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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 64 (1992), S. 1790-1794 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 66 (1994), S. 2017-2021 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The height of peak 2, h2, recorded using linear sweep voltammetry with 350-μm-diameter carbon paste electrodes in rat striatum was measured from the day of implantation (day 0) to 4 months after surgery. The value of h2was at a minimum on day 0 (0.6 ± 0.2 nA; n = 20), rose sharply to a maximum on day 2 (6.3 ± 0.9 nA; n = 12), and decreased to a stable level by day 7 (3.3 ± 0.7 nA; n = 16), which lasted for 4 months (3.2 ± 0.6 nA; n = 9). These changes were shown by microinfusion of uricase to be due to variations in the concentration of extracellular uric acid, although h2 appears to have a small baseline contribution of ∼0.3 nA from 5-hydroxyindoleacetic acid. The stable value of h2 recorded under chronic conditions was estimated to correspond to a minimal uric acid concentration of 50 μmol/ L, which represents a 10-fold increase in the extracellular level of this purine metabolite compared with the initial (acute) value. Very similar results were obtained using a mi-crodialysis technique that detected uric acid directly. These estimates of striatal uric acid concentration are in marked contrast to those obtained using 40-μm diameter carbon fiber electrodes, which showed a decrease from the acute preparation to 〈 1 μmol/L under chronic conditions. Large values of h2 were also recorded with chronically implanted paste electrodes in the hippocampus and frontal cortex. The results suggest that large in vivo probes, such as carbon paste electrodes and dialysis tubes, markedly disturb the neurochemical balance in the extracellular fluid even 1 day following implantation and emphasize the need to develop further small sensors for in vivo neurochemical analysis with minimal perturbation.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We have used a glucose oxidase-based sensor implanted in the striatum of freely moving rats to determine the concentration of extracellular glucose in two distinct ways. With a modification of the zero net flux method, in which different concentrations of glucose are infused through a dialysis probe glued to the biosensor, we calculated the concentration at which there was no change in glucose current by regression analysis; this gave a concentration of 0.351 ± 0.016 mM. Calculating the concentration from the basal current and the in vitro calibration of the biosensor was not significantly different from this. The basal extracellular glucose concentration determined by either method remained constant over a period of several days. Infusion of 50 µM veratridine through the adjacent dialysis probe caused a steep decrease in glucose current as soon as the drug reached the brain in contrast to the delayed fall (7.5 min) seen with microdialysis in previous experiments from this laboratory. These results demonstrate that this biosensor provides a direct, real-time measure of the extracellular concentration of glucose.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 7 (1995), S. 0 
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Microdialysis was used in the freely moving rat to measure the effects of graded changes in brain glucose on the serotonergic and noradrenergic projections to the hippocampus. The concentration of glucose in the dialysate was monitored using an enzyme-based assay. A systemic injection of insulin caused a steep decline in glucose level which was restored to the control level by oral administration of glucose solution. The changes in 5-hydroxytryptamine (5-HT) and noradrenaline were a mirror image of the glucose changes: they rose after insulin injection and returned to control during glucose administration. A delayed increase was shown by 5-hydroxyindoleacetic acid (5-HIAA) which did not return to baseline on glucose administration. The metabolite dihydroxyphenylacetic acid (DOPAC) decreased after insulin administration and increased above control during glucose administration. While the responses of 5-HT, noradrenaline and 5-HIAA to hypoglycaemia resemble those to mild stress, the changes in DOPAC are the reverse of those produced by stress.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 3 (1991), S. 0 
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We have used the techniques of microdialysis and in vivo voltammetry to monitor striatal dopamine and ascorbate, as well as motor activity in unanaesthetized, freely-moving rats. Systemic administration of the non-selective dopamine receptor agonist apomorphine (0.5 mg/kg, s.c.) caused a decrease in dopamine, an increase in ascorbate, stereotyped behaviour and a generalized increase in motor activity. Separate systemic applications of the D2 receptor agonist SKF 38393 (10 mg/kg, s.c.) and the D2 receptor agonist Quinpirole (0.1 mg/kg s.c.) caused a decrease in dopamine but had no effect on ascorbate or motor activity. After coadministration of these drugs, there was an increase in both ascorbate and motor activity. Local application of apomorphine (0.01 mM) caused a reduction in dopamine similar to that seen following systemic application but had no effect on ascorbate or motor activity. The present results demonstrate that dopamine, via D1 and D2 receptors outside the striatum, plays an important role in the control of ascorbate release. These results lend further support to the hypothesis that changes in ascorbate levels are an index of glutamatergic neurotransmission.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-2072
    Keywords: Diazepam ; Tail-pinch ; Ascorbate ; Voltammetry ; Eating ; Ro15 1788 ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of diazepam on spontaneous and tailpinch-induced behaviour was monitored together with the measurement of extracellular ascorbate using constant potential voltammetry with carbon paste electrodes. Diazepam (3 mg/kg) was followed by eating during the 1st hour after administration in non-food-deprived rats and a reduction in the behaviour triggered by a mild tail-pinch 90 min after drug administration. There was no change in ascorbate concentration in parallel with the spontaneous eating; however, the brisk increase in ascorbate concentration in striatum, nucleus accumbens and hippocampus, which accompanies the tail-pinch, was decreased in size and duration after diazepam. This effect was blocked by the central benzodiazepine receptor antagonist Ro15 1788 (5 mg/kg).
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Chicester [u.a.] : Wiley-Blackwell
    Journal of Molecular Recognition 9 (1996), S. 664-671 
    ISSN: 0952-3499
    Keywords: sensor ; glucose ; lactate ; microelectrode ; microdialysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Amperomeric-based detectors have successfully been used as personal monitors for blood glucose levels. However, there is a desire to increase the number of compounds measured in a small blood sample, the speed of detection and enhance the reliability of the measurement. Furthermore, with the increasing use of microdialysis as a clinical sampling method in metabolic medicine, paediatric medicine and neurointensive care, there is a need for rapid on-line detection of analytes such as lactate, glucose and glutamate in low microlitre volume samples.Two approaches to these problems are described. The first uses enzymes immobilized in a packed bed with electrochemical detection of a ferrocene mediator as a flow-injection assay for use with microdialysis. Results from microdialysis of the brain of freely moving rats are described. In the second approach, thin-film techniques are used to fabricate arrays of microdisk and micro line electrodes. The properties of these arrays in free solution and in a flow cell are presented together with an example using multiple arrays to identify an analyte by oxidation potential. Finally, different enzymes are entrapped onto the surface of two arrays by electrochemical polymerization of o-phenylenediamine. The resulting device detects glucose and lactate in real-time.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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