Ultrastructural cytochemistry of the secretory granules of the hamster submandibular gland

Summary The ultrastructure and cytochemistry of the secretory granules of the male hamster submandibular salivary gland were studied. After fixation in glutaraldehyde followed by osmium tetroxide the granules exhibit a characteristic bipartite substructure, with an electron lucid crescenteric rim and a more dense central core. A differentiation into two regions of the granules could also be visualized in specimens primarily fixed in Millonig's osmium tetroxide or in potassium permanganate. The electron lucid peripheral portion of the membrane bounded secretory granules further displays a strong positive reaction after staining of ultrathin sections with the periodic acid-chromic acid-(PA-CrA)-silver technique. The strong periodate reactivity of the rim relative to the core, suggests a difference in mucin composition of the two granule regions. With the PA-CrA-silver staining technique a positive reaction was also observed within the Golgi apparatus of the acinar cells.     

Osmium dependent argentaffin staining of lysosomes

Summary Lysosomes stain with the argentaffin reaction after fixation with glutaraldehyde followed by osmium tetroxide. The reaction works well both at the level of the light and electron microscope. Control experiments show that this argentaffinity is caused by reduced osmium tetroxide. No staining could be observed in freeze-dried material, in tissues fixed only with glutaraldehyde, or after bleaching of the sections with hydrogen peroxide solutions. In the electron microscope, the population of lysosomes appears heterogeneous as related to the density of silver deposits over the organelles. No correlation is found between size and argentaffinity of lysosomes. X-ray microanalysis of sections from glutaraldehyde/osmium tetroxide fixed material reveals significantly higher amounts of osmium in lysosomes, as compared to other cell organelles (e.g. peroxisomes or mitochondria). A significant peak for silver is observed in lysosomes after treatment of the sections with ammoniacal silver solution, whereas the signal for osmium is reduced. Amounts of sulphur are too low to be detected in lysosomes. It is concluded that argentaffin staining of lysosomes is an osmium dependent reaction.Parts of these results have been presented as a poster during the 20th Congress of Electron Microscopy, joint session of the Austrian Society of Electron Microscopy and the German Society of Electron Microscopy, August 23–28, 1981, Innsbruck, Austria     

A simple impregnation technique for thin and semithin enterochromaffin cells in sections

Summary Constant, intense and precise impregnation of enterochromaffin (EC) cells was achieved simply by floating thin or semithin sections of gut mucosa, fixed in osmium tetroxide or in glutaraldehyde with postfixation in osmium, on a silver nitrate or proteinate solution. EC cells alone showed impregnation in the light microscope. In the electron microscope, impregnation affected not only the secretory granules of EC cells but also, although much more faintly, those of other, non-EC cells (D, X, D₁, G and other cells). Lysosomes also showed partial or total reactivity. Oxidation reduced but did not entirely suppress EC cell staining and had no effect on non-EC endocrine cell staining. Since the reaction did not occur with glutaraldehyde alone, osmium appeared to be a crucial component of the process. These findings should be borne in mind in applying Thiery's method for vicinal glycol groups to the type of study material used in these experiments.     

A simple impregnation technique for thin and semithin enterochromaffin cells in sections

Constant, intense and precise impregnation of enterochromaffin (EC) cells was achieved simply by floating thin or semithin sections of gut mucosa, fixed in osmium tetroxide or in glutaraldehyde with postfixation in osmium, on a silver nitrate or proteinate solution. EC cells alone showed impregnation in the light microscope. In the electron microscope, impregnation affected not only the secretory granules of EC cells but also, although much more faintly, those of other, non-EC cells (D, X, D1, G and other cells). Lysosomes also showed partial or total reactivity. Oxidation reduced but did not entirely suppress EC cell staining and had no effect on non-EC endocrine cell staining. Since the reaction did not occur with glutaraldehyde alone, osmium appeared to be a crucial component of the process. These findings should be borne in mind in applying Thiery's method for vicinal glycol groups to the type of study material used in these experiments.     

