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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The mechanism by which two D3 receptor-preferring agonists, 7-hydroxydipropylaminotetralin (7-OH-DPAT) and quinelorane, modulate cocaine reinforcement was examined by monitoring nucleus accumbens dopamine levels with in vivo microdialysis while rats intravenously self-administered the following four different drug solutions consecutively: (1) cocaine; (2) a combination of cocaine plus a low dose of either agonist; (3) either agonist alone; and finally, (4) a physiological saline solution. Both 7-OH-DPAT (4 µg/infusion) and quinelorane (0.25 µg/infusion) decreased cocaine (0.25 mg/infusion) intake in a manner indicating an enhancement of cocaine reinforcement and simultaneously decreased the cocaine-induced elevations in nucleus accumbens dopamine levels by 〉50%. Subsequent self-administration of either 7-OH-DPAT (4 µg/infusion) or quinelorane (0.25 µg/infusion) alone resulted in significant, but stable, increases in drug intake, with a concurrent decrease in nucleus accumbens dopamine levels to ∼50% below nondrug baseline levels. These findings indicate that postsynaptic D3 receptor stimulation in the nucleus accumbens enhances the reinforcing properties of cocaine. In a second experiment, local application of 7-OH-DPAT via reverse dialysis (30 and 100 nM perfusate concentrations) dose-dependently decreased nucleus accumbens dopamine efflux to 76 ± 3.9 and 61 ± 6.3% of baseline, respectively, whereas there was no effect of this agonist on dopamine efflux in the ipsilateral striatum of these same animals. Coperfusion with the D3 receptor-preferring antagonist nafadotride dose-dependently blocked the effect of 7-OH-DPAT on nucleus accumbens dopamine efflux. These results suggest that, at low concentrations, 7-OH-DPAT selectively activates D3 receptors in vivo.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4596-4607 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bi2Sr2Ca0.64Cu1.64Ox (nominally Bi2212) powders were fabricated into powder-in-tube Ag- and Ag(7 at. % Cu)-sheathed tapes by cold and hot rolling to investigate the effects of sheath composition and rolling conditions on their microstructural development and superconducting properties. Bi2212 tapes with Ag(Cu) sheaths exhibited improved grain alignment and interfacial uniformity, as well as enhanced formation of the Bi-free phase (≈Sr7.5Ca6.5Cu14Ox), relative to the Ag-sheathed specimens. The hot-rolled Ag(Cu)-sheathed tapes displayed superior critical current densities (Jc), where magnetization Jcm=1.5×106 (H(parallel)c) and 4.6×105 A/cm2 (H⊥c) at T=5 K, H=1 T. Correspondingly, these specimens had transport critical current densities (Jct) of 6.7×104 A/cm2 (H(parallel)c) and 5.4×104 A/cm2 (H⊥c) at T=4.2 K, H=0 T and 2.2×104 A/cm2 (H(parallel)c) and 3.0×104 A/cm2 (H⊥c) at T=4.2 K, H=14 T. The chemical stability of the Ag(Cu) sheath regions during the partial melting process was also studied. Rapid oxidation of copper produced Cu2O precipitates in the sheath at 885 °C, and subsequently a Cu2O-free zone developed near the core/sheath interface. A theoretical analysis of Cu2O precipitate formation and decomposition during thermal processing is presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6567-6567 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The study of the thermal conductivity of high temperature superconductors can provide a theoretical understanding of the nature of the charge carriers, phonons, and scattering processes between them. From the technological point of view, thermal conductivity influences the growth rate of a local hot spot in a superconductor and therefore it is an important parameter in thermal stability analysis. Recently, the magnetothermal conductivity has been considered to be a key factor in the understanding of the vortex mechanisms. Here we report thermal conductivity measurements of bulk Bi2Sr2CanCun+1Ox superconductors in an applied magnetic field up to 20 T. The measurements are taken with field directions both parallel and perpendicular to the a-b plane of the samples for a wide range of temperatures. The phonon scattering mechanism at vortex sites, thermal transport mechanism in both a-b and c directions, as well as across grain boundaries will be discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4931-4933 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetothermal conductivity of high-temperature superconductors (HTS) reflects the scattering processes between the charge carriers, phonons, and vortices. Therefore, the magnetothermal conductivity can provide information about the vortex dynamics. Here, we report thermal conductivity measurements of bulk Bi2Sr2CaCu2Ox superconductors in an applied magnetic field up to 20 Tesla. The measurements were taken over a wide range of temperatures around Tc. The superconducting parameters were successfully recovered from the obtained data using the theoretical model developed by Ausloos and Houssa [J. Phys. Condens. Matter 7, 193 (1995)], in which the change in thermal conductivity in the applied magnetic field is predominantly due to the scattering between the vortex lines in the superconductor and the normal electrons in the Cu–O planes. