The ultrastructure of the blood capillaries in the mouse thyroid gland

Summary In the mouse thyroid gland the endothelium lining the blood capillaries is separated from the epithelial cells by a periendothelial space composed of three layers. Two of these are rather dense and localized close to the epithelium and endothelium, respectively. The third layer, interposed between the two dense layers, has a very low density. The dense layers, having each a thickness of 400–500 Å, show at high magnification in some places a lamellated structure. The middle layer varies in thickness and contains sometimes aggregates of a homogeneous material, circular bodies bordered by a membrane and, in single cases, fibrillar structures.The major part of the endothelial wall is very thin, only 200–600 Å. Within these thin parts discontinuities are observed, the endothelial cytoplasm being replaced by a more or less distinct membrane, about 50 Å thick. The dimension of the discontinuities is about 400 Å. The observations made are discussed.     

Ultrastructure of the human submaxillary gland

Summary Myoepithelial cells in the human submaxillary gland are stellate in form, with long, tapering processes. They are interposed between the base of the secretory cells and the basement membrane, and are bound to the secretory cells by desmosomes. Their cytoplasm contains numerous myofilaments measuring approximately 40 Å in diameter, which frequently aggregate to form structures similar to the dark bodies seen in smooth muscle cells. The myofilaments are anchored to the plasma membrane by attachment devices. The myoepithelial cells are often accompanied by cells which have a similar shape, but possess an extremely electron-lucent cytoplasm that contains almost no organelles or inclusions. Electron microscopical observations indicate that these cells, termed clear cells, are transformed directly into myoepithelium, since all morphological intergrades between the two cell types have been recognized.This work was supported in part by a grant from the Henry Spenadel Trust. The technical assistance of Mr. Roy R. Keppie and Mrs. Mona Brandreth is gratefully acknowledged.     

Ultrastructure of the ferret sublingual gland

The sublingual glands of 2 male and 2 female adult ferrets were examined using electron microscopy. The secretory end piece consisted of mucous tubules, serous and mixed acini. The mucous cells showed two different types of granules. The serous cells contained electron-dense secretory granules. The duct system entirely comprised excretory ducts.     

Estimation of thyroid gland activity in the Snell dwarf mouse by ultrastructural observation of the thyroid gland, measurement of plasma thyroxine concentration and thyroid hormone binding capacity

An ultrastructural study of the thyroid gland of the Snell dwarf mouse showed cellular activity to be very low. Follicle cell diameters were significantly lower than in controls whilst the nucleocytoplasmic ratio was significantly higher. The observed cellular activity of the thyroid cells was associated with circulating levels of thyroxine which were found to be significantly lower than in controls. Measurement of the free thyroxine index showed very little free hormone available for tissue uptake. No differences in thyroid function due to age or sex in the dwarf mice were seen. Possible endocrine imbalances contributing to the low thyroid activity in the Snell dwarf mouse are discussed.     

Long-term preservation of freeze-dried mouse spermatozoa

Many genetically engineered mice strains have been generated worldwide and sperm preservation is a valuable method for storing these strains as genetic resources. Freeze-drying is a useful sperm preservation method because it requires neither liquid nitrogen nor dry ice for preservation and transportation. We report here successful long-term preservation at 4 °C of mouse spermatozoa freeze-dried using a simple buffer solution (10mM Tris, 1mM EDTA, pH 8.0). Offspring with fertility were obtained from oocytes fertilized with freeze-dried spermatozoa from C57BL/6 and B6D2F1 mouse strains stored at 4 °C for 3 years. This freeze-drying method is a safe and economical tool for the biobanking of valuable mouse strains.     

Ultrastructure of the submandibular gland in the rabbit

The secretory endpieces of the rabbit submandibular gland are unusual in that they consist of seromucous acini (not demilunes) that empty into serous tubules that in turn drain into intercalated ducts. Seromucous granules consist of a moderately dense spherule in a fibrillogranular matrix. Serous granules contain a feltwork of filaments, which are liberated as a tangled skein during exocytosis. Peculiar granulated cells that have secretory granules of complex morphology are present at each end of the serous tubules. Intercalated ducts are, cytologically speaking, relatively simple, but the duct cells may contain a few oblong secretory granules. Striated ducts are typical in structure, although postfixation with ferrocyanide-reduced osmium reveals significant amounts of glycogen in the basal processes. Modified mitochondria are present in striated duct cells, but their frequency varies from rabbit to rabbit. Such mitochondria contain either an array of parallel, rigid cristae linked by intermembranous bridges, or a bundle of helical filaments within an expanded crista. Interspersed with the striated duct cells, especially near the duct origin, are some highly vacuolated cells with sparse mitochondria. Excretory ducts consisting of stratified columnar (sometimes pseudostratified) epithelium often show bleb formation of the luminal surface of the tall cells.     

Quantitative electron microscopic autoradiography on the mouse thyroid gland after administration of 3H-L-DOPA

Summary The cellular and subcellular distribution of radioactivity in the mouse thyroid gland different times (20 min — 8 hours) after intravenous administration of ³H-L-DOPA was studied by means of quantitative electron microscopic autoradiography.High concentrations of autoradiographic silver grains occur over parafollicular cells and adrenergic nerves while the labelling of follicular cells and lumina is low or absent and similar to the labelling of connective tissue cells at all observation times.Over the parafollicular cells high levels of radioactivity can be recorded already 20 min after administration of the labelled amino acid. The grain counts are highest at 1 hour and decrease then at 2.5 and 8 hours.The intracellular distribution of label is similar at all observation times; thus, the concentration of silver grains over the typical cytoplasmic granules of the parafollicular cells is 4–5 times higher compared to the concentration over the remainder of the cytoplasm and the nucleus.Treatment with a decarboxylase inhibitor prior to the injection of ³H-L-DOPA results in a low and uniform labelling of all thyroid cells. This finding, taken together with the observation that also pretreatment with reserpine abolishes the autoradiographic reaction over the cytoplasmic granules, gives strong support to the idea that the great majority of silver grains observed over parafollicular cells represents dopamine formed by decarboxylation of the labelled precursor.This study was supported by grant K71-12X-3352-01 from the Swedish Medical Research Council. The author wishes to express his gratitude to Mrs. Gunnel Bokhede and Miss Dala Sjögren for expert technical assistance.