Newly developed morphological techniques will be applied for the first time to the study of the normal osteogenic mechanisms in growth plate cartilage. These studies are designed first to increase the understanding of complex cellular interactions associated with metaphyseal vascular penetration into the distal growth plate and subsequently to increase the understanding of the causes of the failure of osteogenesis in a group of over 50 orthopedic diseases, classified as the osteochondroses, that affect young and adolescent children. Using morphological criteria from time lapse cinematography, lectin-binding histochemistry, and improved chemical fixation and serial section microtomy for electron microscopy, it is proposed: 1. To test the hypothesis that for most of its life the terminal hypertrophic chondrocyte is metabolically active in preparing the matrix for vascular penetration; however, ultimately each terminal hypertrophic chondrocyte condenses into a dark cell which rests on the last transverse septum and dies a programmed cellular death by apoptosis. It is hypothesized that condensation is of very short real time duration in the total life of the terminal hypertrophic chondrocyte. Its real time duration will be estimated both with time lapse cinematography in an organ culture system and with morphometric methods modelled after cell cycle techniques. 2. To use the sequence of morphological changes of hypertrophic cell ultrastructure as an internal sequencing time standard by which to study cellular fluxes at the chondro-osseous junction. It is hypothesized that platelets, monocytes, mononuclear phagocytes, and extensions of osteoclasts precede vascular endothelial cells into the pericellular space surrounding terminal hypertrophic chondrocytes. 3. To analyze matrix and chondrocytic lectin-binding glycoconjugates in the distal hypertrophic cell zone. It is hypothesized that changes in glycoconjugates relfect a reorganization of macromolecular components of the pericellular matrix prior to capillary penetration which results both in the clearance of matrix and cellular debris, and in the creation of a suitable substrate for the attachment of migrating endothelial cells. In addition, it is proposed to use lectin-binding histochemistry at both the light and electron microscopical levels to test the hypothesis that plasma membrane changes of the terminal hypertrophic chondrocyte allow its recognition by mononuclear macrophages.
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