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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6328-6336 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new Monte Carlo approach which is capable to reduce significantly the two-phase coexistence region by constraining the system to remain fairly homogeneous in the transition region. This is achieved by introducing the chemical potential as an extra intensive thermodynamic variable in the canonical average. The technique developed was applied in a system containing 224 hard disks. The approach can, on the other hand, be applied in a general way to other systems.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 186 (1960), S. 147-148 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Attempts to sample the materials from different layers by means of suitable tools held in a micro-manipulator were unsuccessful and some of the layers were too thin for the application of micro-drilling techniques1'2. Experiments using a carbon extraction replica technique were also unsuccessful, ...
    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 106 (1997), S. 7856-7861 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Geometrical effects on folding of macromolecules are investigated using linear chains with tetrahedral structure and hard-core interactions among its monomers; extra self-avoidance, namely, nontopological neighbor, is also considered. Our results were obtained by exact calculations using chains with small number N of monomers (up to 16) and by Monte Carlo simulation, using the ensemble growth method (EGM), for larger N. For some cases we provide a comparative study using two types of lattice and three different models. The original number of angle choices, ζ=3 (coordination number), is shown to be effectively reduced to ζeff=2.760, and the radius of gyration and end-to-end distance, for finite chains (N≤140), scales with the number of monomers as Nν, where ν≅2/3. This is significantly larger than the corresponding value for the self-avoiding walk model, ν≅0.6. The relative frequency of monomer pair contacts was obtained by the exact Gibbs ensemble, involving all possible configurations. The same calculation using the EGM reveals ergodic difficulties; its significance on the setting up of pathways for folding of macromolecules is discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 243-247 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: GH3 cells present spontaneous Ca2+ action potentials and oscillations of intracellular Ca2+, which can be modified by altering the activity of K+ or Ca2+ channels. We took advantage of this spontaneous activity to screen for effects of a purified toxin (Tx3-1) from the venom of Phoneutria nigriventer on ion channels. We report that Tx3-1 increases the frequency of Ca2+ oscillations, as do two blockers of potassium channels, 4-aminopyridine and charybdotoxin. Whole-cell patch clamp experiments show that Tx3-1 reversibly inhibits the A-type K+ current (IA) but does not block other K+ currents (delayed-rectifying, inward-rectifying, and large-conductance Ca2+-sensitive) or Ca2+ channels (T and L type) in these cells. In addition, we describe the sequence of a full cDNA clone of Tx3-1, which shows that Tx3-1 has no homology to other known blockers of K+ channels and gives insights into the processing of this neurotoxin. We conclude that Tx3-1 is a selective inhibitor of IA, which can be used to probe the role of this channel in the control of cellular function. Based on the effect of Tx3-1, we suggest that IA is an important determinant of the frequency of Ca2+ oscillations in unstimulated GH3 cells.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The effectiveness of intranasal drug administration to stimulate central neuronal systems is well known from drug addiction and has also been considered as an alternative pharmacokinetic approach to treat brain disorders such as Parkinson's disease. In the present study, the possible neurochemical effects of intranasal administration of the psychostimulants cocaine and amphetamine and of the antiparkinsonian drug l-DOPA were analyzed. By using in vivo microdialysis in the urethane-anesthetized rat, it was found that unilateral intranasal administration of either of the psychostimulants led to huge and rapid increases of extracellular dopamine levels in the neostriatum followed by decreases of its metabolites dihydroxyphenylacetic acid and homovanillic acid. Furthermore, intranasal administration of l-DOPA, but not of the saline vehicle, also led to increased extracellular levels of neostriatal dopamine and to increases of its metabolites. Because the effect of intranasal l-DOPA on neostriatal dopamine was observed only ipsilaterally but not contralaterally to the side of intranasal drug administration, it can be hypothesized that l-DOPA was not effective via passage through the circulation but may have acted through a neuronal or an extraneuronal route. These data provide neurochemical evidence that the intranasal route may not only be efficient in drug abuse, but may also be useful to target the brain therapeutically, as in the case of neurodegenerative brain disorders.