Biomedical subjects

A L Arsenault

Publications and source records attributed to A L Arsenault.

At least 37 records · Page 2Linked to original sources

PubMed1990

Vascular invasion of the epiphyseal growth plate: analysis of metaphyseal capillary ultrastructure and growth dynamics.

Metaphyseal blood vessels which invade the calcifying epiphyseal growth plate were examined by a variety of techniques to determine their morphology, cell division, and growth patterns as they relate to endochondral ossification. Four regions of these vessels were characterized: 1) sprout tips--the terminal ends of the capillary sprouts which impinge upon the hypertrophic chondrocytes of the growth plate; 2) region of extended calcified cartilage--those deeper vessels within the metaphysis which are surrounded by an extracellular matrix predominantly composed of extended septa of calcified cartilage; 3) region of bone deposition--further still from the epiphysis these microvessels are contained within a network of active bone deposition laid upon a scaffold of calcified cartilage; 4) region of primary vessels--at a distance of 350-500 microns from the epiphysis are dilated vessels with one or two layers of smooth muscle in their walls, which supply and drain the metaphyseal capillary plexus. The sprout tips are continuous blind-ended vessels lined with an attenuated endothelium with no underlying basement membrane. Dividing endothelial cells are most frequently found in the region of bone deposition 175-200 microns behind the apices of the growing sprout tips. A time-coursed, autoradiographic examination of cytokinesis revealed radio-labelled endothelial cells to appear at the epiphysis after a 24 hr period. The metaphyseal capillary sprouts represent a continuous, unidirectional angiogenic vascular network which grows by elongation from the region of bone deposition; this region remains a fixed distance behind the sprout tips. These findings are discussed in light of the growth dynamics between this vascular plexus and the epiphyseal growth plate.

Animals↗

PubMed1990

Endothelial cell division in metaphyseal capillaries during endochondral bone formation in rats.

Endothelial cell division in the metaphyseal capillaries of growing rats was studied by serial sectioning and electron microscopic examination. The endothelium of these capillary sprouts forms a continuous attenuated squamous lining. During endochondral bone formation these growing vessels possess a region of endothelial cell division which is located behind the sprout tip in an area where the microvascular wall consists of an endothelium and a discontinuous layer of perivascular cells. Examination of this region has shown the presence of junctional attachments between daughter cells even before cell separation is complete. Thus, the integrity of the vascular wall is not compromised during cell division. Junctional complexes with adjacent endothelial cells are also formed along the cleavage plane prior to the completion of cytokinesis. Numerous microvilli and from both the daughter cells and adjacent endothelial cells often make contact and form junctions with the plasma membrane of the dividing cells. A model for endothelial junction formation between daughter cells during cytokinesis and the role that microvilli play in the process is proposed.

Animals↗

PubMed1990

Vascular canals in bovine cortical bone studied by corrosion casting.

The architecture of vascular canals in cortical bovine bone was studied by a corrosion casting method. Prior to perfusion of the casting polymer, both cellular and nonmineralized components were removed to ensure proper impregnation into vascular canals--haversian and Volkmann's canals within secondary osteons and the vascular canals of periosteal circumferential lamellae. The resulting castings revealed an anastomotic system of canals within and between these two regions of cortical bone. The nature of these arborizations, their varying degrees of interconnectiveness, and their spatial, three-dimensional ordering are clearly demonstrated in this study.

Animals↗

PubMed1989

Image analysis of electron micrographs relating to mineralization in calcifying cartilage: theoretical considerations.

Biological mineralization kis a cell-mediated process which is believed to be triggered by a "nucleating agent." Various matrix structures, such as matrix vesicles, collagen fibrils and macromolecules, have been claimed to be the source of this substance, since these components have been found by transmission electron microscopy (TEM) of thin sections to be associated with early mineral crystals. Systematic image analysis of the relationships revealed in electron micrographs between specific matrix components and early mineral deposits has shown that unequivocal image interpretation is not possible. This is due principally to the problems posed by overprojection and truncation phenomena, since the structures being analyzed lie within the same dimensional range as thin section thickness. Various examples are illustrated and discussed. The site at which mineral crystals are initially laid down thus cannot be identified with any matrix structure using thin section TEM. Possible technical approaches to resolve this problem of image analysis are discussed.

