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  • 1
    Electronic Resource
    Electronic Resource
    Localization of epidermal growth factor receptors in cells of the enamel organ of the rat incisor
    Amsterdam : Elsevier
    Developmental Biology 148 (1991), S. 590-601 
    Details
    ISSN: 0012-1606
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0012-1606(91)90276-9
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  • 2
    Electronic Resource
    Electronic Resource
    Immunolocalization of the Cation-Independent Mannose 6-Phosphate Receptor and Cathepsin B in the Enamel Organ and Alveolar Bone of the Rat Incisor (1996)
    Springer
    Calcified tissue international 59 (1996), S. 192-199 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Mannose 6-phosphate receptor — Cathepsin B — Ameloblast — Immunocytochemistry.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. In order to examine our hypothesis that maturation ameloblasts could degrade the enamel matrix in a manner analogous to bone resorption mediated by osteoclasts, we have assessed the distribution of lysosomal enzymes in the enamel organ by immunolocalizing the cation-inindependent mannose 6-phosphate receptor (MPR) and the lysosomal enzyme cathepsin B at all stages of amelogenesis. Secretory ameloblasts showed strong immunoreactivity for MPR in the supranuclear Golgi region and in the cytoplasm between the Golgi region and the distal junctional complexes. However, cathepsin B immunoreactivity was mainly seen in the distal portion of Tomes' process, which was unreactive for MPR immunogenicity. In maturation ameloblasts, the MPR was observed on the ruffled border of the ruffle-ended ameloblast (RA) but not on the distal cell membrane of the smooth-ended ameloblast (SA), although both cell types demonstrated strong immunoreactivity for MPR in the Golgi region. Immunoreactive cathepsin B was seen at the distal ends of both RA and SA. It is postulated that the nascent lysosomal enzymes bind to the mannose 6-phosphate receptors which target them not only to intracellular lysosomes, but also to the ruffled border of maturation ameloblasts where these enzymes are secreted into the enamel. Since MPR and lysosomal enzymes were also detected on the ruffled border of osteoclasts (Ocl) adjacent to alveolar bone, our immunocytochemical approach provides strong evidence for a similarity between the maturation process in enamel, as mediated by the ruffle-ended maturation ameloblasts, and bone resorption mediated by osteoclasts. This study has established that a common mechanism, based on MPR-targeted lysosomal secretion and matrix degradation, is basic to the maturation process involved in calcified tissues as different as bone and enamel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002239900108
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  • 3
    Electronic Resource
    Electronic Resource
    Modification of the enamel maturation pattern by vinblastine as revealed by glyoxal bis(2-hydroxyanil) staining and 45calcium radioautography (1986)
    Springer
    Histochemistry and cell biology 86 (1986), S. 141-145 
    Details
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Patterns characteristic of enamel maturation can be visualized at the surface of the rat incisor by staining with glyoxal bis(2-hydroxyanil) (GBHA) and radioautography following 45calcium injection. In this study, the effects of vinblastine on enamel maturation were monitored by these two methods. At 4 h after injection of vinblastine, the darkly-stained GBHA bands had widened incisally into the interband regions when compared to normal, control teeth. Radioautography at 5 min after calcium injection in vinblastine-treated animals (4 h) showed a modified maturation pattern of weaker labeling and less distinct banding. At 8 h after vinblastine injection, most of the enamel stained uniformly with GBHA, and bands and interband regions could not be resolved. Radioautography at 5 min after calcium injection showed that the 8 h vinblastine treatment removed the banding pattern, leaving only a weakly-labeled area. Vinblastine is known to destroy and prevent the formation and turnover of microtubules, and hence the formation of ruffled borders of ruffle-ended ameloblasts (Akita et al. 1983). The concomitant decrease in calcium incorporation implies that events taking place in relation to the ruffled border may affect calcium exchange or accretion within the enamel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00493379
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  • 4
    Electronic Resource
    Electronic Resource
    The fine structure of secretory ameloblasts in rat incisors (1968)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 161 (1968), S. 211-229 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The fine structure of the ameloblasts which secrete the inner enamel matrix in rat incisors was described using light and electron microscopy. The tissue was fixed by perfusion with 2.5% glutaraldehyde and gently decalcified in isotonic EDTA.The ameloblasts are tall cells forming a simple columnar epithelium. The base is adjacent to the stratum intermedium and the apex (Tomes' process) extends into newly-formed enamel. The infranuclear zone is divided by the basal cell web into a small basal bulge adjacent to the stratum intermedium, and a larger compartment containing most of the cell's mitochondria. The supranuclear zone contains the rough endoplasmic reticulum and the Golgi apparatus. The rough endoplasmic reticulum predominates in the proximal and distal regions of this zone where it occupies most of the cell width. In the intermediate region, the rough endoplasmic reticulum surrounds a central tubule-shaped Golgi apparatus, the tubule wall being made up of flattened saccules. The Golgi region of ameloblasts is associated with coated vesicles, two types of granules (light and dark) which may be lysosomes, and a characteristic dense content granule shown to be the enamel precursor (0.16 μ diameter).The supranuclear zone is separated from Tomes' process by the apical cell web. Tomes' process is devoid of endoplasmic reticulum and Golgi material, but contains numerous dense content granules as well as microtubules and coated vesicles. The amorphous dense content granules are the precursors of the highly orientated fibrous enamel matrix. The proximity of the process to the fibrous enamel suggests that it is involved in orientation of these fibrils. Since bundles of fibrils constitute rods, the process would seem also to be involved in enamel rod orientation.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1091610207