THE EFFECTS OF RESERPINE AND HYPOXIA ON THE AMINE-STORING GRANULES OF THE HAMSTER CAROTID BODY

The carotid bodies from control, reserpine-treated, and hypoxia-treated hamsters were fixed with phosphate-buffered glutaraldehyde and osmium tetroxide, s-Collidine-buffered osmium tetroxide, or phosphate-buffered glutaraldehyde followed by potassium dichromate incubation. Following glutaraldehyde-osmium tetroxide fixation no differences in density or population of the electron-opaque granules in the glomus cells of either control or experimental animals were observed. With s-Collidine-buffered osmium tetroxide and the glutaraldehyde-dichromate technique a marked decrease in density without an appreciable reduction in number of granules was noted after reserpine treatment, while in hypoxia-treated hamsters the density and population of the granules were not different from those of the controls. The results indicate that reserpine depletes the amines without granule disappearance and that hypoxia does not affect the amine content of the granules. It is suggested that following glutaraldehyde-osmium tetroxide double fixation, persistence of the density of the granules in reserpine-treated animals is due primarily to the nonamine content, and that the amines in the glomus cells are probably not directly involved in the respiratory reflex.     

Application of silver stains to gastric endocrine cells in plastic sections

Summary A simultaneous light and electron microscopic study of mouse gastric mucosa was made to determine whether the silver nitrate methenamine stain of Duk-Ho Lee could be used to stain gastric endocrine-like cells in plastic embedded tissue. Examination of consecutive thick and thin sections showed that this stain blackened the granules of the predominant type of endocrine-like cell present. Blackening of the granules with silver occured in tissue fixed in osmium tetroxide solution with or without dichromate salt or in tissue fixed in glutaraldehyde then treated with osmium. The intensity of staining was deepest in the osmium-dichromate fixed tissue, but the glutaraldehyde-osmium procedure gave less interference from diffuse silver impregnation and better preservation of detail for electron microscopy.     

Ultrastructural localization of glycogen in the granulocytes of normal rabbit bone marrow.

The glycogen of rabbit granulocytes has been studied in glutaraldehyde and osmium tetroxide fixed bone marrow by the periodic acid-thiocarbohydrazide-silver proteinate procedure (PA-TCH-SP). The PA-TCH-SP procedure involved the staining of intracytoplasmic glycogen more densely than the routine lead citrate staining. The PA-TCH-SP procedure demonstrated the intracytoplasmic glycogen in all three kinds of granulocytes. Though a sequence of intensity was observed in each stage of cell maturation, intracytoplasmic glycogen increased generally in accordance with cell maturation in the granulocytes. Functional significance of the glycogen in the granulocytes was discussed in relation to its staining. A very weak reaction in the granules of the granulocytes was described in relation to their contents.     

Imidazole-buffered osmium tetroxide: an excellent stain for visualization of lipids in transmission electron microscopy

Summary The usefulness of imidazole-buffered osmium tetroxide as a stain for lipids in transmission electron microscopy has been investigated. Rat liver and other tissues were fixed by perfusion with glutaraldehyde and post-fixed with osmium-imidazole and the appearance of lipid droplets was compared with that after post-fixation in unbuffered aqueous osmium tetroxide or an osmium solution buffered otherwise. Prominent electron-opaque staining of lipid droplets and of lipoprotein particles was noted after post-fixation with 2% osmium-imidazole, pH 7.5, for 30 min. The lipid droplets appeared well circumscribed with no evidence of diffusion. In contrast, the intensity of staining was much less and there was some diffusion around lipid droplets in material post-fixed in aqueous or cacodylate-buffered osmium tetroxide. Spot tests on filter paper revealed that unsaturated fatty acids, especially linolenic and linoleic acids reacted more intensely with osmium-imidazole than with aqueous osmium tetroxide. These findings demonstrate that osmium-imidazole provides an excellent stain for lipids in transmission electron microscopy and that most probably it stains lipids with unsaturated fatty acids.     

Ultrastructural localization of glycogen in the granulocytes of normal rabbit bone marrow

Summary The glycogen of rabbit granulocytes has been studied in glutaraldehyde and osmium tetroxide fixed bone marrow by the periodic acid-thiocarbohydrazide-silver proteinate procedure (PA-TCH-SP). The PA-TCH-SP procedure involved the staining of intracytoplasmic glycogen more densely than the routine lead citrate staining. The PA-TCH-SP procedure demonstrated the intracytoplasmic glycogen in all three kinds of granulocytes. Though a sequence of intensity was observed in each stage of cell maturation, intracytoplasmic glycogen increased generally in accordance with cell maturation in the granulocytes. Functional significance of the glycogen in the granulocytes was discussed in relation to its staining. A very weak reaction in the granules of the granulocytes was described in relation to their contents.     

