4):369-79
references: 4248905
references: J Physiol. 1993 Dec;472:595-614
references: 8145163
references: J Neurophysiol. 1995 Feb;73(2):538-49
references: 7539059
references: Can J Appl Physiol. 2002 Aug;27(4):423-48
references: 12442355
references: Muscle Nerve. 2000 Jul;23(7):1095-104
references: 10883005
references: Science. 1978 Apr 21;200(4339):314-7
references: 635587
references: Sports Med. 2004;34(12):809-24
references: 15462613
references: J Physiol. 1996 May 1;492 ( Pt 3):659-67
references: 8734979
references: Neurosci Lett. 1982 Aug 31;31(3):247-52
references: 6752764
references: J Appl Physiol (1985). 1996 Nov;81(5):2004-12
references: 8941522
references: Physiol Rev. 1996 Apr;76(2):371-423
references: 8618961
references: J Physiol Sci. 2006 Jun;56(3):205-9
references: 16839454
references: Eur J Neurosci. 2005 Dec;22(11):2783-91
references: 16324112
references: J Musculoskelet Neuronal Interact. 2003 Dec;3(4):391-4; discussion 406-7
references: 15758330
references: J Appl Physiol (1985). 2001 Jan;90(1):345-57
references: 11133928
references: J Histochem Cytochem. 1984 Jun;32(6):655-60
references: 6202737
references: J Dent Res. 2005 Sep;84(9):774-83
references: 16109984