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  • 5
    Electronic Resource
    Electronic Resource
    A light and electron microscopic study of the nearly mature enamel of rat incisors (1971)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 169 (1971), S. 559-583 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The structure of the organic matrix close to the mature enamel in 100 gm rat incisors was studied by light and electron microscopy using EDTA decalcified teeth.Under the light microscope, in 0.5 μ Epon sections, the enamel layer of cross sectioned upper incisors was about 60 μ thick. The inner enamel was about 40 μ thick and consisted of an initial enamel layer (4 μ) adjacent to the dentin in which no rod profiles were seen, and an inner layer proper which contained six to eight rows of oval-shaped rod profiles set in a homogeneous background. The profiles in any given row were inclined mesially or laterally and alternated in adjacent rows. The outer enamel was about 20 μ thick and consisted of an outer enamel proper and a 2-4 μ thick final enamel layer which smoothed out the enamel surface. The outer enamel proper contained smaller elliptical rod profiles in a more abundant background. These profiles were not arranged in rows and were oriented at right angles to the enamel surface. The final enamel layer contained no rod profiles and was lined on its outer surface by a PA-Schiff positive layer resembling a basement membrane.Under the electron microscope the matrix of rod profiles and interrod material could be distinguished. This consisted of aggregated tubular (and filamentous) subunits, 250 Å in diameter, with empty space between them. Within the rod profiles the subunits ran parallel to the rod's long axis, whereas in the interrod material the subunits were again parallel but but running at right angles to the subunits of the rods. In addition to forming the material between the rods, the interrod material also formed the initial and final enamel layers.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1091690307
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  • 6
    Electronic Resource
    Electronic Resource
    Cellular renewal in the enamel organ and the odontoblast layer of the rat incisor as followed by radioautography using 3H-thymidine (1975)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 183 (1975), S. 523-561 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Renewal of the cell populations of the incisor was studied in 100 gm male rats injected with a single dose of 3H-thymidine and sacrificed at various times from one hour to 32 days after injection. Radioautographs showed that a cohort of labeled cells within the enamel organ, odontoblast layer, and pulp was carried passively with the erupting incisor from the apical end toward the gingival margin where the life cycle of these cells was terminated. Labeled cells in the upper and lower incisor, although traversing different absolute lengths, were found in approximately the same functional stage of their life cycle at similar times after the injection. Thus, by one and one-half days labeled ameloblasts began inner enamel secretion. By 32 days labeled ameloblasts had traversed the entire maturation zone and were located at the gingival margin. Labeled odontoblasts followed closely the movement of labeled ameloblast. The mean rate of ameloblast migration was 567 μm/day on the upper incisor and 651 μm/day on the lower. For the odontoblasts this rate was 500 μm/day (upper) and 631 μm/day (lower). Finally, it was found that as the rat aged, the duration of the life cycle for epithelial and pulp cell populations of the incisor increased because of growth within the longitudinal axis of the tooth. It was concluded that the apical end of the incisor literally “grows backward” in the bony socket, and hence, the duration of the life cycle becomes greater simply because it takes cells longer to physically reach the gingival margin.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1091830405
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  • 7
    Electronic Resource
    Electronic Resource
    A comparison of the protein synthetic activity of presecretory and secretory ameloblasts in rat incisors (1977)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 188 (1977), S. 143-171 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Presecretory ameloblasts were compared morphologically and functionally to secretory ameloblasts in the rat incisor. Structurally, the cell types are similar except for the absence of a Tomes' process at the presecretory stage. The developmental changes at the apical end of the ameloblast were described and correlated sequentially with the onset of extracellular events. First, a layer a amorphous dense material appeared at the dentinal surface adjacent to the ameloblasts. Second, the initial layer of enamel began to develop. Third, inner enamel secretion began with the appearance of interrod enamel. This occurred concomitantly with the appearance of the interdigitating portions of Tomes' processes.Functionally, the protein synthetic activity of presecretory ameloblasts was compared to secretory ameloblasts. Light microscopic radioautography of 1-m̈m thick Epon sections was used to localize 3H-proline and 3H-tyrosine at various times after injection. At time intervals up to 20 minutes the two presursors were localized as a band of labeled protein in the supranuclear cytoplasm of both presecretory and secretory ameloblasts. At 30 minutes an additional band of radioactivity was localized within the apices of both types of ameloblasts. In presecretory cells the apical reaction band was over the proximal portion of Tomes' processes which border on the dentin. In the secretory cells, the apical reaction band was over both proximal and interdigitating portions of Tomes' processes and over the enamel. Grain counts over the secretory ameloblasts showed that the incorporation of tyrosine increased by 7.5% as opposed to a 63% increase with proline when compared to the values in presecretory cells. The different increases with the two precursors were in keeping with the different amounts of the two amino acids reported to be present in enamel protein.It was concluded that while the secretory ameloblasts synthesize and secrete enamel protein, both presecretory and secretory cell types produce another category of protein which is involved in the apical reaction band. It was proposed that this material is structural protein being contributed to the continuously lengthening Tomes' process which is speculated to occur during formation of enamel.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1091880203