Swelling of golgi apparatus cisternae in monensin-treated tissues is modulated by fixation conditions

Summary Swelling of Golgi apparatus cisternae is reported to be a common response to the ionophore, monensin. However, the amount of swelling depends on fixation, thus raising the question of whether the swelling response is due to monensin or to the fixation protocol. To resolve this problem, maize root cap cells were treated with monensin and then fixed with glutaraldehyde and osmium tetroxide (applied sequentially), osmium tetroxide alone, or aqueous potassium permanganate, or were quick frozen in liquid propane and substituted in acetone-osmium tetroxide. The chemical fixatives (which take minutes to stabilize tissue elements) were judged by comparison with freeze substitution which requires only fractions of a second to stabilize tissue elements. The results verify that monensin causes cisternal swelling and that this swelling is best observed at the ultrastructural level by fixation in glutaraldehyde/osmium tetroxide or by freeze substitution.     

Ultrastructure of the concentric membrane system in Arthrinium aureum

An ultrastructural study was performed on Arthrinium aureum. The fungi were treated with glutaraldehyde and osmium tetroxide fixation. The hypha and conidia has a concentric membrane system which consisted of multiple membranes of a myelinoid appearance, and continued to the conidia and hypha plasma membrane. The fungi were also treated with periodic acid-alkaline bismuth (PABi) staining after glutaraldehyde and osmium tetroxide fixation. PABi positive materials were found on the marginal glycogen granules, the concentric membrane system and the conidia plasma membrane.     

RAPID RELEASE OF THE ZYMOGEN GRANULE PROTEIN BY OSMIUM TETROXIDE AND ITS RETENTION DURING FIXATION BY GLUTARALDEHYDE

Fixation by osmium tetroxide and glutaraldehyde of zymogen granules isolated from rat parotid and pancreas was investigated. Protein determinations showed that osmium tetroxide caused rapid release of most of the soluble protein of the granule during fixation in buffered isotonic sucrose. Such granules when examined in the electron microscope after shadow casting appeared quite flat, indicating that most of the contents had indeed been removed. Numerous damaged membranes of the granules were also observed. In contrast, zymogen granules fixed by glutaraldehyde and shadow cast essentially retained the spherical shape and the protein contents. The application of the shadow-casting technique in quantitative studies on the protein content of zymogen granules is discussed.     

ELECTRON MICROSCOPIC LOCALIZATION OF ACID PHOSPHATASE AND THIAMINE PYROPHOSPHATASE ACTIVITY IN HYPOTHALAMIC NEUROSECRETORY CELLS OF THE RAT

Supraoptic nuclei in the hypothalamus of rats were fixed for the electron microscope by vascular perfusion with solutions of glutaraldehyde followed by post fixation with osmium tetroxide. Cytochemical methods for detection of acid phosphatase and thiamine pyrophosphatase activity have been applied to glutaraldehyde-fixed frozen sections containing the neurosecretory cells. The enzyme activities have been localized to certain Golgi cisternae. Acid phosphatase activity is present in the large (0.4 µ to 1.0 µ) granules or dense bodies which are surrounded by a single limiting membrane; both features characterize these structures as lysosomes. Smaller (0.1 µ) granules also present in the perikarya are generally unreactive towards enzyme activity and resemble in form the neurosecretory granules in the neurohypophysis.     

