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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 22 (1997), S. 181-187 
    ISSN: 1573-6903
    Keywords: Glutamate ; [3H]glutamate-binding ; guanine nucleotides ; adenylate cyclase ; G-proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract GMP-PNP, a non-hydrolyzable analog of GTP binds tightly to G-protein in the presence of Mg2+, so that the binding is stable even after exhaustive washings. This property was exploited to prepare membrane samples of rat brain where G-protein GTP-binding sites were saturated with GMP-PNP. Experiments carried out with these membranes showed that GTP, GMP-PNP, GDP-S and GMP (1 mM) inhibit the sodium-independent [3H]glutamate binding by 30–40% [F(4,40) = 5.9; p 〈 .001], whereas only GMP-PNP activates adenylate cyclase activity [F(6,42) = 3.56; p 〈 .01]. The inhibition of sodium-independent [3H]glutamate binding occurred in the absence of Mg2+. These findings suggest that guanine nucleotides may inhibit glutamate binding and activate adenylate cyclase through distinct mechanisms by acting on different sites.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 24 (1999), S. 1067-1074 
    ISSN: 1573-6903
    Keywords: Adenosine A2 receptors ; NECA binding ; guanine nucleotides ; glutamate analog ; cAMP ; chicks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Binding properties of the subtypes of adenosine A2 receptors in membrane preparations and the effects of adenosine receptor ligands on cAMP accumulation in slices from the optic tectum of neonatal chicks have been investigated. [3H]2-[4-(2-p-carboxyethyl)phenylamino]-5'-N-ethylcarboxaminoadenosine (CGS 21680), a selective ligand for adenosine A2a receptors, did not bind to optic tectal membranes, as observed with rat striatal membranes. CGS 21680 also did not induce cyclic AMP accumulation in optic tectum slices. However, 5'-N-ethylcarboxamidoadenosine (NECA), 2-chloro-adenosine or adenosine induced a 2.5- to 3-fold increase on cyclic AMP accumulation in this preparation. [3H]NECA binds to fresh non-washed-membranes obtained from optic tectum of chicks, displaying one population of binding sites, which can be displaced by NECA, 8-phenyltheophylline, 2-chloro-adenosine, but is not affected by CGS 21680. The estimated KD value was 400.90 ± 80.50 nM and the Bmax was estimated to be 2.51 ± 0.54 pmol/mg protein. Guanine nucleotides, which modulate G-proteins activity intracellularly, are also involved in the inhibition of glutamate responses by acting extracellularly. Moreover, we have previously reported that guanine nucleotides potentiate, while glutamate inhibits, adenosine-induced cyclic AMP accumulation in slices from optic tectum of chicks. However, the guanine nucleotides, GMP or GppNHp and the metabotropic glutamate receptors agonist, 1S,3R-ACPD did not alter the [3H]NECA binding observed in fresh non-washed-membranes. Therefore, the adenosine A2 receptor found in the optic tectum must be the adenosine A2b receptor which is available only in fresh membrane preparations, and its not modulated by guanine nucleotides or glutamate analogs.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 24 (1999), S. 1037-1042 
    ISSN: 1573-6903
    Keywords: Lead acetate ; adenylate cyclase ; 5′-guanylylimidodiphosphate ; forskolin ; cerebral cortex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Lead decreased in a dose dependent manner the basal AC activity in membranes of rat cerebral cortex (IC50 = 2.5 ± 0.1 μM). In membranes preincubated under basal conditions, AC activity was stimulated by approximately two and fourfold by 10 μM Gpp(NH)p or forskolin, respectively. Under basal conditions, lead (3 μM) inhibited enzyme activity up to 50%, but was not able to inhibit the Gpp(NH)p- or the forskolin-stimulated AC activity. However, in membranes preincubated with Gpp(NH)p (10 μM), lead (3 μM) had no significant effect on enzyme activity, but it partly blocked the stimulation of AC activity elicited by forskolin (10 μM). In membranes preincubated with 10 μM lead, the addition of 10 μM Gpp(NH)p or forskolin in the incubation medium did not stimulate AC activity. However, when added together in the incubation medium Gpp(NH)p + forskolin produced an increase in enzyme activity. In membranes preincubated with 10 μM lead + 10 μM Gpp(NH)p, Gpp(NH)p (10 μM) or forskolin (10 μM) added alone or in combination to the incubation medium did not stimulate AC activity. Moreover, under these latter conditions lead had no further effect on enzyme activity. These results indicate that lead may interact with G-proteins and with the catalytic subunit of cerebral cortical AC to produce inhibition of the enzyme activity.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 25 (2000), S. 181-188 
