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  • 1
    Electronic Resource
    Electronic Resource
    Selective Effects of Neonatal Hypothyroidism on Monoamine Oxidase Activities in the Rat Brain (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 40 (1983), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Hypothyroidism of mild intensity was obtained with prenatal and neonatal submission of Long-Evans rats to an iodide-rich diet. Chronic daily administration of methimazole to iodide-supplemented Long-Evans pups or to iodine-deprived Charles-River rats through the first 29–30 days of age provoked severe hypothyroidism. Monoamine oxidase type A (MAO-A) and not type B (MAO-B) activity was consistently, although slightly (by approximately 20%), increased in the hypothyroid brain. Triiodothyronine (T3)-induced hyperthyroidism did not affect MAO activity. Replacement therapy with T3 did not normalize MAO-A activity in hypothyroidism. Methimazole displayed a competitive and reversible in vitro inhibition of MAO-A but not MAO-B activity. Although this effect was obtained at concentrations far higher than those estimated to reach the brain after a single injection of the goiterogen, the occurrence of accumulation processes in the metabolism-deficient hypothyroid neonate rs cannot be excluded. Thus, MAO-A activity might be either directly depressed during the goiterogenic treatment, or increased as the result of some kind of rebound effect after interruption of methimazole administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1983.tb08087.x
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  • 2
    Electronic Resource
    Electronic Resource
    Abstracts (1971)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 269 (1971), S. 385-494 
    Details
    ISSN: 1432-1912
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01003053
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    [3H]Tyramine binding: A comparison with neuronal [3H]-dopamine uptake and [3H]mazindol binding processes (1989)
    Springer
    Neurochemical research 14 (1989), S. 949-955 
    Details
    ISSN: 1573-6903
    Keywords: Tyramine binding ; mazindol binding ; dopamine uptake ; trace amines ; hypothyroidism ; receptor solubilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract [3H]Spiperone ([3H]SPI) binding sites in rat or bovine striata have been solubilized using CHAPS or digitonin detergents. Solubilized sites retained the binding characteristics of those in native membrane preparations. The same solubilized material, however, did not bind [3H]tyramine ([3H]PTA), thus indicating that [3H]PTA binding sites and DA receptors are different chemico-physical entities. In membrane preparations or crude synaptosomes obtained from the c.striatum of neonatally-rendered hypothyroid rats, when central DA-pathways are impaired, both [3H]PTA binding and [3H]DA uptake processes were markedly decreased, with no effect on [3H]mazindol ([3H]MAZ) binding, compared to euthyroids. Reserpine, a well-known inhibitor of DA-uptake into a variety of secretory vesicles, and a potent in vivo andin vitro inhibitor of [3H]PTA binding, did not affect the [3H]MAZ binding process. This further supported the suggestion that while [3H]PTA binding sites are almost totally associated with the vesicular transporter for DA, [3H]MAZ does label a site involved in the DA-translocation across the neuronal membrane. The latter process seems to be rather insensitive to thyroid hypofunction, when however the intracellular storage of DA might be consistently impaired. In conclusion, PTA might be well exploited as a marker of the DA vesicular transporter through its molecular characterization, whenever possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00965928
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  • 4
    Electronic Resource
    Electronic Resource
    Potent, extra-channel influence of several calcium-channel modulators on striatal binding of [3H]tyramine (1993)
    Springer
    Neurochemical research 18 (1993), S. 1125-1130 
    Details
    ISSN: 1573-6903
    Keywords: [3H]Tyramine binding ; vesicular markers ; Ca2+-channel modulators ; K+-channel antagonists ; Na+-channel agents ; dopamine carrier ; vesicle membrane energetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A number of Ca2+-, K+-, and Na+-channel modulators has been tested with respect to their effects on [3H]tyramine (TY) binding, as a putative marker for the vesicular dopamine (DA) transporter in striatal membrane preparations containing vesicle ghosts. Among organic Ca2+-channel modulators, the diphenylalkylamines tested consistently inhibited TY binding: the order of potency was prenylamine〉lidoflazine〉flunarizine〉cinnarizine, with Ki values of 0.1, 0.2, 0.5 and 1.2 μM, respectively. Low (up to 100 nM) concentrations of prenylamine did competitively inhibit TY binding, and higher concentrations provoked a mixed-type inhibition. Furthermore, LIGAND-analysis of competition curves revealed a high- and a low-affinity binding site for prenylamine and flunarizine. The TY binding process was also sensitive to selected K+- and Na+-channel modulators. Since several Ca2+-antagonists are known to affect H+-ATPase and the bioenergetics of catecholamine storage vesicles in chromaffin granules, thus affecting monoamine storage, the energy requirements for the formation of the TY/carrier complex were here assessed, assuming similarity between chromaffin granules and synaptic vesicles. TY binding, though not reflecting endovesicle-sequestered TY, was indeed strongly sensitive (with Ki coefficients in the fM or low nM range) to the dissipation of the vesicular transmembrane proton concentration (Δ pH), electrical (Δ Ψ), and proton electrochemical (Δ μH+) gradients, provoked by a number of specifically targeted agents. It is concluded that Ca2+-channel agents of the diphenylalkylamine group may directly affect striatal TY binding due to an extrachannel-regulated competition with TY for the vesicular carrier of DA, as well indirectly, by disruption of the transmembrane energization of the reserpine-sensitive carrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00978362
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  • 5
    Electronic Resource
    Electronic Resource
    The tyramine binding site in the central nervous system: An overview (1993)
    Springer
    Neurochemical research 18 (1993), S. 861-868 
    Details
    ISSN: 1573-6903
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The [3H]Tyramine (TY) binding site is proposed as a high affinity marker of the membrane carrier for dopamine (DA) in synaptic vesicles from DA-rich brain regions. Under precise assay conditions, there is neither a consistent association of TY with the neuronal, cocaine-sensitive DA transporter, nor with mitochondrial or microsomal targets. TY-labeled sites have a high affinity for selected toxins such as the Parkinsonian agent MPP+ (1-methyl-4-phenylpyridinium ion), or drugs such as diphenylalkylamine Ca2+-channel antagonists. The MPP+/TY site interaction, which in the striatum leads to depletion of vesicular DA, occurs in dopaminergic as well as in noradrenergic regions, though with different kinetic profiles. TY-labeled carriers for DA and noradrenaline (NA) in respective vesicles seem to be different entities, which might result in a region-specific rate of toxin sequestration and/or release from heterogeneous vesicles. Whereas MPP+ is a potent competitive-type inhibitor of [3H]TY binding, prenylamine-like Ca2+-channel antagonists can compete with TY for the vesicle site, in a tetrabenazine- or reserpine-like manner, and also inhibit TY binding thanks to the extra-channel directed impairment of membrane bioenergetics they are proposed to provoke. This follows from the generally-accepted assumption that similar mechanisms are operational for secretory organelles in adrenals and CNS, and from the marked sensitivity of TY binding to miscellaneous energy-disrupting agents. A model is therefore proposed, depicting the TY-, DA- or MPP+-labeled, vesicle carrier, as a dimeric protein which may switch from the cytoplasm-oriented, “recognition” state, to the vesicle-oriented, “transport” state, thanks to the establishment of an H+-ATPase-supported, membrane protein electrochemical gradient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00998269
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