Spermatogenesis in animals as revealed by electron microscopy

Summary Testes of the pond snail, Cipangopaludina malleata Reeve, were fixed in 1% osmium tetroxide, 3% permanganate, or 4% formaldehyde followed by 1% osmium tetroxide, each being buffered to pH 7.2 with Veronal-acetate or Sörensen's phosphate buffer. On the other hand, testes fixed with 4% formaldehyde adjusted to pH 7.2 with 0.075 M Na-cacodylate were incubated in Novikoff-Goldfischer medium for demonstrating thiamine pyrophosphatase, uridine or inosine diphosphatase, uridine monophosphatase or adenosine triphosphatase. The specimens incubated were postfixed in 1% osmium tetroxide buffered to pH 7.2 with Veronal-acetate buffer. Thin sections of the epoxy Epon resin-embedded tissue were stained either singly with saturated aqueous uranyl acetate or doubly with saturated aqueous uranyl acetate followed by lead citrate.In a concentric lamellar structure consisting of the granular endoplasmic reticulum in the cytoplasm of early atypical spermatids, disappearance of ribosomes attached to the outer surface of cisternae seems to have initiated at the central part of the structure, and the cisterna-attached ribosomes seem to participate in the formation of dense granules appearing in the vesicles representing the endoplasmic reticulum of atypical spermatids.The Golgi apparatus of the atypical spermatids in the advanced stages of development is composed of at least three different layers, the central part consisting of an amorphous material, the following lamellar and vesicular elements, and the peripheral fine vesicles.It has been assumed that the mechanism by which the nucleic acid, especially DNA is converted into the polysaccharide might be attributed to the function of the Golgi apparatus, because the transformation of dense granules into less dense granules as well as diphosphatase activities have been detected within the Golgi apparatus.This study was supported by Grant GM-8327-06 from the United States Public Health Service.     

ULTRASTRUCTURAL LOCALIZATION OF ACID MUCOSUBSTANCES IN THE MOUSE COLON WITH IRON-CONTAINING STAINS

Selective ultrastructural staining of acid mucosubstances in sites containing histochemically identifiable sulfo- and sialomucins has been obtained in fixed cryostat sections with both ferric chloride and colloidal iron solutions. The rectosigmoid region of mouse colon was fixed in glutaraldehyde, formalin, or phosphate-buffered osmium tetroxide, and 40 µ cryostat sections of this material were treated with 0.1 to 0.4% ferric chloride or with a solution of dialyzed ferric chloride, ammonia, and glycerin. Specific staining depended upon the pH of the iron-containing solutions, and the optimal value was found to be approximately 2.0. Specific localization of acid mucosubstances has been noted in intracellular sites, including globules within colonic goblet cells and "deep crypt" mucous cells, small vesicles of the superficial nongoblet epithelial cells, and Golgi lamellae within each of these cell types. Extracellular material, presumed to be acid mucosubstance, was found on the surface of the epithelial microvilli and on the lumenal surface of capillary endothelium. Similar material formed a reticular network surrounding stromal cells, collagen bundles, and various colonic connective tissue elements.     

An improved immunocytochemical method for subcellular localization of serotonin in rat enterochromaffin cells

Serotonin-like immunoreactivity (5-HT-LI) has been localized at the ultrastructural level in enterochromaffin (EC) cells of rat gastrointestinal tract. Ultra-thin sections of tissues embedded in epoxy resin were incubated with 5-HT antisera and antibody binding sites were visualized with protein A-gold. Three different antisera were compared and were shown to require different fixation regimens for optimal preservation of 5-HT-LI. For one antiserum, tissues fixed in glutaraldehyde and osmium tetroxide could be used to demonstrate 5-HT-LI in EC cells. Immunocytochemical localization of 5-HT can thus be performed with good ultrastructural preservation of tissues. Quantitative evaluation of the intracellular distribution of 5-HT-LI was performed on EC cells from antrum, duodenum, and proximal colon, fixed in glutaraldehyde only. In all three locations, the majority of the gold particles (90%) in EC cells were localized over the dense core of the secretory granules, while a minor fraction (10%) were localized in parts of the cytoplasm devoid of granules. In EC cells fixed in glutaraldehyde and post-fixed in osmium tetroxide, 5-HT-LI was reduced by about 85%, although intracellular distribution was essentially the same as in cells fixed in glutaraldehyde alone. The results indicate that 5-HT in EC cells is stored mainly in secretory granules, with a small fraction of 5-HT being localized outside the granules.     