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  • 8
    Electronic Resource
    Electronic Resource
    The behavior of substances labeled with 3H-proline and 3H-fucose in the cellular processes of odontoblasts and ameloblasts (1981)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 200 (1981), S. 1-10 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Odontoblasts are cells with single cytoplasmic processes that grow longer as more dentin is elaborated. Ameloblasts also have single processes and it has been postulated that they too grow longer as more enamel is made. Support for this hypothesis was obtained using rat incisors to investigate the behavior of substances labeled with 3H-proline and 3H-fucose. A comparison was made between odontoblasts, which have processes known to grow and remain within the dentin, and the ameloblasts whose Tomes' processes are hypothesized to grow and leave remnants in the completed enamel. With 3H-proline, the odontoblast bodies are labeled at the early time intervals. They synthesize and secrete a layer of intensely labeled predentin, which by 1 and 2 days is converted to mineralized dentin. Matrix deposited after the main pulse is weakly labeled. Odontoblast processes are never labeled in dentin formed prior to injection. With 3H-fucose, the cell bodies are labeled at the early intervals and the newly formed glycoproteins are deposited into the predentin. Almost immediately, these are progressively added to the dentin at the calcification front. With time a gradient of labeling extends from the unlabeled dentin toward the odontoblast bodies. Unlike the behavior of labeled proteins, by 1 and 2 days labeled glycoproteins appear along the entire length of the odontoblast processes. In the enamel, no Tomes' processes are present during maturation. With 3H-proline, reactions are adjacent to the cells and diffuse toward, but do not reach the dentino-enamel junction by 1 and 2 days. With 3H-fucose, reactions appear over the enamel near the cells. By 1 and 2 days no diffusive pattern is seen, but grains are concentrated near the dentino-enamel junction, in a region containing holes known to be the beginning of Tomes' processes. Since odontoblast glycoproteins migrate along odontoblast processes, it was postulated that cytoplasmic remnants were present in enamel along which ameloblast glycoproteins could also migrate to reach the holes at the dentino-enamel junction.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1092000102
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  • 9
    Electronic Resource
    Electronic Resource
    In vivo demonstration by radioautography of binding sites for insulin in liver, kidney, and calcified tissues of the rat (1986)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 214 (1986), S. 130-140 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: An in vivo binding assay using radioautography was employed to visualize insulin receptors in rat tissues. Two and one-half minutes after the intravenous injection of 125I-insulin, free hormone was separated from bound hormone by whole body perfusion with lactated Ringer's solution followed by perfusion with glutaraldehyde. The localization of bound hormone, fixed in situ by perfusion with glutaraldehyde, was determined. Nonspecific binding of labeled insulin was noted in the proximal convoluted tubules of the kidney cortex, prebone and adjacent bone, predentin and adjacent dentin, and enamel. Specific binding sites were observed at the periphery of hepatocytes, over osteoblasts, and in relation to the endothelial cells of fenestrated capillaries within the papillary layer of the maturation zone of the incisors.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1092140205
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  • 10
    Electronic Resource
    Electronic Resource
    Specific binding sites for transferrin on ameloblasts of the enamel maturation zone in the rat incisor (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 218 (1987), S. 123-127 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: During enamel maturation in rodents, an iron-containing pigment is deposited into the surface layer of the enamel. Maturation zone ameloblasts presumably are responsible for this deposition. The presence of large amounts of ferritin in the cytoplasm of these cells suggests that they receive iron, presumably from circulating transferrin. An in vivo radioautographic binding assay using iodinated transferrin was used to determine if indeed maturation ameloblasts possess transferrin receptors at their cell surfaces. Experimental rats received systemic injections of labeled transferrin while control rats received injections of labeled transferrin plus a large excess of unlabeled transferrin in order to complete with the labeled transferrin for available specific receptors. Light microscope radioautography showed that ruffle-ended ameloblasts (RAs) of the enamel maturation zone had a high density of specific receptors for transferrin relative to smooth-ended ameloblasts (SAs). Electron microscopy and energy-dispersive X-ray spectroscopy confirmed the presence of ferritin and iron, respectively, within these cells. It is postulated that the iron responsible for enamel pigmentation is transported by transferrin to maturation ameloblasts and is bound to specific transferrin receptors found mostly on RAs and that the modulation of these cells into SAs results in a loss of most of these receptors.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1092180205
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