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Biomedical subjects

J Appleton

Publications and source records attributed to J Appleton.

At least 37 records · Page 2Linked to original sources
PubMed1992

Dentinogenesis and the calciotraumatic response to the injection of lead or fluoride ions.

A number of ions can disturb the formation of dentine resulting in a calciotraumatic response. The calciotraumatic response following the injection of sodium fluoride was investigated using backscattered electron imaging in the scanning electron microscope and compared with the response to lead acetate. With fluoride, there was formation of a hypermineralized band succeeded by a relatively hypomineralized band, but with lead acetate, only a hypomineralized band was produced. However, there were some differences in the response between the labial and lingual dentine with both ions. In the labial dentine following injection of sodium fluoride, the onset of hypermineralization was less abrupt than in the lingual dentine. Furthermore, the transition from hypermineralization to relative hypomineralization was more abrupt in the labial dentine. Sometimes there was an increased thickness of labial dentine between the hypermineralized layers towards the apex of the tooth and this dentine was less homogeneously mineralized. Normal incremental lines were occasionally seen both labially and lingually. Lead acetate produced a more severe disruption of dentine formation labially than lingually. These differences in response may be related to the pattern of mineralization labially and lingually and to the systemic effects following the injection of sodium fluoride.

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PubMed1991

The effect of lead acetate on dentine formation in the rat.

The intravenous injection of lead acetate produces a response in dentine by formation of the so-called lead line. This is associated with a rapid but temporary rise in serum calcium and phosphorus. Previous studies have suggested that lead replaces calcium and phosphorus in the apatite lattice. In this study the lead line was investigated in the scanning electron microscope using backscattered electron imaging and was shown to consist of continuous hypomineralized interglobular spaces within the dentine. Dentine formation was disrupted for at least a week after injection of lead ions. With energy dispersive analysis by X-rays, no localized concentration of lead was detectable within the 'lead line'. It is suggested that the lead line results from a direct effect of lead on the odontoblasts and other hard tissue-forming cells producing a rapid loss of intracellular calcium temporarily displaced by lead ions and a subsequent disturbance of local calcium metabolism.

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PubMed1988

The ultrastructural distribution of proteoglycans in normal and rachitic growth cartilage from the mandibular condyle of the rat.

The mandibular condylar cartilages from normal and rachitic weanling rats were stained with ruthenium red to demonstrate the distribution of proteoglycan. In the rachitic animal there was an increased concentration of ruthenium-red positive granules in the pericellular region of chondrocytes from the extended hypertrophic zone when compared with the controls. These aggregates may represent unmodified proteoglycan which excludes calcium and thereby prevents matrix calcification.

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PubMed1988

The ultrastructure of dentine from rat incisors following exposure to sodium fluoride and potassium pyroantimonate staining.

Weanling rats were given a single intraperitoneal injection of sodium fluoride and control animals normal saline for four consecutive days. The fluoride produced a consistent response in the mineralizing dentine of the incisors in which a hypermineralized band was succeeded by a hypomineralized band. Potassium pyroantimonate staining for calcium ions showed that following injection of fluoride, in contrast to the controls, there were large amounts of calcium pyroantimonate in the pre-dentine and throughout the odontoblasts. This suggests that fluoride temporarily affects the membrane enzyme systems which maintain calcium concentration gradients between the odontoblasts and the matrix. The resultant influx of calcium is probably associated with the hypermineralization of the dentine matrix in which more hydroxyapatite crystallites are deposited. Upon recovery of the odontoblasts the matrix is relatively depleted of calcium resulting in matrix hypomineralization.

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PubMed1987

The effect of Candida albicans on the permeability of rat palatal epithelium: an ultrastructural and biochemical study.

The effect of a palatal acrylic appliance and/or infection with Candida albicans on the permeability of rat palatal epithelium has been investigated. Although normal rats, or rats inoculated with Candida albicans but without a prosthesis, had a barrier to perfused lanthanum, some low-molecular-weight proteins were able to pass through the epithelium. When infection was established by inoculation of Candida albicans under an acrylic plate, the epithelium became permeable to perfused lanthanum. Polyacrylamide gel electrophoresis of perfusates showed that a selective permeability to proteins was retained in such animals. Removal of acrylic plates from infected animals resulted in healing and restoration of the barrier to lanthanum.

Animals↗
PubMed1987

X-ray microanalysis of growth cartilage after rapid freezing, low temperature freeze drying and embedding in resin.

This paper reviews the work undertaken on the X-ray microanalysis of growth cartilage particularly in relation to matrix calcification. Attention is focused on the methodology available to accurately localize and retain the elements of interest. A method is described which involves rapid freezing, low temperature freeze drying in a custom built device, and embedding in Spurr resin. The results show that little tissue damage occurs and that elements of physiological interest are accurately localized at the sub-cellular level. Where damage occurs to chondrocytes as a result of freezing, however, dense intra mitochondrial granules are seen suggesting a phase transformation takes place resulting in the precipitation of calcium phosphate. Further improvements may be made in retaining the more labile elements such as K by using resins which polymerize at low temperature.

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PubMed1987

Scanning electron microscopy of the wall of the ovine cervix uteri in relation to tensile strength at parturition.

There was a progressive loosening of the collagenous fibre bundles in the stroma of the ovine cervix during spontaneous parturition. The change from an organ with predominantly thick collagen fibre bundles to one with a loose network of collagen fibrils was associated in time with a threefold increase in softness as measured by the Stretch modulus. Infusion of oestradiol 17 beta (E2 beta) for 18 hours elicited similar changes in the structure and mechanical properties of the cervix. Infusion of sodium meclofenamate for 18 hours significantly (P less than 0.005) reduced the effect of E2 beta administered simultaneously.

