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Biomedical subjects

A Nanci

Publications and source records attributed to A Nanci.

96 records · Page 6Linked to original sources
PubMed1983

Selachian tooth development: III. Ultrastructural features of secretory amelogenesis in Squalus acanthias.

Ultrastructural features of secretory amelogenesis during selachian tooth development show several similarities to mammalian amelogenesis. However, the following critical differences were noticed: 1) subcellular organelles associated with merocrine-type protein synthesis and secretion were located in both the infranuclear as well as supranuclear regions of the selachian ameloblasts; 2) no evidence for Tomes process formation was found; 3) the basal lamina was not removed during epithelial differentiation into ameloblasts in the selachian model, and the structural features of the basal lamina were significantly altered during amelogenesis in rows III, IV, and VI; and 4) no dentine-enameloid junction was detected. It is suggested that enameloid is an extracellular matrix which is derived from the selachian inner enamel epithelium and appears to be secreted from both the lateral and apical surfaces of ameloblasts.

Amelogenesis↗
PubMed1982

Stereo electron microscopy of enamel crystallites.

Stereo microscopy was used to examine enamel crystallites in routine thin sections of rat and Chinese hamster incisors. Freeze-fracture replicas were also made of rat incisor enamel. These studies revealed that enamel crystallites are thin, flat, twisting ribbons of unmeasurable length and uniform width. Images previously interpreted as hexagonal crystallites are due to perspective distortion caused by oblique views along cut segments of these flattened ribbons exaggerated by curling, which occurs at the cut crystallite ends. Images of central crystallite dissolution, resulting from beam sublimation, are due to oblique views of hole-pitted crystallite surfaces. Finally, it was concluded that previous measurements made from two-dimensional images of crystallites in electron micrographs are not reliable.

Animals↗
PubMed1980

Quantitative and ultrastructural changes of peritoneal macrophages in immunized rats after intraperitoneal injection of Novikoff hepatoma.

The response of peritoneal cells to transplantable Novikoff hepatoma was studied in immunized and nonimmunized inbred male SD rats to elucidate the role of macrophages in syngeneic tumor rejection. Specific immunization was induced by double sc challenge with viable tumor cells. Peritoneal cells were harvested by lavage at intervals of 6 hours and 1, 2, 3, 4, and 9 days after ip tumor injection. Some of the lavage fluid was used to determine the total number of cells, and the remainder was prepared for ultrastructural study. Different counts were made at the electron microscope level, and the ultrastructures of macrophages and tumor cells were studied. The results indicated that during the early intervals after tumor injection, the numbers of macrophages and lymphocytes were significantly increased in immunized animals. The mononuclear cells accumulated more slowly in the peritoneal cavities of nonimmunized rats. Morphologic heterogeneity was observed in the macrophage population of immunized rats up to day 4. Concurrent with these changes in macrophages were the decreased mitotic activity and ultrastructural alterations in tumor cells followed by their complete disappearance. In nonimmunized animals tumor cells proliferated actively and by day 9 constituted 85% of the peritoneal population.

Animals↗
PubMedDate not supplied

A review of the study of protein secretion applying the protein A-gold immunocytochemical approach.

Exocrine and endocrine types of secretion were investigated in various cells by applying the protein A-gold immunocytochemical approach. Several proteins secreted by rat pancreatic and parotid acinar cells, mouse ameloblasts, rat pancreatic B cells and lymph-node plasma cells, and frog hepatocytes were studied using specific antibodies. While light microscope immunohistochemistry has allowed for good topographical identification of positive cells in tissues, the protein A-gold approach used at the electron microscope level has demonstrated the presence of specific antigenic sites in particular cellular compartments. All secretory proteins studied were detected in the rough endoplasmic reticulum, the Golgi apparatus, and the secretory granules of the corresponding secreting cells. In addition, some of the proteins were also found in lysosome-like structures. When good ultrastructural preservation of the cellular organelles was achieved, the labeling was revealed with very high resolution and precise localization. In such cases, we found labeling over transitional elements of the endoplasmic reticulum and in smooth vesicles in the Golgi area. The Golgi apparatus was subdivided into three compartments according to differences in labeling: the cisternae on the cisside, those of the trans-side and the trans-most rigid one. Quantitative evaluations of the intensities of labeling have allowed for 1) demonstration of the high specificity of the different labelings; 2) revelation of the existence of a gradient of increasing intensity that follows precisely the progress of the proteins along their secretory pathway; and 3) identification of intracellular sites where increments of protein antigenicity occur. Furthermore, they have revealed the existence of alterations in protein processing that occurred under experimental and pathological conditions. Double-labeling approaches were performed to demonstrate two different antigenic sites on the same tissue section by applying protein A-gold complexes formed by gold particles of different sizes. Protein A-gold immunocytochemistry has also been combined with cytochemical and radioautographic techniques. This review thus demonstrates that high-resolution quantitative immunocytochemistry can contribute significantly to the investigation of the intracellular processing of secretory proteins. It also illustrates the potential and versatility of the protein A-gold technique, which in combination with other procedures constitutes a powerful method in cell biology.

Ameloblasts↗
PubMedDate not supplied

Biomaterials and biomechanics of oral and maxillofacial implants: current status and future developments.

Research in biomaterials and biomechanics has fueled a large part of the significant revolution associated with osseointegrated implants. Additional key areas that may become even more important--such as guided tissue regeneration, growth factors, and tissue engineering--could not be included in this review because of space limitations. All of this work will no doubt continue unabated; indeed, it is probably even accelerating as more clinical applications are found for implant technology and related therapies. An excellent overall summary of oral biology and dental implants recently appeared in a dedicated issue of Advances in Dental Research. Many advances have been made in the understanding of events at the interface between bone and implants and in developing methods for controlling these events. However, several important questions still remain. What is the relationship between tissue structure, matrix composition, and biomechanical properties of the interface? Do surface modifications alter the interfacial tissue structure and composition and the rate at which it forms? If surface modifications change the initial interface structure and composition, are these changes retained? Do surface modifications enhance biomechanical properties of the interface? As current understanding of the bone-implant interface progresses, so will development of proactive implants that can help promote desired outcomes. However, in the midst of the excitement born out of this activity, it is necessary to remember that the needs of the patient must remain paramount. It is also worth noting another as-yet unsatisfied need. With all of the new developments, continuing education of clinicians in the expert use of all of these research advances is needed. For example, in the area of biomechanical treatment planning, there are still no well-accepted biomaterials/biomechanics "building codes" that can be passed on to clinicians. Also, there are no readily available treatment-planning tools that clinicians can use to explore "what-if" scenarios and other design calculations of the sort done in modern engineering. No doubt such approaches could be developed based on materials already in the literature, but unfortunately much of what is done now by clinicians remains empirical. A worthwhile task for the future is to find ways to more effectively deliver products of research into the hands of clinicians.

Biocompatible Materials↗