Animals↗

PubMed1989

The dentino-enamel junction: a structural and microanalytical study of early mineralization.

The spatial localization of enamel and dentin apatite crystals of the rat tooth has been studied by electron microscopic methods--bright field, selected-area dark field, and electron spectroscopic imaging. The sequential events of dentin calcification followed by the formation and growth of enamel crystals were determined and compared to previous studies. In dentin, initial sites of mineral deposition occur in areas subjacent to the dentino-enamel junction (DEJ). The subsequent expansion of these deposits progresses towards the DEJ to the terminal ends of dentin collagen fibrils. Concomitantly, an electron-dense enamel matrix is released by ameloblasts; with the presence of this matrix, the growth of enamel crystals occurs from the underlying calcified dentin. Enamel crystal growth continues to within close proximity of the plasma membrane of ameloblasts. A close spatial relationship between enamel and the crystals of calcified dentin collagen fibrils was observed by selected-area dark field imaging. Such areas of crystal intimacy show a co-localization of calcium and phosphorus extending from calcified collagen fibrils to enamel sheaths which encase enamel crystals. A working model of the spatial relationship between crystals of dentin and enamel is presented and discussed in light of mechanisms by which calcified dentin may promote the formation of enamel crystals.

Amelogenesis↗

PubMed1989

A comparative electron microscopic study of apatite crystals in collagen fibrils of rat bone, dentin and calcified turkey leg tendons.

Crystal-collagen relationships in calcified turkey leg tendons and cortical bone and dentin of the rat were studied by bright field and selected-area dark field electron microscopy. The latter imaging technique enables the specific and direct visualization of apatite crystal sizes and their crystallographic orientations within collagen fibrils. Cortical bone possessed the longest mean c-axial length (170 +/- 50 A), then the tendon (142 +/- 43 A) and the smallest was dentin (110 +/- 30 A). Crystallographic orientations of apatite were found to alternate between a,b- and c-axial planes along the axial period of longitudinally sectioned collagen. This distribution of apatite may reflect a crystal alignment with collagen molecules as they spiral in superhelical fashion along the long axis of the collagen fibril. Apatite crystals were localized within both the gap and overlap zones of collagen fibrils even at very early stages of mineralization. The relative amounts of mineral within single collagen periods were determined as a function of electron absorbency. In the tendon at the onset of mineralization 80% of the mineral was located in the gap zone and 20% in the overlap zone; with further mineralization these relative amounts changed to 55% in the gap zone and 45% in the overlap zone. This 55/45% ratio observed in the heavily mineralized tendon was also observed in both cortical bone and dentin. The implications of these findings are discussed in view of collagen molecular ordering and the spread of apatite along collagen fibrils.

Animals↗

PubMed1989

Freeze-substitution staining of rat growth plate cartilage with alcian blue for electron microscopic study of proteoglycans.

To selectively stain polyanionic macromolecules of growth plate cartilage and to prevent artifacts induced by aqueous fixation, proximal tibial growth plates were excised from rats, slam-frozen, and freeze-substituted in 100% methanol containing the cationic dye Alcian blue. Electron microscopic examination showed the tissue stained with Alcian blue to be comparable in ultrastructural preservation to tissues slam-frozen and freeze-substituted in the absence of Alcian blue. The extracellular matrix exhibited a characteristic staining pattern when stained by this method. The pericellular rim was identified as a band of varying width encircling the chondrocyte and its cell processes. Peripheral to the pericellular rim the heterogeneity of staining within the extracellular matrix increased, taking the form of polymorphic densities. X-ray microanalysis showed that the visual interpretation of electron density was related to the concentration of copper present, and that the concentration of sulfur was variable in the pericellular rim and in the interterritorial matrix. The difficulties associated with aqueous fixation and staining procedures are discussed in contrast to the improved preservation achieved by cryogenic methods.