    ISSN: 1573-6903
    Keywords: Adenosine ; guanine nucleotides ; GMP ; adenosine A2 receptors ; glutamate ; hippocampus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Guanine nucleotides (GN) have been implicated in many intracellular mechanisms. Extracellular actions, probably as glutamate receptor antagonists, have also been recently attributed to these compounds. GN may have a neuroprotective role by inhibiting excitotoxic events evoked by glutamate. Effects of extracellular GN on adenosine-evoked cellular responses have also been reported. However, the exact mechanism of such interaction is not known. In the present study, we showed that GN potentiated adenosine-induced cAMP accumulation in slices of hippocampus from young rats. However, neither GMP nor the metabotropic glutamate receptor agonist, 1S,3R-ACPD, inhibited the binding of the adenosine receptor agonist [3H]NECA (when binding to adenosine A2 receptors), or the binding of the adenosine A2a receptor agonist [3H]CGS 21680 in hippocampal membrane preparations. GppNHp, probably by interacting with G-proteins, decreased [3H]CGS 21680 binding. [3H]GMP binding was assayed in order to evaluate the GN sites which are not G-proteins. [3H]GMP binding was inhibited by GMP and GppNHp, but not by 1S,3R-ACPD. The interaction of endogenous adenosine with the GMP-binding sites was determined by incubating membranes in the presence or absence of adenosine deaminase (ADA). NECA, CADO, CGS 21680 and CPA (only at the highest concentration used) increased GMP binding in the presence of ADA. However, in the absence of ADA, the control levels of GMP binding were as high as in the presence of added ADA plus adenosine agonists, indicating that endogenous adenosine modulates the binding of GMP. If this site has a neuroprotective role, adenosine may be increasing its neuromodulator and proposed protective action.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 25 (2000), S. 211-215 
    ISSN: 1573-6903
    Keywords: Glutamate ; guanine nucleotides ; antinoception ; naturally-occurring compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Glutamate is to be considered a nociceptive neurotransmitter and glutamatergic antagonists present antinoceptive activity. In this study we investigated the effects of the naturally occurring antinociceptive compounds rutin, geraniin and quercetine extracted from Phyllanthus, as well as the diterpene jatrophone, extracted from Jatropha elliptica on the binding of [3H]glutamate and [3H]GMP-PNP [a GTP analogue which binds to extracellular site(s), modulating the glutamatergic transmission] in rat brain membrane. Jatrophone inhibited [3H]glutamate binding and geraniin inhibited [3H]GMP-PNP binding. Quercetine inhibited the binding of both ligands. These results may indicate a neurochemical parameter possibly related to the antinoceptive activity of these natural compounds.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 22 (1997), S. 1507-1510 
    ISSN: 1573-6903
    Keywords: Glutamate ; binding ; anticonvulsant ; γ-decanolactone ; epilepsy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Epilepsy is one of the most common neurological disorders. Even though antiepileptic drugs can afford a reasonably satisfactory treatment for 80% of diagnosed patients, chronic intractable epilepsy still affects a significant number of people and more effective and less harmful antiepileptic drugs are needed. Previous studies have shown that γ-decanolactone has dose-dependent sedative effects, including hypnotic, anticonvulsant and hypothermic properties in mice. The present study reports an inhibitory effect of γ-decanolactone on glutamate binding (96.8% with 5 mM) in rat cortex membranes. The non competitive nature of glutamate binding inhibition as a neurochemical correlate of the anticonvulsant activity of γ-decanolactone may be a relevant mode of action for further drug development.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 23 (1998), S. 519-524 
    ISSN: 1573-6903