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PubMed1985

An inexpensive device for freeze drying and plastic embedding tissues at low temperatures.

The preparation of biological tissues for electron microscopy by rapid freezing retains the original localization of ions and molecules. A reproducible freezing regime was established by quenching tissues in liquid propane according to the method of Elder et al. (1981). Tissue was thereafter freeze dried in a custom built freeze drying device with a liquid nitrogen cooled stage to prevent ice recrystallization during drying. The device was also designed to allow the vacuum embedding of tissue in low temperature resin such as Lowicryl and polymerization in situ. This paper describes the design of the device and an example of its use in the freeze drying of cartilage. The results show that minimal ice damage occurs to the chondrocytes and that intracellular organelles are clearly visible. The regime described may prove a useful and pragmatic alternative to cutting tissue in the frozen state. Translocation of elements is unlikely except perhaps in the case of very labile elements such as Na and K, but this remains to be fully elucidated.

Animals↗
PubMed1985

Ultrastructure and energy-dispersive x-ray microanalysis of cartilage after rapid freezing, low temperature freeze drying, and embedding in Spurr's resin.

In order to undertake meaningful high-resolution x-ray microanalysis of tissues, methods should be used that minimize the introduction of artefacts produced by loss or translocation of ions. The most ideal method is rapid freezing but the subsequent sectioning of frozen tissues is technically difficult. An alternative method is to freeze dry the tissues at a low temperature, and then embed them in resin. This facilitates the rapid production of reproducible thin sections. With freeze-dried, embedded hypertrophic cartilage, the morphology was similar to that seen using aqueous fixatives even when no additional electron density is introduced by the use of osmium vapor. Energy-dispersive analysis of specific areas show that little or no loss or migration of ions occurs from structures such as mitochondria. Mitochondrial granules consisting of calcium and phosphorus precipitates were not observed except where the cells were damaged as a result of the freezing process. This may suggest that these granules only appear when tissue is damaged because of inadequate preservation.

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PubMed1984

The ultrastructure of the rat incisor odontoblast in organ culture.

Extracted incisors were dissected free of adherent soft tissue, split by a longitudinal incision lingually and the pulp sac carefully removed. The predentine-dentine pieces with attached odontoblasts were incubated for up to 24 h in culture medium in 5 per cent CO2, humid air at 37 degrees C. The cultures were recovered and processed for light microscopy and transmission electron microscopy. Examination of the explants showed a homogeneous layer of odontoblasts attached to the dentinal surface. The odontoblasts had a normal structure and nuclear polarity similar to that seen in vivo. There were no apparent degenerative changes.

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PubMed1984

The effects of lanthanum on the ultrastructure of hypertrophic chondrocytes and the localization of lanthanum precipitates in condylar cartilages of rats fed on normal and rachitogenic diets.

Ionic lanthanum was used to examine the distribution of calcium-binding sites in the condylar cartilages of rats that had been fed on normal and/or vitamin D-deficient rachitogenic diets for 4 weeks. Certain specific changes in the ultrastructure of the cartilage were attributed to the presence of the trivalent cation in the fixation medium. Cartilages from the rachitic animals showed a marked reduction in the quantity of lanthanum deposition on the outer surface of the chondrocytes and in the extracellular matrix. Returning rachitic rats to the control diet resulted in a corresponding return to a normal ultrastructural distribution of lanthanum in the condylar cartilages. No intracellular lanthanum deposits were observed. The results suggest that a vitamin D-dependent calcium-binding component may be an integral part of the chondrocyte plasma membrane structure.

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PubMed1982

Computer analysis of the surface ultrastructural features of porcine oral mucosa.

The surface features of histologically definable regions were recorded from standardized random scanning-electron micrographs. Computer-based discriminant and cluster statistical analyses were used to determine whether these surface features reflect only degrees of keratinization or are specific characteristics of each mucosal site. It was possible to distinguish consistently between keratinized and non-keratinized mucosa but, as a means of individual tissue identification, the analysis offered no advantages over conventional histological examination.

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PubMed1980

Ultrastructural localization of calcium in the mandibular condylar growth cartilage of the rat.

The potassium pyroantimonate technique was utilized for the selective subcellular localization of calcium in the mandibular condylar cartilage of 1-day-old rats. Electron dense calcium pyroantimonate precipitates were localized principally in mitochondria and at the cell membrane of the chondrocytes. In addition, small intracellular vesicles 0.1-0.2 micrometers in diameter were observed in proximity to the cell membrane of chondrocytes of the mid-hypertrophic zone. The results suggest that these vesicles were being extruded from the cell into the extracellular matrix. Energy-dispersive analysis by X-rays confirmed that calcium is the principal cation of the electron-dense precipitates.

Animals↗
PubMed1979

The use of the potassium pyroantimonate-osmium method as a means of identifying and localizing calcium at the ultrastructural level in the cells of calcifying systems.

Potassium pyroantimonate-osmium has been used to localize calcium as an electron dense precipitate in the odontoblast, ameloblast and early hypertrophic chondrocytes of the mandibular condylar growth cartilage. The precipitate exhibited a specific association with various cell organelles. The presence of calcium in the precipitates was confirmed using energy dispersive analysis by x-rays. It is suggested that this K-pyroantimonate method provides an accurate technique for the investigation of the subcellular localization of calcium in calcifying systems.

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