Alcian Blue↗

PubMed1989

Vesicle- and collagen-mediated calcification in the turkey leg tendon.

The distribution, organization, and orientation of apatitic mineral associated with vesicles and collagen in normal calcifying turkey leg tendon have been examined to determine inorganic-organic interactions in this vertebrate tissue. The study utilized selected area electron diffraction and bright or dark field transmission electron microscopy of thin sections (approximately 70 nm) treated by anhydrous means. Bright field microscopy revealed crystals randomly disposed in radial clusters related to vesicles or highly oriented related to collagen. Dark field images of the crystal c-axis were localized within some hole zone regions of collagen but were generally sparse in vesicles. Images of mineral a,b-axes were associated with vesicles and also appeared in collagen hole zones complementary to those containing c-axis images. Where mineralization of vesicles occurred adjacent to that of collagen, bright and dark field images provided suggestive evidence that the crystals could be contiguous at some sites, but the bulk of extracellular mineralization was spatially discontinuous. The varying disposition of mineral in vesicles and collagen is likely indicative of distinct mechanisms of nucleation in these components, the complementary orientation of mineral c- and a,b-axes in collagen may provide insight into the structure and organization of the protein, and the distribution of vesicle-mediated mineralization appears to contribute to apatite accumulation between collagen fibrils.

Animals↗

PubMed1989

Pigment resembling atmospheric dust in Peyer's patches.

Terminal ileal pigmentation was observed during colonoscopy, in surgically resected specimens, and autopsy cases. Microscopically, black pigment was seen within macrophages in the lamina propria and submucosa, closely related to the Peyer's patches. Three ilia from autopsies with no macroscopic pigmentation showed deposits following digestion and X-ray microanalysis. X-ray microanalysis of tissue sections and digestates revealed a heterogenous population of particles. Approximately one third of the particles contained calcium and phosphorus and were considered endogenous. The rest of the particles were predominantly aluminum and magnesium-rich silicates, which were considered exogenous. Analysis of particulate extracted from lungs and ilea of four autopsy cases demonstrated remarkable similarities in composition. These findings suggest that the ileal deposits are derived from atmospheric dust. This pigment is believed to migrate into the Peyer's patches through the M cells of the follicle associated epithelium, although other mechanisms for pigment deposition cannot be ruled out.

Dust↗

PubMed1988

Altered plasma membrane ultrastructure in multidrug-resistant cells.

Multidrug resistance is mediated by P-glycoprotein, an integral plasma membrane component which is thought to function as a drug export pump. This model can explain drug resistance, but fails to account for the broader pleiotropy of the multidrug resistance phenotype. We report here a freeze-fracture study revealing increases in the densities of protoplasmic face intramembrane particles in multidrug-resistant Chinese hamster ovary (CHO) and human leukemic cells. The intramembrane particle density in a CHO cell revertant which had lost the characteristics of the multidrug resistance phenotype was indistinguishable from that of the drug-sensitive parental cell line. This demonstration of a global multidrug resistance-linked change in plasma membrane architecture may have significant implications for understanding the variety of concurrent membrane-related changes which are not easily explained by the current model for multidrug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1988

Aluminum intoxication in vitamin D-deficient rats: studies of bone aluminum localization and histomorphometry before and after vitamin D repletion.

