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First published online January 31, 2007
Journal of Experimental Biology 210, 628-641 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02683

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Pushing the limit: masticatory stress and adaptive plasticity in mammalian craniomandibular joints

Matthew J. Ravosa^1,*, Ravinder Kunwar², Stuart R. Stock³ and M. Sharon Stack¹

¹ Department of Pathology and Anatomical Sciences, University of Missouri School of Medicine, M263 Medical Sciences Building, One Hospital Drive DC055.07, Columbia, MO 65212, USA
² Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
³ Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Feinberg School of Medicine, Chicago, IL, USA

View larger version (45K): [in this window] [in a new window]   Fig. 1. MicroCT analysis of symphyseal (A) and TMJ (B) structure in rabbits. (A) Tracing of a coronal section of the middle joint site. In each of five coronal sections, biomineralization levels were evaluated with computer assisted image analysis at five equidistant points along the articular surface (arrows) and four equidistant points along the lateral, superior and inferior cortical bone regions (arrowheads). Symphysis height and width also were quantified (not shown). (B) Tracing of the coronal section of the middle condylar site. In each of three coronal sections, bone-density levels were evaluated with computer-assisted image analysis at five equidistant points along the articular surface (arrowheads), four equidistant subchondral bone locations below the condylar articular cartilage (circles) and three equidistant points along each side of the condylar neck below the articular surface (arrows).

View larger version (96K): [in this window] [in a new window]   Fig. 2. Symphyseal cortical bone thickness. Coronal sections of `middle' joint sites from U-diet (A) and O-diet (B) subadult rabbits obtained via microCT. Comparisons of three size-adjusted measures of internal joint proportions indicate that O-diet rabbits develop significantly thicker cortical bone along the superior, lateral and articular surfaces of the symphysis (red lines with double arrowheads) (see Table 2).

View larger version (138K): [in this window] [in a new window]   Fig. 3. Symphyseal proteoglycan content. Coronal sections (6 µm) of `middle' joint sites from U-diet (A) and O-diet (B) subadults stained with Safranin O to identify GAG content in the FC pad. In the high-power views of the ventral joint with the FC pad, darker staining in A vs B indicates lower proteoglycan content and thus decreased FC pad viscoelasticity in O-diet rabbits. In B note also the corresponding development of bony rugosities (`blue' bone, nearly completely traversing the `red' FC pad).

View larger version (72K): [in this window] [in a new window]   Fig. 4. TMJ proteoglycan content. Coronal sections (6 µm) of middle joint sites from U-diet (A) and O-diet (B) 4-month old subadults were stained with Safranin O to identify GAG content in the articular cartilage. In low-power views of the articular surface and underlying subchondral bone, more intense staining in A vs B indicates lower proteoglycan content and thus diminished articular cartilage viscoelasticity in O-diet rabbits.

View larger version (129K): [in this window] [in a new window]   Fig. 5. Symphyseal type II collagen. Coronal sections (6 µm) of the `middle' joint site in 4-month old U-diet (A) and O-diet (B) subadults stained with a primary antibody directed against type II collagen. In the high-power views of the ventral joint, darker staining in the FC pad of A vs B demonstrates less type II collagen and thus lower viscoelasticity in O-diet rabbits.

View larger version (64K): [in this window] [in a new window]   Fig. 6. TMJ type II collagen. Coronal sections (6 µm) of middle sites in 4-month old U-diet (A) and O-diet (B) subadults were stained with a primary antibody directed against type II collagen. In the low-power views of the articular cartilage and subchondral bone, more intense staining of TMJ articular cartilage in A vs B indicates less type II collagen and thus diminished viscoelasticity in O-diet rabbits.

View larger version (109K): [in this window] [in a new window]   Fig. 7. Symphyseal apoptosis. Coronal sections (6 µm) of `middle' joint sites from U-diet (A) and O-diet (B) subadults tunel stained to identify fragmented DNA of apoptotic chondrocytes in the FC pad. In the high-power views of the ventral joint with the FC pad, O-diet rabbits exhibit numerous apoptotic chondrocytes vs U-diet rabbits (red arrows).

View larger version (139K): [in this window] [in a new window]   Fig. 8. TMJ apoptosis. Coronal sections (6 µm) of middle joint sites from U-diet (A) and O-diet (B) 4-month old subadults were tunel stained to identify cellular apoptosis in articular cartilage. In high-power views of the articular surface and subchondral bone, O-diet rabbits exhibit elevated chondrocyte apoptosis vs U-diet rabbits (red

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