FIELD-EMISSION SEM, CONVENTIONAL TEM AND HVTEM STUDY OF SUBMANDIBULAR-GLAND IN PRENATAL AND POSTNATAL AGING MOUSE

The development of acinar and ductal cells of the mouse submandibular gland was studied using field emission SEM, conventional TEM and HVTEM methods. The specimens, at 15 and 18 days of gestation and 1, 3, 7, 1 4, 21, 30, 90 and 180 postnatal days were fixed in 2.5% glutaraldehyde solution in 0.1M sodium phosphate buffer (pH 7.3). At 15 and 18 days of gestation, the structure of mouse submandibular gland contains acin ar and ductal cells in proliferation. The cytoplasmic organelles such as mitochondria, granular endoplasmic reticulum and Golgi apparatuses ale scattered in the cytoplasm. At 18 prenatal days only several acina r cells present immature secretory granules in the apical portion. In this stage the acinar and ductal cells are enveloped by bundles of fin e collagen fibrils disposed in several directions. There are also nume rous capillaries located closely to the acinar cell membranes. In the aging stages of 1, 3, 7, 14, 21, and 30 postnatal days, the histo-diff erentiation of acinar, intercalated and ductal cell components are obs erved. At newborn day one the cytoplasmic organelles start to place th emselves around the nucleus. Several immature secretory granules are o bserved at day one, however, they increase in the aging days. At postn atal day 30, the cytoplasms of acinar and ductal cells are filled with a large number of secretory granules of different sizes. The stacks o f granular endoplasmic reticulum and Golgi apparatus and some vesicles and free ribossomes are noted. The intercellular membranes are attach ed by desmosomes and cytoplasmic interdigitations. The luminal surface shows several small projections of microvilli. An electron-dense line of basement membranes followed by fine collagen fibrils are recognize d. Delicate capillaries are found in the outer surface of acinar cells . At postnatal day 90 and 180 the acinar, intercalated and striated du ctal cells reveal numerous secretory granules in the apical portion. T he acinar cells showed basal nuclei and the parallel arrangement of gr anular endoplasmic reticulum. The mitochondria are located at the base of ductal cells showing a typical pattern of cristae. In these stages the intercellular digitations of cytoplasmic protrusions and desmosom es are also noted. The cytoplasm of myoepithelial cells are seen along the cell membranes. The spongy-like structures constituting the basem ent membrane are followed by bundles of fine collagen fibers.