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Histamine has been implicated, inter alia, in mechanisms underlying arousal, exploratory behaviour and emotionality. Here, we investigated behavioural and neurochemical parameters related to these concepts, including open-field activity, rotarod performance and anxiety, as well as brain acetylcholine and 5-HT concentrations of mice deficient for the histidine decarboxylase (HDC) gene. These mice are unable to synthesize histamine from its precursor histidine. The HDC-knockout mice showed reduced exploratory activity in an open-field, but normal habituation to a novel environment. They behaved more anxious than the controls, as assessed by the height–fear task and the graded anxiety test, a modified elevated plus-maze. Furthermore, motor coordination on the rotarod was superior to controls. Biochemical assessments revealed that the HDC-knockout mice had higher acetylcholine concentrations and a significantly higher 5-HT turnover in the frontal cortex, but reduced acetylcholine levels in the neostriatum. These results are suggestive of important interactions between neuronal histamine and these site-specific neurotransmitters, which may be related to the behavioural changes found in the HDC-deficient animals.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Gap-junction channels in the brain, formed by connexin (Cx) proteins with a distinct regional/cell-type distribution, allow intercellular electrical and metabolic communication. In astrocytes, mainly the connexins 43, 26 and 30 are expressed. In addition, connexin30 is expressed in ependymal and leptomeningeal cells, as well as in skin and cochlea. The functional implications of the astrocytic gap-junctional network are not well understood and evidence regarding their behavioural relevance is lacking. Thus, we have tested groups of Cx30−/−, Cx30+/−, and Cx30+/+ mice in the open-field, an object exploration task, in the graded anxiety test and on the rotarod. The Cx30−/− mice showed reduced exploratory activity in terms of rearings but not locomotion in the open-field and object exploration task. Furthermore, Cx30−/− mice exhibited anxiogenic behaviour as shown by higher open-field centre avoidance and corner preference. Graded anxiety test and rotarod performance was similar across groups. The Cx30−/− mice had elevated choline levels in the ventral striatum, possibly related to their aberrant behavioural phenotypes. The Cx30+/− mice had lower dopamine and metabolite levels in the amygdala and ventral striatum and lower hippocampal 5-hydroxyindole acid (5-HIAA) concentrations relative to Cx30+/+ mice. Furthermore, the Cx30+/− mice had lower acetylcholine concentrations in the ventral striatum and higher choline levels in the neostriatum, relative to Cx30+/+ mice. Our data suggest that the elimination of connexin30 can alter the reactivity to novel environments, pointing to the importance of gap-junctional signalling in behavioural processes.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The present work tested whether pharmacological activation of protein kinase C (PKC) influences the release of [3H]-acetylcholine ([3H]ACh) synthesized in the presence of vesamicol, an inhibitor of the vesicular acetylcholine transporter (VAChT). Newly synthesized [3H]ACh was released from hippocampal slices by field stimulation (15 Hz) in the absence of vesamicol, but as expected [3H]ACh synthesized during exposure to vesamicol was not released significantly by stimulation. Treatment of slices with the PKC activator phorbol myristate acetate (PMA) decreased the inhibitory effect of vesamicol on [3H]ACh release. The effect of PMA was dose-dependent, was sensitive to calphostin C, a PKC-selective inhibitor, and could not be mimicked by α-PMA, an inactive phorbol ester. PMA did not alter the release of [3H]ACh in the absence of vesamicol, suggesting that the site of PKC action could be related to the VAChT. In agreement with this observation, immunoprecipitation of VAChT from 32P-labeled synaptosomes showed that phosphorylation occurs and that incorporation of 32P in the VAChT protein increases in the presence of PMA. We suggest that PKC alters the output of [3H]ACh formed in the presence of vesamicol and also provide circumstantial evidence for a role of phosphorylation of VAChT in this process.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 60 (1995), S. 5291-5294 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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