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Chondrocyte Proliferation of the Cranial Base Cartilage upon in vivo Mechanical Stresses

Skeletal Tissue Engineering Laboratory, Rm 237, Department of Orthodontics and Bioengineering, Univ. of Illinois at Chicago MC 841, 801 South Paulina Street, Chicago, IL 60612-7211, USA;

View larger version (17K): [in a new window]   Figure 1. Structure of the rabbit cranial base cartilage and force waveforms delivered to the rabbit skull. (A) Schematic diagram of the rabbit cranial base cartilage (CBC) or the spheno-occipital synchondrosis. The horizontal arrow indicates 2-Newton tensile forces applied to the maxillary incisors. The CBC, schematically represented as a rectangle, is located between the sphenoid and occipital bones. (B,C) Traces of exogenous forces with the same peak magnitude of 2 Newtons but with two different waveforms: static force (B) and cyclic force (C). The static force failed to induce any substantial oscillation in force magnitude over the representative 10-second time course (B). In contrast, the cyclic force of the same peak magnitude oscillated at 1 cycle per sec, totaling 10 cycles in the representative 10-second time course (C).

View larger version (150K): [in a new window]   Figure 2. BrdU labeling of growth plate chondrocytes. Representative photomicrographs of chondrocyte proliferation labeled with bromodeoxyuridine (BrdU) in the proliferating zones of the cranial base cartilage (CBC). (A) Negative control (no BrdU antibody). (B,C,D) Samples treated with BrdU antibodies. B, sham control; C, static force; D, cyclic force. There are marked increases in BrdU-labeled proliferating chondrocytes in association with cyclic force (D), in comparison with natural chondral growth (B) and static force (C). Arrows indicate the nuclei of proliferating chondrocytes. Scale bar: 40 µm.

View larger version (99K): [in a new window]   Figure 3. Proliferating zone area of sham control and mechanical stimulation. Representative photomicrographs of the cranial base cartilage (CBC) showing sham control (A,A'), static force (B,B'), and cyclic force (C,C'). A, B, and C were stained with hematoxylin and eosin; A', B', and C' were stained with safranin O and fast green. The total proliferating zone area treated with cyclic forces (C,C'), manually isolated by computerized image analysis, showed marked increase in comparison with static forces (B,B') and sham controls (A,A'). Reaction to safranin O confirmed the presence of abundant chondroitin-sulfate and keratan-sulfate binding proteoglycans, most likely aggrecan, in the cartilage matrix. Scale bar: 150 µm.

View larger version (27K): [in a new window]   Figure 4. Quantification of BrdU labeling and histomorphometry of the proliferating zone. (A) The average BrdU labeling index of the proliferating zone treated with cyclic force (N = 7) was significantly greater than that of static force (N = 6) (p < 0.05) and sham control (N = 7) (p < 0.01). (B) The average total area of the proliferating zone treated with cyclic force was significantly greater than those of static force (p < 0.05) and sham control (p < 0.01).