Aluminum accumulation by both dialysis patients and nonuremic patients, requiring chronic total parenteral nutrition, may be an etiological factor in the development of severe osteomalacia. To study the role of aluminum toxicity in bone, further experiments have been conducted in the nonuremic, vitamin D-deficient rat. Weanling rats were raised on vitamin D-deficient diets, and half received parenteral aluminum (5 mg/wk), for 30 days. In the first experiment low doses of 25-OH cholecalciferol (500 ng/week) were given subcutaneously for a further 30 days. Control rats were maintained on a similar protocol, but were supplemented with cholecalciferol (5 micrograms/week) from the outset until sacrifice at 60 days. In the second experiment a single bolus of cholecalciferol (5 micrograms) was given to study short-term changes in serum biochemistry and bone histology at 96 hr. Quantitative bone histomorphometric analyses of the proximal tibial metaphysis were made in all experimental groups. In the experimental vitamin D-deficient group, with the highest bone aluminum content (as assessed by extraction of whole bone aluminum), X-ray microanalysis was performed to determine the distribution of aluminum in bone tissue and bone cell organelles. The results showed that control rats treated with prolonged aluminum therapy (30 mg over 60 days) had evidence of both reduced osteoid matrix synthesis and mineralization. However, in vitamin D-deficient rats, there was no evidence that aluminum exacerbated the osteomalacic lesion, even though there was histochemical evidence of aluminum deposition at the bone-osteoid interface.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum↗

PubMed1988

Crystal-collagen relationships in calcified turkey leg tendons visualized by selected-area dark field electron microscopy.

The distribution and orientation of biological apatite crystals in calcified turkey leg tendons were studied by selected-area dark field electron microscopy. This imaging technique enables the direct visualization of apatite and the specific determination of the crystallographic axes (a, b-axes or c-axis) within calcified collagen fibrils. This study shows that at early stages of mineralization, rod-shaped apatite crystals (5-20 nm in length) were localized and dispersed within gap zones bordering both the collagen molecule C- and N-terminal regions. At later stages of mineral deposition the crystals were more extensive, occupying greater areas of the gap zone and, in addition, apatite crystals were found to occur in the overlap zones. The orientation of apatite crystals was observed to be an alternating and interlocking distribution of a, b-axes and c-axis along the axial period of collagen fibrils. This distribution is interpreted as representing a continuous rotation of apatite axial orientation along the collagen period.

Animals↗

PubMed1988

Crystals in calcified epiphyseal cartilage and cortical bone of the rat.

The size of hydroxyapatite (HAP) crystals in calcified cartilage and cortical bone of the rat has been studied and compared with that of synthetic poorly crystalline hydroxyapatite (PCHA). Crystal size was determined by X-ray diffraction and selected-area dark field imaging, and their elemental compositions were determined by emission spectroscopy. The crystal size of cartilage, bone, and PCHA were found to be between 120 and 170 A in length by 50 A in width as determined by both X-ray diffraction and dark field imaging. Cartilage had a lower ash weight than bone but both have the same Ca/P ratio of 1.6. These findings, though in agreement with the X-ray diffraction literature, differ from observations made by conventional bright field electron microscopy. We conclude that mineral sites in cartilage and bone, which exist as platelike structures, are in fact aggregates of small 120-170 X 50 A HAP crystals. The consequences of these findings was discussed in view of crystal relationships with collagen and other macromolecules.

Animals↗

PubMed1988

Electron microscopic analysis of mineral deposits in the calcifying epiphyseal growth plate.

Early mineral deposits within calcifying rat epiphyseal growth plates were studied by bright field and selected-area dark field electron microscopy, and X-ray microanalysis. These mineral deposits were prepared in situ by high-pressure freezing, freeze substitution, and low-temperature embedding, and were examined in unstained, stained, and ethyleneglycol tetraacetic acid (EGTA)-treated stained thin sections. On unstained sections mineral rods occur within an amorphous density of calcium and phosphorus (CaP). X-ray microanalysis of stained sections reveals that the location of electron-dense deposits does not always correspond to that of the CaP mineral deposits identified in electron microscopic images. Such an analysis showed a depletion of both Ca and P in stained sections at sites corresponding to high levels of these elements in unstained sections. Staining thus demineralizes early deposition sites of CaP; at the same time lead (Pb) and uranium (U) bind to the organic components of the extracellular matrix formerly associated with Ca and P. This substitution phenomenon alters the overall fine structure of mineral sites by depleting the amorphous density of Ca and P, and by creating isolated rodlike structures that have formerly been interpreted as representing hydroxyapatite (HAP) crystals. Selected-area dark field imaging shows nascent sites of HAP crystals to be associated with the limiting membrane of matrix vesicles, but such crystals were undetectable at these sites with conventional bright field images. Dark field imaging also showed that the typical 30-80 nm crystal rods found in calcified cartilage consist of aggregates of HAP crystals.

