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  • 1
    Electronic Resource
    Electronic Resource
    Calcium distribution in freeze-dried enamel organ tissue during normal and altered enamel mineralization (1984)
    Springer
    Calcified tissue international 36 (1984), S. 596-603 
    Details
    ISSN: 1432-0827
    Keywords: Calcium ; Ameloblasts ; X-ray microanalysis ; Transport ; Frozen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Energy dispersive X-ray microanalysis was applied to freeze-dried blocks of enamel organ tissue to determine levels of calcium in various celular regions. The tissue blocks were dissected free from adjacent forming enamel following injection of cobalt or fluoride ions, both of which temporarily inhibit enamel mineralization. In all control and experimental specimens there was an increasing gradient of calcium from the stratum intermedium cells to the distal ends of the ameloblasts. Calcium levels were significantly reduced near the distal ends of the ameloblasts following cobalt or fluoride injection as compared with controls. It is suggested that evidence of an intercellular buildup of calcium near the distal ends of the ameloblast supports a controlling function of these cells. The changes in calcium levels are correlated with alterations in mineralization known to occur in the adjacent enamel of the model systems employed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02405373
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  • 2
    Electronic Resource
    Electronic Resource
    Potential toxins of acute liver failure and their effects on blood-brain barrier permeability (1983)
    Springer
    Cellular and molecular life sciences 39 (1983), S. 988-991 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effects of potential toxins of hepatic coma on the blood-brain barrier (BBB) permeability of the rat have been examined using the Oldendorf technique. Classical toxins of hepatic failure such as ammonia, methyl octanoate, mercaptans, and phenol caused significant increases in BBB permeability. A slight increase in permeability occurred following infusion of peroxidized linoleic acid and unconjugated bilirubin but no increase after infusion of bile acids.E. coli endotoxin infused into rats following partial hepatectomy also increased the BBB permeability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01989765
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of colchicine on lysosomal structures in maturation-ameloblasts of the rat incisor (1990)
    Springer
    Cell & tissue research 260 (1990), S. 565-573 
    Details
    ISSN: 1432-0878
    Keywords: Enamel ; Ameloblasts ; Colchicine ; Lysosomes ; Resorption ; Rat (Sprague-Dawley)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The lysosomal systems in maturation-ameloblasts affected by colchicine were examined using trimetaphosphatase cytochemistry. Demineralized segments of rat incisor were incubated for trimetaphosphatase. At all time intervals, lysosomal structures exhibited reduced enzyme reactivity and were clustered in the Golgi region of the cell. Both ruffle-ended and smooth-ended ameloblasts maintained essentially normal morphology up to 4 h after colchicine injection, except for some migration of organelles. After 8 h, the ruffled border was markedly modified and the associated dense granular material was no longer present. Changes in the lysosomal system and ruffled border indicate interference by colchicine with a putative resorptive function of the maturation-ameloblasts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00297237
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  • 4
    Electronic Resource
    Electronic Resource
    Fine structure of the secretory and non-secretory ameloblasts in the frog. II. Fine structure of the non-secretory ameloblastThis investigation was supported in part by USPHS Research Grant DE 3724. (1978)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 158 (1978), S. 181-197 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The non-secretory ameloblasts present at the enamel-free surfaces of maxillary teeth in the frog Rana pipiens were examined by electron microscopy at different stages of tooth development. Their main fine structural features seem to reflect a transport function. During early tooth development, the non-secretory ameloblasts adjacent to odontoblasts and predentin exhibit extensive lateral surface specializations and numerous cytoplasmic vesicles. During late tooth development, the non-secretory ameloblasts adjacent to mineralizing dentin show numerous cellular junctions, well-developed intercellular channels with numerous interdigitating processes and labyrinthine configurations at their distal surfaces. An intact basal lamina is present between the non-secretory ameloblasts and the dentin surface until the dentin becomes fully mineralized. At this stage the adjacent cells no longer exhibit surface specializations.It is suggested that the non-secretory ameloblasts may participate in the mineralization of adjacent dentin at the enamel-free surfaces. This surface dentin becomes fully mineralized at a later stage of development than the underlying dentin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1051580205
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  • 5
    Electronic Resource
    Electronic Resource