    Keywords: Glutamate ; excitotoxicity ; rat hippocampus ; guanine nucleotides ; reactive oxygen species ; chemiluminescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Glutamate significantly increased levels of spontaneous chemiluminescence (CL) in rat hippocampal slices incubated under hypoxic conditions. Although it has been previously shown that guanine nucleotides (GN) displace glutamate from several of its receptors, in our study only GMP, as well as the glutamate antagonist MK-801, was able to reverse the increase in CL provoked by glutamate. On the other hand, not only GTP or Gpp(NH)p failed to reverse the action of glutamate, but they increased CL production like glutamate. This effect of GTP/Gpp(NH)p was also reversed by GMP. We concluded that, under neurotoxic conditions, GMP acted as an antagonist and GTP or Gpp(NH)p acted as agonists of glutamate. These results reinforced the evidence of the existence of extracellular site(s) for GN and indicated a possible role for GN in excitotoxicity.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 20 (1995), S. 1437-1441 
    ISSN: 1573-6903
    Keywords: Pyroglutamic acid ; organic acidemias ; neurotoxicity ; adenylate cyclase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect ofl-pyroglutamic acid, a metabolite that accumulates in pyroglutamic aciduria, on different neurochemical parameters was investigated in adult male Wistar rats. Glutamate binding, adenylate cyclase activity and G protein coupling to adenylate cyclase were assayed in the presence of the acid.l-pyroglutamic acid decreased Na+-dependent and Na+-independent glutamate binding Basal and GMP-PNP stimulated adenylate cyclase activity were not affected by the acid. Furthermore, rats received unilateral intrastriatal injections of 10–300 nmol of bufferedl-pyroglutamic acid. Vehicle (0.25 M Tris-Cl, pH 7.35–7.4) was injected into the contralateral striatum. Neurotoxic damage was assessed seven days after the injection by histological examination and by weighing both cerebral hemispheres. No difference in histology or weight could be identified between hemispheres. These results suggest that, although capable of interfering with glutamate binding, pyroglutamate did not cause a major lesion in the present model of neurotoxicity.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 20 (1995), S. 461-465 
    ISSN: 1573-6903
    Keywords: Glutamate ; anticonvulsant ; Linalool ; binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Linalool is a monoterpene compound reported to be a major component of essential oils in, various aromatic species. Several Linalool-producing species are used in traditional medical systems, includingAeolanthus suaveolens G. Dom (Labiatae) used as anticonvulsant in the Brazilian Amazon. Psychopharmacological in vivo evaluation of Linalool showed that this compound have dose-dependent marked sedative effects at the Central Nervous System, including hypnotic, anticonvulsant and hypothermic properties. The present study reports an inhibitory effect of Linalool on Glutamate binding in rat cortex. It is suggested that this neurochemical effect might be underlining Linalool psychopharmacological effects. These findings provide a rational basis for many of the traditional medical use of Linalool producing plant species.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 23 (1998), S. 183-188 
    ISSN: 1573-6903
    Keywords: Glutamate ; 1S,3R-ACPD ; guanine nucleotides ; mGluRs (metabotropic glutamate receptors)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Metabotropic glutamate receptors (mGluRs) have been shown to modulate adenylate cyclase activity via G-proteins. In the present study we report similar results to the previously observed in the literature, showing that glutamate and the metabotropic agonists, 1S,3R-ACPD or quisqualate induced cAMP accumulation in hippocampal slices of young rats. Moreover, guanine nucleotides GTP, GDP or GMP, inhibited the glutamate-induced cAMP accumulation. By measuring LDH activity in the buffer surrounding the slices, we showed that the integrity of the slices was maintained, indicating that the effect of guanine nucleotides was extracellular. GMP, GDPβ-S or Gpp(NH)p abolished quisqualate-induced cAMP accumulation. GDPβ-S or Gpp(NH)p but not GMP inhibited 1S,3R-ACPD-induced cAMP accumulation. The response evoked by glutamate was also abolished by the mGluR antagonists: L-AP3 abolished glutamate-induced cAMP accumulation in a dose-dependent manner and MCPG was effective only at the 2 mM dose. DNQX was ineffective. We are reporting here, an inhibition induced by guanine nucleotides, via an extracellular site (s), similar to the observed with classical glutamate antagonists on a cellular response evoked by mGluR agonists.
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