Ultrastructural localization of immunoreactive neurophysins using monoclonal antibodies and protein A-gold

Using three different monoclonal antibodies against rat neurophysins (5), with protein A-gold as immunocytochemical marker (27), the murid hypothalamoneurohy-pophysial system was studied at the ultrastructural level. Postembedding staining was done on epoxy-embedded sections of supraoptic nuclei and posterior pituitaries. Specific immunolabeling of vasopressinergic and oxytocinergic neurosecretory granules was observed in tissues fixed with glutaraldehyde or glutaraldehyde mixtures (containing paraformaldehyde and picric acid), with or without osmium tetroxide postfixation and with or without sodium metaperiodate oxidation. Some autophagic vacuoles containing lysed neurosecretory granules were also neurophysin immunoreactive. Nonspecific background staining was extremely low. An attempt was made to appraise labeling intensities semiquantitatively by counting gold particles in relation to number of secretory granules per axonal varicosity. Immunoreactivity was measurably influenced by the mode of fixation, sodium metaperiodate oxidation, and titer and affinity of the antibody. The protein A-gold technique using monoclonal antibodies against neurophysins provides a superior means of ultrastructural analysis of the hypothalamoneurohypophysial system, both visually and morphometrically.     

ULTRASTRUCTURAL STUDIES OF ABSCISSION IN PHASEOLUS: LOCALIZATION OF PEROXIDASE

Segments of leaf abscission zone tissue of Phaseolus vulgaris L. cv. Red Kidney were fixed in glutaraldehyde, incubated to demonstrate peroxidase activity in medium containing 3,3'-diaminobenzidine (DAB) and postfixed in osmium tetroxide. Electron microscopic observation of treated tissue revealed pronounced deposition of highly electron-opaque material in the form of granules or globules in cell walls, on mitochondrial membranes, associated with rough endoplasmic reticulum and along the plasmalemma and tonoplast. This distribution pattern was typical of both non-treated and ethephon-treated tissue. Ethephon-treated material also contained these granules within cytoplasmic vacuoles. It is suggested that pH of the incubation medium may affect localization sites and that exposure of tissue to light during incubation may modify localization patterns. Differing patterns of distribution of the reaction product in treated and non-treated tissue may reflect changes in membrane permeability and microfibrillar modifications related to ethephon treatment.     

Electron microscopy of cardiac tissue in a primitive vertebrate Myxine glutinosa

Hearts of the Atlantic hagfish, Myxine glutinosa were studied with the electron microscope after prefixation in phosphate buffered glutaraldehyde or buffered formalin and subsequent postifxation in phosphate buffered osmium tetroxide. Epicardial, myocardial and endocardial layers are identified; however the hearts of Myxine lack an extensive capillary system comparable to the coronary vessels of other vertebrate heart tissues. Instead, blood is supplied to cells via an elaborate system of channels which extend between numerous trabeculae that make up the cardiac wall of this organism. Fine structural features of special interest include the presence of numerous dense granules (chromaffin granules) within myofibers and also specific granular cells which lack the contractile elements that are characteristic of both skeletal and cardiac myofibers. Another prominent feature noted includes an elaborate system of tubular invaginations within the subjacent sarcoplasm. These elements appear to be specific for the myofibers. They are continuous with the plasma membrane and project into the peripheral sarcoplasmic matrix. Crystalline inclusions are also observed in the sarcoplasm of the myofibers. These are compared with similar inclusions in other cellular components. The Golgi complex is very extensive in the myofibers of Myxine, and granules of varying sizes and densities often appear in the vicinity of the Golgi saccules. The observations suggest that the numerous vesicles around the Golgi Complex represent intermediate stages in the formation of the chromaffin granules. The structure and function of the extensive tubular invaginations are compared with the transverse tubules reported in several mammalian heart tissues.     

Lipid staining for the electron microscope: a new method.

Tissues fixed in osmium tetroxide or in combined osmium and glutaraldehyde (Hinde), embedded in Spurr's medium, cut at 0-5-I mum and mounted in Farrants' gum medium containing ethyl gallate, show good staining of lipid-contaning structures (droplets of triglyceride, membranes, mitochondria, etc.) in the light microscope. Such preparations show moderate contrast in the electron microscope without further staining. But a specific increase in contrast in lipid-rich structures is obtained by partition of the tissues, before embedding, in 70% ethanol saturated with the monoterpene hydrocarbon myrcene, with or without the addition of 0-I % ethyl gallate, followed by osmium tetroxide. This method will visualize both saturated and unsaturated lipids, including waxes.