Animals↗

PubMed1988

An electron microscopic and spectroscopic study of murine epiphyseal cartilage: analysis of fine structure and matrix vesicles preserved by slam freezing and freeze substitution.

Newborn mice epiphyseal growth plates were preserved by slam freezing/freeze substitution and examined by conventional electron microscopy, stereopsis, high voltage electron microscopy, and electron spectroscopic imaging (ESI). To illustrate the improved ultrastructure of this cryogenic procedure, conventional, aqueously fixed growth plates were included showing collapsed hypertrophic chondrocytes surrounded by a depleted and condensed extracellular matrix. In contrast, the cryogenically prepared epiphyses contain chondrocytes and extracellular matrix vesicles both in direct contact with proteoglycan filaments retained in an expanded state. ESI is an electron microscopic technique which enables the direct localization of atomic elements superimposed over fine structural details. This technique was used to examine the colocalization of calcium and phosphorus within matrix vesicles and within their associated extracellular environments. Matrix vesicles appeared in three distinct diameter ranges. The integrity of the matrix vesicles was examined at various stages of mineralization and also within the mineralized zone of provisional calcification.

Animals↗

PubMed1987

Microvascular organization at the epiphyseal-metaphyseal junction of growing rats.

The microarchitecture of the rat metaphyseal nutrient artery, the major blood supply to the calcifying epiphyseal growth plate, was studied by light microscopic serial sections, model reconstruction of serial sections, and scanning electron microscopy of plastic corrosion castings. These techniques illustrate how the metaphyseal artery undergoes extensive arborization and anastomosis upon route through the metaphysis. From this vascular network, closed capillary sprouts abut hypertrophic chondrocytes bordered by scaffolds of mineralized matrix.

Animals↗

PubMed1987

Improved preservation of cartilage extracellular matrix by freeze dried embedding.

A freeze dried embedding procedure is described and used to study the extracellular cartilage matrix of the epiphyseal growth plate. This method provides improved fine structural preservation of the extracellular matrix over conventional fixation and appears comparable to that attained by freeze substitution. The trabecular networks of expanded proteoglycan filaments are illustrated in stereo-images.

Animals↗

PubMed1984

The dynamics of exoskeletal-epidermal structure during molt in juvenile lobster by electron microscopy and electron spectroscopic imaging.

The exoskeletal-epidermal complex of juvenile lobsters at various stages throughout the molt cycle was examined by conventional electron microscopy, freeze-etch replicas, and electron spectroscopic imaging. This latter technique which enables the direct localization of atomic elements superimposed over morphological fine structure has been applied to this tissue complex to determine the spatial distributions and interrelationships of calcium, phosphorus, and sulphur. Chitin microfibril assembly is visualized in thin sections as occurring at the surface of apical membrane plaques which in freeze-etch replicas invariably possess a rich distribution of intramembrane particles on both P and E faces. In early stages of mineralization the exo- and endocuticular zones of the exoskeleton possess a dense Ca-containing lamellar repeat. These bands are unrelated to the helicoidal arrangement of chitin microfibrils. At later stages of development mineral deposits occur within the exocuticle and advance through to the endocuticle. These deposits align with chitin microfibrils and exhibit a helicoidal pattern. Morphological and chemical alterations associated with mineralization and demineralization of the exoskeleton are discussed.

Animals↗