Low temperature ultramicroincineration of thin-sectioned tissue

Plasma etching and ashing: a technique for demonstrating internal structures of helminths using scanning electron microscopy

Plasma etching and ashing for demonstrating the three-dimensional ultrastructure of the internal organs of helminths is described. Adult worms of the cestode Caryophyllaeides fennica were dehydrated through an ethanol series, critical point dried (Polaron E3000) and sputter coated with 60% gold-palladium (Polaron E5100) and glued to a standard scanning electron microscope (SEM) stub positioned as required for ashing. After initial SEM viewing of worm surfaces for orientation, stubs were placed individually in the reactor chamber of a PT7150 plasma etching and ashing machine. Worms were exposed to a radio frequency (RF) potential in a low pressure (0.2 mbar) oxygen atmosphere at room temperature. The oxidation process was controlled by varying the times of exposure to the RF potential between 2 to 30 min, depending on the depth of surface tissue to be removed to expose target organs or tissues. After each exposure the oxidized layer was blown from the surface with compressed air, the specimen sputter-coated, and viewed by SEM. The procedure was repeated as necessary, to progressively expose successive layers. Fine details of organs, cells within, and cell contents were revealed. Ashing has the advantage of providing three dimensional images of the arrangement of organs that are impossible to visualize by any other procedure, for example facilitating testes counts in cestodes. Both freshly-fixed and long-term stored helminths can be ashed. Ashing times to obtain the desired results were determined by trial so that some duplicate material was needed.

Histochemical studies of Ca-ATPase, succinate and NAD+-dependent isocitrate dehydrogenases in the shell gland of laying Japanese quails: with special reference to calcium-transporting cells

In order to elucidate the problem of which cells are involved in calcium transport and to estimate the role of mitochondria in calcium transport in the avian shell gland, the fine structure and the Ca-ATPase, succinate dehydrogenase (SDH) and nicotinamide adenine dinucleotide (NAD+)-dependent isocitrate dehydrogenase (NAD+-ICDH) activity of the shell gland of egg-laying Japanese quails were examined. The surface epithelial cells, consisting of ciliated cells with cilia and microvilli and non-ciliated cells with microvilli, had many large and electron-dense granules. The tubular-gland cells occupied the proprial layer and lacked secretory granules. When an egg was in the shell gland, the well-developed mitochondria of tubular-gland cells characteristically tended to accumulate in the apical cytoplasm, while they were scattered throughout the cytoplasm when an egg was not in the shell gland. Intense Ca-ATPase activity was found on the microvilli of tubular-gland cells, and moderate activity was found on the lateral-cell surface. In the surface epithelial cells, the basolateral cell surface showed moderate enzymatic activity. Both SDH and NAD+-ICDH activity were found in tubular-gland cells when an egg was in the shell gland. These results strongly suggest that calcium for eggshell calcification is actively transported by the tubular-gland (depending on Ca-ATPase activity) and that the mitochondria of gland cells may play an important role in this process as an energy source.

Radio frequency glow discharge and solid-phase lactoperoxidase-glucose oxidase beads as methods for etching ultra-thin plastic sections for immunoelectron microscopy

Etching techniques to prepare ultra-thin sections for immunoelectron microscopy have incorporated a variety of reagents to expose antigenic sites. In this paper involving 2 techniques for surface etching prior to immunoelectron microscopy, radio frequency glow discharge ( RFGD ) and solid-phase lactoperoxidase-glucose oxidase beads ( Enzymobeads ) are compared to conventional peroxide etching techniques. Measuring such parameters as intensity of granule disposition and titers of antibody resulting in detectable staining. RFGD and Enzymobeads were both superior to the conventional peroxide methodology. Non-specific absorption by ferritin under the conditions utilized was not a problem with Enzymobeads or RFGD method. In addition, RFGD may be useful in situations where peroxide susceptible antigens are under study.

Ultrastructural comparison of ion beam and radiofrequency plasma etching effects on biological tissue sections

Three dry etching techniques (Ar+ ion beam, O2+ ion beam, O2 radiofrequency electrodeless discharge) were compared with respect to preferential etching and damage to the ultrastructure of glutaraldehyde-fixed Epon-embedded frog skeletal muscle sections. SEM and TEM studies were performed on both unstained and stained (osmium tetroxide, uranyl acetate) sections. Etching effects were observed to differ for the various ion beam or plasma etching techniques. Whereas selective retention of electron dense structures (e.g. Z lines, nuclear heterochromatin) was observed for oxygen plasma etching, preferential etching of these components was observed using O2+ ion beam bombardment. Selectively etched Z lines and etch-resistant nucleoli were observed for both reactive (O2+) and inert (Ar+) ion beam sputtering after sufficiently high ion doses. The above suggest that selective etching under keV ion beam irradiation is related more to physical sputtering processes (momentum transfer) than to the chemical reactivity of the incident ion. Heavy metal post-fixation and staining had no qualitative effect on the nature of the selective etching phenomena. The above findings are significant in that they potentially influence both electron and ion microprobe measurements of etched biological specimens.

