ABSTRACT
The masseter muscle (MM) is a complex tendinous laminar structure during development; however, the stage of the laminar structure formation is unknown. Tenomodulin (TeM) is a useful marker of tendons and has an anti-angiogenic cysteine-rich C-terminal domain. Therefore, we analyzed mRNA of TeM and angiogenesis markers (CD31 and vascular endothelial growth factor (VEGF)) and performed in situ hybridization for the TeM genes in MM from on embryonic day 12.5 (E12.5) to postnatal day 5 (P5). The TeM expression is at first detectable in the middle region of the mesenchymal connective tissue in the MM at E 12.5. The expression domains of the TeM during development typically include the middle region of the MM, particularly surrounding the vascular regions. The level of TeM mRNA in the MM increased from E12.5 to E17.5 and decreased after birth. In contrast, the levels of CD31 and VEGF mRNAs were almost constant from E12.5 to E18.5 and then low from birth onward. Therefore, the development of the laminar tendinous structure in the middle region between superficial and deeper regions of the MM first occurs during the process of tendon formation at embryonic day 12.5. In our study of MM development, the laminar structure regulating TeM also prevents vascular invasion during the formation of compartment of the MM. The tendon may relate to the components of muscle mass of MM.
Subject(s)
Masseter Muscle/embryology , Masseter Muscle/metabolism , Membrane Proteins/metabolism , Platelet Endothelial Cell Adhesion Molecule-1/metabolism , Tendons/embryology , Tendons/metabolism , Vascular Endothelial Growth Factor A/metabolism , Aging/metabolism , Aging/pathology , Animals , Animals, Newborn , Gene Expression Regulation, Developmental/physiology , Mice , Mice, Inbred C57BL , Neovascularization, Physiologic/physiology , Tissue DistributionABSTRACT
UNLABELLED: We examined the effect of a standardized painful stimulus on the surface EMG-activity of the human jaw-closing muscles at rest and during two levels of jaw opening. Sixteen healthy women participated in two experimental sessions. In randomized order, hypertonic saline (HS: 5.8%) was infused into the left masseter muscle on one occasion, and isotonic saline (IS: 0.9%) on the other. The subjects scored the pain intensity continuously on a 0-10 visual analogue scale (VAS). The subjects were asked to hold the jaw in three different positions (rest, half-maximal, and maximal opening). Before, during, and after infusion, the EMG-activity was recorded from the masseter and temporalis muscles with the jaw in each of the three positions. HS induced significantly higher pain-levels than IS (mean VAS: HS: 5.2+/-1.3, IS: 0.7+/-0.2, P<0.05). At rest, the EMG-activity in most of the jaw muscles increased significantly during both infusions (P<0.05). At half-maximal opening, the EMG-activity in the infused muscle increased significantly with both HS and IS (P<0.05). At maximal opening, the EMG-activity during infusion of HS decreased significantly in the right masseter and temporalis (P<0.05). There was no significant difference in the position of the jaw at rest during infusions. However, the vertical opening distance was significantly decreased during infusion of HS at half-maximal and maximal opening (P<0.05). CONCLUSIONS: It is concluded that experimental pain affects EMG-activity differentially in jaw-closing muscles in different opening positions of the jaw.
