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  • 1
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 59 (1992), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: An improved DNase I inhibition assay for the filamentous actin (F-actin) and monomeric actin (G-actin) in brain cells has been developed. Unlike other methods, the cell lysis conditions and postlysis treatments, established by us, inhibited the temporal inactivation of actin in the cell lysate and maintained a stable F-actin/G-actin ratio for at least 4-5 h after lysis. The new procedure allowed separate quantitation of the noncytoskeletal F-actin in the Triton-soluble fraction (12,000 g, 10 min supernatant) that did not readily sediment with the Triton-insoluble cytoskeletal F-actin (12,000 g, 10 min pellet). We have applied this modified assay system to study the effect of hypothyroidism on different forms of actin using primary cultures of neurons derived from cerebra of neonatal normal and hypothyroid rats. Our results showed a 20% increase in the Triton-insoluble cytoskeletal F-actin in cultures from hypothyroid brain relative to normal controls. In the Triton-soluble fraction, containing the G-actin and the noncytoskeletal F-actin, cultures from hypothyroid brain showed a 15% increase in G-actin, whereas the F-actin remained unaltered. The 10% increase in total actin observed in this fraction from hypothyroid brain could be totally accounted for by the enhancement of G-actin. The mean F-actin/G-actin ratio in this fraction was about 30% higher in the cultures from normal brain compared to that of the hypothyroid system, which indicates that hypothyroidism tends to decrease the proportion of noncytoskeletal F-actin relative to G-actin.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 10269-10274 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a simple Lanczos method for calculating rovibrational energy levels of a triatomic molecule from a kinetic energy operator (KEO) with the z axis perpendicular to the molecular plane. We use rotational basis functions which are linear combinations of symmetric top functions so that all matrix elements are real. For some molecules, coupling between rotation and vibration is less important if the z axis is chosen perpendicular to the molecular plane, but the singularities of the z-axis operator are more difficult to deal with than those of the commonly used y-axis operator. The KEO with z axis perpendicular to the plane also reduces the number of sums over vibrational indices required to evaluate Hamiltonian matrix-vector products. Using a new symmetry-adapted basis and the z-axis KEO we calculate rovibrational energy levels of H2O for high J values. Even at J=40 we do not observe the formation of fourfold clusters. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Morphological changes and the molecular mechanisms associated with the maturation of astrocytes were studied under normal and thyroid hormone-deficient conditions using long-term (30 days) primary cultures derived from the neonatal rat brain. Immunocytochemical staining of cells with a monoclonal antibody specific to glial fibrillary acidic protein demonstrated for the first time that, similar to their maturation in vivo, astrocytes maintained in normal serum-containing medium can undergo complete maturation involving two distinct stages of morphological differentiation (from radial glia to flat polygonal cells with epithelioid morphology and then to mature process-bearing cells with stellate morphology). Deficiency of thyroid hormone delays the first step and totally blocks the second stage of differentiation in the maturation process. Comparative staining of normal and thyroid hormone-deficient astrocytes with filamentous actin-specific fluorescein isothiocyanate-phalloidin and quantitation of the various forms of intracellular actin using an improved DNase I assay demonstrated that maturation of astroglial cells is associated with characteristic alterations in the level of cytoskeletal and non-cytoskeletal filamentous (F) actin. In particular, the maintenance of the epithelioid form of the hypothyroid astrocytes is associated with a progressive increase in the level of cytoskeletal F-actin and a concomitant decline in the level of non-cytoskeletal F-actin. Quantitation of actin mRNA by Northern blot analysis and studies on the rate of actin synthesis at various stages of differentiation showed that the initial transformation into the epithelioid form is associated with an increase in the rate of synthesis of actin and the expression of its mRNA, while the final transformation into the mature process-bearing form is correlated with a decline in these parameters. The results indicate that thyroid hormone plays an obligatory role in promoting the differentiation and maturation of astrocytes, and that during this process the hormone regulates the expression of actin and its intracellular organization in a way conducive to morphological differentiation.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 69 (1997), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The effect of thyroid hormones (THs) on the expression of actin gene during fetal human brain development and the period of sensitivity to the hormones have been investigated. Developmental profile of actin in the cytoskeletal (CSK) and noncytoskeletal (non-CSK) fractions in the fetal cerebra showed a pronounced rise in the level of CSK actin at weeks 17–19. Northern blot analysis also revealed a sharp rise in the level of actin mRNA at weeks 16–18, temporally coinciding with the period of rise of THs and peak expression of TH receptors in the fetal brain. In organ cultures of weeks 13–23 fetal cerebra, THs elicited a general stimulation of CSK proteins at all ages studied with a preferential effect on actin at weeks 17–19. During this period, THs also stimulated the rate of synthesis of actin. Kinetics of induction of actin by TH in the non-CSK and CSK fractions in organ cultures of week 17 fetal cerebra showed an increased level of actin in both fractions within 1 h. Subsequently (at 5 and 18 h), induction was evident only in the insoluble CSK fraction, suggesting an effect of the hormone on the intracellular distribution of actin between the soluble non-CSK fraction and the insoluble CSK fraction. Correspondingly, in cultures of week 17 fetal cerebra, THs elicited an increase in actin mRNA level within 30 min of hormonal exposure. The overall results suggest that THs regulate the expression of actin gene by stimulating the rate of synthesis as well as intracellular distribution of actin during the mid phase of the second trimester of gestation.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-6903