Ultrastructural and cytochemical aspects of the initial phases of an experimental cutaneous calcinosis (calcergy) in the rat

In rats a subcutaneous injection of KMnO4 leads to the calcification of the connective tissue. During mineral deposition, both intra- and extracellular changes are observed in the connective tissue. The intracellular phase is characterized by the formation of intramitochondrial granules and cytoplasmic vesicles, both in fibroblastic and extrinsic cells. In the extracellular phase, numerous heterogeneous matrix vesicles appear in the extracellular matrix. At the same time, globular particles which are resistant to microincineration, are observed between the collagen fibrils. The mineralization of the extracellular matrix takes place in two stages. The first stage comprises the appearance of needle-like structures and round aggregates. The needle-like structures are observed occasionally in the matrix vesicles and often in the extracellular matrix where they appear isolated or diverging from a central point. The round aggregates, composed of dense particles, are seen in the ground substance between the collagen fibrils. The second stage is characterized by a progressive mineralization of the collagen fibrils and the elastic fibers, without formation of extended calcified plaques.

Ultrastructure of cel organelles by scanning electron microscopy of thick sections surface-etched by an oxygen plasma

Kidney tissue double fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin by standard techniques used for transmission electron microscopy was cut into section 1 micron or more thick and surface-etched by an oxygen plasma. Etching caused ash residues (possibly composed partly or organo-metallic complexes) of membranes and other etch resistant cell components to emerge as recognizable structures projecting upward from the surrounding embedment which was combusted and removed as volatile products. using the secondary electron mode for image formation, structural features of cells which could be imaged with clarity with the scanning electron microscopy included: profiles of peripheral and in-folded plasma membranes, the nuclear envelope and profiles of cut mitochondrial matrix granules, cristae and the outer limiting membranes. Resolution was better than that obtainable from most other methods of specimen preparation currently being used in scanning electron microscopy for viewing the internal structures of cells or organelles in bulk samples of tissue.

X-ray microanalysis of epon sections after oxygen plasma microincineration

Dark-gold sections of osmium tetroxide-fixed, Epon-embedded brown adipose tissue before and after low-temperature oxygen plasma microincineration were examined using a high-resolution scanning transmission electron microscope and an energy-dispersive X-ray spectrometer. Microincineration produced ash patterns which were free of organic matrix, chlorine (from the Epon) and probably osmium (from the fixative). X-ray sensitivity was improved by a factor of 2-4 owing to decreased background, and sulphur, calcium and probably phosphorus were detected in the ash. Fidelity of the ash patterns permitted microanalytical spatial resolution of 0.1 micrometer or better. Oxygen plasma microincineration is thus shown to offer advantages for high resolution X-ray microanalysis of conventionally sectioned biological material. Its future application to shock-frozen, frozen-dried, unstained sections is indicated.

The ulstrastructure of the extracellular phase of bone as observed in frozen thin sections

The fine structure of the extracellular phase of avian medullary bone and embryonic chick femur was examined in thin sections prepared by ultracryotomy and ultramicroincineration. Since contact with solutions was completely avoided, little or no loss or dislocation of mineral constituents could occur. Amorphous bone mineral (ABM) was present in two forms: as 15-30 nm spheres and as a structure-free haze. Removal of all organic material by low temperature ashing left the ABM intact. Crystals were usually associated with the ABM. In newly ossifying regions clusters or nodules of randomly oriented crystals and ABM appeared to coalesce when they reached approximately 1 micron in diameter. In highly calcified regions crystals appeared to be oriented along collagen fibers. ABM did not appear to be associated with collagen. Unmineralized collagen was visible in osteoid after staining with dry OsO4 vapor and it appeared to be diverted around nodules. Structures which resembled matrix vesicles were present. Selected area electron diffraction patterns indicated the presence of hydroxyapatite.

Matrix vesicles in newly synthesizing bone observed after ultracryotomy and ultramicroincineration

Matrix vesicles were observed in femurs of 8-day-old chick embryos prepared by ultracryotomy. Some of the sections were subjected to ultramicroincineration. The unfixed tissues never came into contact with solutions, and thereby artifacts due to dissolution, redistribution, or rearrangement of the mineral constituents were avoided. In the osteoid, electron dense objects with the size and appearance of matrix vesicles were seen, although limiting membranes were not visible. After ultramicroincineration the vesicles were observed to contain small crystals and a less dense amorphous mineral material which may te the precursor of bone mineral. In addition, a ring of ash enclosed the crystalline and amorphous mineral and appeared to occupy the position of the vesicle membrane as seen in conventionally prepared material.

Ultrastructural observations of amorphous bone mineral in avian bone

Mineral from medullary bone of three avian species was examined with the electron microscope in order to clarify the ultrastructure of amorphous bone mineral (ABM) in a mineralized tissue. Powders from freeze-dried bone revealed bone mineral with morphology and behavior identical to synthetic amorphous calcium phosphate (ACP). These powders exhibited spherically shaped particles 180--400 A in diameter with uniform electron density when viewed at low beam intensity. Thin sections of embedded freeze-dried bone also revealed spherically shaped particles 100--350 A in diameter with electron beam sensitivity characteristic of ACP. Regions of bone mineral with irregular outline and morphology were observed which closely resemble the discoidal form of synthetic ACP. More electron-dense spherical particles (150 A in diameter) could be seen budding from these regions. Some of these buds exhibited electronlucent centers characteristic of AMB. The inorganic nature of these features of bone mineral was confirmed using ultramicroincineration. Preliminary exploration of a freeze-substitution technique showed spherical bone mineral particles which were similar in morphology to those observed in freeze-dried samples. A limited degree of preservation of cellular material was observed using this freeze-substitution technique.