Animals ; Cytoplasm ; ultrastructure ; Fibroblasts ; ultrastructure ; Fractures, Bone ; pathology ; Microscopy, Electron ; Osteoblasts ; ultrastructure ; Rabbits ; Wound Healing

The normal lumbar intervertebral discs of rat, rabbit and human (fetal and adult) were studied under transmission electron microscope. In all the specimens the following findings could be observed. The annulus fibrosus was composed of fibrocartilage. However, the cells in the lacunae of the fibrocartilage might show changes in form with the location of the lacunae. The cells in those lacunae on the periphery of the annulus became elongated and lost their scalloped cytoplasmic membrane, thus resembled fibroblasts. On the contrary, the cells in those lacunae in the central portion of the annulus revealed characteristics of the notochordal cells, with pyknosis of nucleus and aggregation of glycogen and fat droplets in the cytoplasm. Consequently the annulus fibrosus exhibited a transition of their cellular components. Elastic fibers could be found in the annulus. Nucleus pulposus contained notochordal cells in a loose matrix. The notochordal cells might exist singly or in clusters and in their cytoplasm there were many vacuoles and aggregates of glycogen and microfilaments.

An experimental study was carried out on the isolated bone cells, from the embryonic calvarium of Sprague-Dawley rats which were taken out in vitro culture in the later period of gestation. Observation of the early stage of culture was carried out with phase contrast microscope, H. E. staining and AcP and AlP technique. It was found that both the osteogenic cells of the cambium layer of the periosteum and the undifferentiated cells from the bone marrow could develop into large squamous-shaped cells. These cells possessed many processes connected with the adjacent cells and stained light red color with Sirius Red but revealed no birefringency under polarized microscope. This indicates that these cells are precursors of collagen formation. The negative reaction with the alkaline phosphatase staining pointed out that these cells still belong to the osteogenic cells.

OBJECTIVE: To investigate ultrastructurally into traumatic avascular necrosis of femoral head. METHODS: Femoral heads were procured during endoprosthetic replacement for 8 cases of intracapsular fracture of femoral neck, which had been subjected to internal fixation and developed Stage II avascular necrosis. The specimens were processed and studied under transmission electron microscope. RESULTS: In the normal bone tissues of the avascular necrotic femoral heads, the collagen fibrils constituting the collagen bundles of the bone matrix were of uniform diameter, and were regularly arrayed with orientation. In the necrotic bone tissues of the avascular femoral heads, the collagen fibrils were of unequal diameter, and were haphazardly arrayed without orientation. From the trabeculae of the avascular femoral heads emerged three different conditions of osteocytes: (1) In the trabeculae of normal bone tissues, the osteocytes belonged to both degenerative phase and formative phase osteocytes with the latter showing signs of degeneration; (2) In the necrotic trabeculae, the osteocytes perished leaving behind empty lacunae; (3) Over the trabeculae of the interface region could be discerned many active osteogenic cells, which were on their way of transformation into osteoblasts. In the trabeculae here, the osteocytes belonged to both formative phase and degenerative phase osteocytes. CONCLUSIONS: These results suggest that in the femoral heads with traumatic avascular necrosis, there is active osteogenetic activity around the necrotic bone tissues, amply implying a local reparative response following partial bone necrosis.

OBJECTIVE: To investigate further into the osteogenic potential of rabbit dermal fibroblasts with scanning electron microscope. METHODS: Split-thickness rabbit skin was processed into small chips that were cultured in vitro and then subjected to scanning electron microscopic study. RESULTS: The fibroblasts swam out from the skin chips and they increased in number rapidly and became confluent. The cells exhibited squamous configuration, possessing arboreal bifurcation and forming multi-layer structure. The fibroblasts then excreted numerous minute granules, heaping up on and around the cells. Thenceforth emerged on the cell surface fine needle-like crystals, that agglomerated with the granules to form nodules. The fibroblasts orientated themselves in a radiating pattern around the large nodules. Neighboring nodules could be linked up into trabecular structures. CONCLUSIONS: Sequence of events of new bone formation by rabbit dermal fibroblasts cultured in vitro is fully depicted and confirmed.

OBJECTIVE: To analyze the expression of procollagen gene in fracture callus, and to search for the technique of in situ hybridization for undecalcified skeletal tissue. METHODS: In situ hybridization of procollagen gene expression was performed on the undecalcified cryosections of rat fracture callus at 7, 14, and 28 d. RESULTS: The hybridization signals achieved were clear and easy to be localized with high specificity. On the 7th day, the expressions of pro alpha1 (III) in fibroblasts and some chondrocyte-like cells were dominant; and at the end of second week high expression of type-II procollagen mRNA was observed in chondrocytes. At the end of fourth week, the cartilaginous callus was almost all replaced by woven bone tissue, and some type-I procollagen mRNA positive osteoblasts and hypertrophic chondrocytes were found scattering in the woven bone and remnants of cartilaginous callus. CONCLUSIONS: The modified method employed in this study is easier, quicker, and more sensitive with high specificity than the conventional tec hnique for in situ hybridization of procollagen gene expression of decalcified rat fracture callus. The phenomenon of shared phenotype expression, which was demonstrated among cells engaged in fracture healing, indicates an important approach to reveal the mechanism of the origin, differentiation, and orientation of cells.