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The anomalous behavior of the thermal conductivity, κ, of high temperature superconductors (HTS) has been attributed to two conflicting theories (phonon domination and electron domination) since the discovery of HTS. Change in κ due to a magnetic field is a direct consequence of additional scattering processes between the phonons, the charge carriers, and the flux lines. The existing theories predict different scattering effects for the phonons and the electrons. Therefore, knowing magnetothermal conductivity can provide useful information for the nature of heat carriers in HTS and the understanding of the vortex dynamics. We have measured the in-plane thermal conductivity of a c-axis aligned Bi2Sr 2CaCu2Ox superconductor in magnetic fields up to 17 T. The magnetic field was applied both parallel and perpendicular to the c axis and always perpendicular to the direction of heat flow. The results are compared to existing electronic and phononic models. It has been discovered that the electronic thermal conductivity, κe, calculated from the Wiedemann–Franz law, does not predict the measured behavior of the thermal conductivity. Rather, the phonon thermal conductivity, κph, calculated from the extended BRT (Bardeen, Richayzen, and Tewordt) theory, reproduces the experimental results accurately. The anisotropy of the in-plane magnetothermal conductivity is also investigated. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 19 (1972), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Administration of l-histidine at the rate of 500 mg/kg induced an increase of nearly 50 per cent in the level of histamine in rat brain which lasted several hours. The augmentation of histamine level was not significant 3 h after lower doses or after d-histidine α-methyl DOPA and Ro 4-4602 neither affected the cerebral level of histamine nor its elevation induced by l-histidine. Brocresine, a known histidine decarboxylase inhibitor not only prevented the effect of histidine load but also induced a prompt fall in the amine level. These results confirm those from earlier experiments in vitro indicating that histamine synthesis in rat brain depends on a specific decarboxylase (EC 4, 1.1.22) which is not normally saturated by the endogenous level of its substrate.When histamine levels were enhanced by histidine treatment, histidine decarboxylase activity, as evaluated on hypothalamus homogenates, was significantly reduced; intracisternal administration of cycloheximide, an inhibitor of protein synthesis, had similar effects. On the other hand, enzyme activity was not altered by the addition of histamine to hypothalamus homogenates. These results are compatible with the existence of a regulation mechanism of histidine decarboxylase involving repression by its end-product.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 20 (1973), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The mechanism of histamine methyltransferase (HMT) inhibition by S-adenosylhomocysteine (SAH) has been investigated on a partially purified enzyme from guinea-pig brain. The kinetic data indicated that this inhibition was competitive with respect to S-adenosylmethionine (SAMe) and noncompetitive with respect to histamine. The Kt, values (about 5 ± 10−6 M in both cases) indicated that SAH had a higher affinity than SAHe or histamine for the enzyme.In rats, after administration of a small dose of SAH, methylation of intracisternally injected [3H]histamine was not modified.However, treatment with l-DOPA or pyrogallol induced a decrease in [3H]histamine methylation, presumably due to a modification in the SAMe/SAH ratio in the brain. Hence, histamine methylation in brain could be regulated according to the value of this ratio and thus related to methylation of other biogenic amines.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 17 (1970), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: —Properties of the histamine-forming enzyme in rat brain were studied, utilizing a sensitive fluorometric assay. The optimum pH was related to substrate concentration and found to be6·4 at 10−2m-histidine; the apparent Km was about 4·10−4m; enzyme activity was inhibited by α-hydrazino -histidine and brocresine but was not affected by α-methyl DOPA or benzene. These different data suggest that the 'specific’histidine decarboxylase (EC 4.1.1.22)—and not the aromatic l-aminoacid decarboxylase—is involved. Determination of enzyme activity and histamine level in different areas of the rat brain revealed important regional differences, the two values being roughly parallel.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 21 (1973), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The subcellular distribution of histidine decarboxylase (assayed by two different isotopic methods) and several biochemical markers (lactate dehydrogenase, DOPA decarboxylase and protein) was determined in rat cerebral cortex. After differential centrifugation, the enzyme activity was found mainly in the crude mitochondrial and soluble fractions. Further separation of the former on discontinuous sucrose gradients showed that the particulate histidine decarboxylase (HD) was found in the synaptosomal fraction. After osmotic shock, HD activity appeared in the supernatant fraction suggesting that a major portion of the enzyme is localized in the cytoplasm of cortical nerve endings. By analogy with other brain amines, this finding, together with the presence of histamine in synaptic vesicles (Kataoka and de Robertis, 1967), can be taken as further support for the hypothesis of a role as neurotransmitter for histamine.Various brain regions were homogenized under conditions leading to synaptosome formation. The distribution of HD between ‘particulate’ and soluble fractions differed from one region to the other, but did not give any clear-cut indication of regions rich in cell bodies or nerve terminals.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 18 (1971), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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