    Keywords: Tubulin ; glial fibrillary acidic protein ; gene expression ; human fetal brain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Developmental alterations in the expression of glial fibrillary acidic protein (GFAP) and α-tubulin were examined at the level of mRNA and protein in human fetal brain between weeks 13–23 of gestation. Except for a transient increase at week 15, GFAP expression in the cytoskeletal (CSK) fraction was low until week 17, when it increased steadily to week 23, corresponding to the phase of glial proliferation. The developmental profile of α-tubulin in the CSK fraction displayed a biphasic pattern, with an initial rise between weeks 13–16 coinciding with the early phase of neuroblast multiplication, and a second rise between weeks 17–23 corresponding to the phase of glial proliferation. No significant difference in the spatial distribution of α-tubulin was found in different region of brain but GFAP expression varied with a higher level in cerebellum than that in cerebrum at late midgestation.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-6903
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Plasma membranes from neuronal perikarya (N), protoplasmic astrocytes (A) and oligodendrocyies (O) of rat brains were analysed with respect to their protein and glycoprotein contents and specificities. SDS-polyacrylamide gel electrophoresis revealed a total number of 23, 17, and 17 major proteins in N, A, and O respectively. Periodate-Schiff's staining showed that approximately 40–60% of these proteins were glycoproteins. The reactivity of these glycoproteins to Con A and WGA was also studied. Selective iodination of whole cells followed by electrophoresis and autoradiography indicated that of the major proteins, only 25% of neuronal and 60% of astroglial and oligodendroglial membrane proteins were exposed outside the cell surface. The overall results suggest that membrane proteins of each of the three cell types studied here have characteristically different internal and external markers differing in size, glycoprotein content, and reactivity of the glycoproteins to lectins.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 53-54 (1983), S. 233-244 
    ISSN: 1573-4919
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Of the various eucaryotic tissues, where glutamine synthetase (GS) mRNA and its regulation have been investigated, the induction of GS by glucocorticoids in the embryonic chick retina represents one of the systems most extensively studied. GS mRNA was first identified at the polysomal level by immunochemical precipitation of fractionated polysomes containing nascent GS chains with anti-GS γ-globulin. The mRNA has been shown to be polyadenylated at the 3′ end; on this basis, it has been partially purified from embryonic chick retina as well as from N. Crassa by chromatography on oligo(dT)-cellulose or poly(U)-sepharose and translated in cell-free protein synthesizing systems derived from wheat germ. Hormonal regulation of GS activity studied in the embryonic retina, hepatoma tissue culture cells, or in other tissues is always shown to be mediated by GS mRNA. In the retina, hydrocortisone(HC) elicits an age-related and transcription-dependent induction of GS by enhancing the level of GS mRNA in the polysomes through an increased supply of this mRNA from the nucleus. Comparative studies of three inhibitors of transcription, viz. actinomycin D, leucanthone and proflavine on the induction of GS by HC indicate that the latter inhibits GS mRNA selectively and reversibly with minimal effects on other RNA synthesis. Since proflavine acts by competing with HC-receptor binding sites in the nuclei, further studies on its interaction with the retina genome are likely to help identify the DNA sequences involved in the GS induction. In bacteria, studies on the genetics and physiology of various mutants with lesions in the structural gene for GS show that the transcription of the GS gene (gln A) is regulated both positively and negatively by GS and the product of another gene gln F. Purification of GS mRNA to homogeneity cloning of its cDNA and development of assay systems for cell-free transcription of GS are other studies likely to advance our knowledge on GS mRNA and its regulation.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Bioscience reports 5 (1985), S. 643-648 
    ISSN: 1573-4935
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effect of T3 (triiodothyronine) on the induction of tubulin in hypothyroid developing rat brain has been examined using organ cultures of brains from late fetal, neonatal and postnatalrats. The neonatal brain displayed maximum sensitivity to T3. Hypothyroidism resulted in a 26% decline in the level of tubulin in the neonatal brain as opposed to a 5–15% decline in the fetal or postnatal brain. Exposure of the hypothyroi d neonatal brain to T3 for 2 h in culture led to a 61% rise in the level of tubulin in contrast to a 41% increase seen in the case of normal brain. Total protein synthesis was not significantly affected . The preferential decline of tubulin in the neonatal hypothyroid brain, its enhanced sensitivity to T3 compared to normal brain, and the coincidence of the period of sensitivity to that of brain maturation indicate that the regulation of the level of tubulin by T3 in the developing brain is a natural ontogenic phenomenon.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 265-272 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Numerical experiments with a nonlinear (λχ4) oscillator which has its harmonic frequency changing randomly with time reveal certain interesting features of its dynamics of quantum evolution. When λ = 0, the level populations are seen to oscillate. But, as the nonlinear coupling is switched on (λ 〉 0), a threshold is reached at λ = λc when the evolution is seen to be characterized by an abrupt transition dominantly to the highest available state of the unperturbed (initial) oscillator. It is shown that this transition probability is maximized at a particular value of λ. The time threshold for this transition decreases with increasing nonlinear coupling strength. The numerically obtained structures of the underlying quantum-phase spaces of the linear and nonlinear random oscillators are examined. Possible use of these results in a problem of chemical origin is explored. © 1997 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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