    Fine structure of the epithelial dental organ in the frog during early odontogenesisThis investigation was supported in part by USPHS research grant DE 02201-03 and USPHS-GRSG-FR 5309. (1970)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 168 (1970), S. 79-91 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A total of 227 tooth germs in different developmental stages were dissected from the maxillae of 58 leopard frogs (Rana pipiens). Five fixatives and three buffers were used and optimum preservation of the odontogenic epithelium was observed in specimens fixed in cold 4% glutaraldehyde at pH 7.3 for three hours followed by 1% osmium tetroxide for one hour. The inner dental epithelium showed mitotic figures limited to the initial stage of odontogenesis. The cells contained numerous free ribosomes, tonofilaments, few mitochondria and sporadic cisternae of endoplasmic reticulum. Their distal portions were drawn into processes studded with numerous hemidesmosomes. At a later stage of development yet prior to amelogenesis, these processes disappeared. The preameloblasts followed two pathways of histodifferentiation depending on their location. Ventrolabially the columnar cells exhibited progressive differentiation in contrast to the cuboidal cells on the ventrolingual surfaces of the cusps.The external dental epithelial cells were flattened, closely packed and connected by numerous desmosomes. Their cytoplasm contained mainly mitochondria and tonofilaments, as well as few Golgi vesicles. With the beginning of amelogenesis large intercellular spaces and lysosomal-like bodies were frequently observed and the Golgi complex is more prominent.We concluded that at early odontogenesis the epithelio-mesodermal interaction in the frog's dental organ is similar to that of mammalian species but the frog's internal epithelium shows a different pattern of histodifferentiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1091680107
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  • 6
    Electronic Resource
    Electronic Resource
    Fine structural changes and lysosomal phosphatase cytochemistry of ameloblasts associated with the transitional stage of enamel formation in the rat incisor (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 190 (1991), S. 279-290 
    Details
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Trimetaphosphatase (TMPase) and cytidine-5′-monophosphatase (CMPase) were used as lysosomal markers in the transitional ameloblasts (TA) to investigate the distribution of lysosomal structures and to correlate the cytochemical findings with the ultrastructural features of these cells. Of particular interest were the cytochemical and morphological changes which occur as the ameloblasts approach the maturation stage of enamel formation. The sequence of changes observed provides a basis for designation of three regions of the transitional zone (early and late TA and modulating ameloblasts). In the early TA region, the cells decreased in height and contained phagic vacuoles as well as numerous TMPase and CMPase reactive structures. Late transitional ameloblasts had invaginations at their distal ends as well as membrane-bound structures, both filled with fine granular material. Dense bodies, phagic vacuoles, and other elements of the lysosomal system were enzyme reactive. Modulating ameloblasts lacked the phagic vacuoles but exhibited large numbers of multivesicular bodies, vesicles, and secretory granules. Their distal ends were morphologically altered indicating a change towards ruffle- or smooth-ended varieties of maturation ameloblast. In the former, increased granular material was observed within cell membrane invaginations and associated membrane-bound structures. In the latter, intercellular spaces widened and were filled with granular material. The present cytochemical findings of an extensive lysosomal system in transitional ameloblasts confirm the function of those cells in reducing the secretory ameloblast population and in the selective elimination of their protein-synthesizing organelles. Furthermore, this extensive lysosomal system and the present morphological findings are consistent with a potential role for transitional ameloblasts in contributing to the marked loss of enamel protein known to occur during maturation.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001900308
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  • 7
    Electronic Resource
    Electronic Resource
    Fine structure of the secretory and nonsecretory ameloblasts in the frog. I. Fine structure of the secretory ameloblastsThis investigation was supported in part by USPHS Research Grant DE3724. (1977)
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 148 (1977), S. 161-193 
    Details
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Amelogenesis in the tooth germs of the frog Rana pipiens was examined by electron microscopy at different stages of tooth development. Cellular changes in secretory ameloblasts during this process showed many basic similarities to those in mammalian amelogenesis.Amelogenesis can be divided into three stages based on histological criteria such as thickness of enamel and the relative position of the tooth germ within the continuous succession of teeth. These stages are early, transitional and late. The fine structure of the enamel-secreting cells reflects the functional role of these ameloblasts as primarily secretory in the early stage, possibly transporting in the late stage and reorganizing between the two functions in the transitional stage. In early amelogenesis the cell exhibits well-developed granular endoplasmic reticulum, Golgi complex, microtubules, dense granules, smooth and coated vesicles, lysosome-like bodies in supranuclear and distal portions of the cell and mitochondria initially concentrated in the basal part of the cell. Numerous autophagic vacuoles are observed concomitant with the loss of some cell organelles at the transitional stage. During late amelogenesis the ameloblasts exhibit numerous vesicles, granules, convoluted cell membranes, junctional complexes and widely distributed mitochondria. Toward the end of amelogenesis, cells become oriented parallel to the enamel surface and the number of organelles is reduced.Amelogenesis in the frog is an extracellular process and mineralization seems to occur simultaneously with matrix formation.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001480202
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