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  • 1
    Electronic Resource
    Electronic Resource
    SKF83959 selectively regulates phosphatidylinositol-linked D1 dopamine receptors in rat brain (2003)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 85 (2003), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Previously a distinct D1-like dopamine receptor (DAR) that selectively couples to phospholipase C/phosphatidylinositol (PLC/PI) was proposed. However, lack of a selective agonist has limited efforts aimed at characterizing this receptor. We characterized the in vitro and in vivo effects of SKF83959 in regulating PI metabolism. SKF83959 stimulates (EC50, 8 µm) phosphatidylinositol 4,5-biphosphate hydrolysis in membranes of frontal cortex (FC) but not in membranes from PC12 cells expressing classical D1A DARs. Stimulation of FC PI metabolism was attenuated by the D1 antagonist, SCH23390, indicating that SKF83959 activates a D1-like DAR. The PI-linked DAR is located in hippocampus, cerebellum, striatum and FC. Most significantly, administration of SKF83959 induced accumulations of IP3 in striatum and hippocampus. In contrast to other D1 DAR agonists, SKF83959 did not increase cAMP production in brain or in D1A DAR-expressing PC12 cell membranes. However, SKF83959 inhibited cAMP elevation elicited by the D1A DAR agonist, SKF81297, indicating that the compound is an antagonist of the classical D1A DAR. Lastly, we demonstrated that SKF83959 enhances [35S]guanosine 5′-O-(3-thiotriphosphate) binding to membrane Gαq and Gαi proteins, suggesting that PI stimulation is mediated by activation of these guanine nucleotide-binding regulatory proteins. Results indicate that SKF83959 is a selective agonist for the PI-linked D1-like DAR, providing a unique tool for investigating the functions of this brain D1 DAR subtype.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2003.01698.x
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  • 2
    Electronic Resource
    Electronic Resource
    Stimulated D1 dopamine receptors couple to multiple Gα proteins in different brain regions (2001)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 78 (2001), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Previous studies have revealed that activation of rat striatal D1 dopamine receptors stimulates both adenylyl cyclase and phospholipase C via Gs and Gq, respectively. The differential distribution of these systems in brain supports the existence of distinct receptor systems. The present communication extends the study by examining other brain regions: hippocampus, amygdala, and frontal cortex. In membrane preparations of these brain regions, selective stimulation of D1 dopamine receptors increases the hydrolysis of phosphatidylinositol/phosphatidylinositol 4,5-biphosphate. In these brain regions, D1 dopamine receptors couple differentially to multiple Gα protein subunits. Antisera against Gαq blocks dopamine-stimulated PIP2 hydrolysis in hippocampal and in striatal membranes. The binding of [35S]GTPγS or [α-32P]GTP to Gαi was enhanced in all brain regions. Dopamine also increased the binding of [35S]GTPγS or [α-32P]GTP to Gαq in these brain regions: hippocampus = amygdala 〉 frontal cortex. However, dopamine-stimulated binding of [35S]GTPγS to Gαs only in the frontal cortex and striatum. This differential coupling profile in the brain regions was not related to a differential regional distribution of the Gα proteins. Dopamine induced increases in GTPγS binding to Gαs and Gαq was blocked by the D1 antagonist SCH23390 but not by D2 receptor antagonist l-sulpiride, suggesting that D1 dopamine receptors couple to both Gαs and Gαq proteins. Co-immunoprecipitation of Gα proteins with receptor-binding sites indicate that in the frontal cortex, D1 dopamine-binding sites are associated with both Gαs and Gαq and, in hippocampus or amygdala, D1 dopamine receptors couple solely to Gαq. The results indicate that in addition to the D1/Gs/adenylyl cyclase system, brain D1-like dopamine receptor sites activate phospholipase C through Gαq protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2001.00470.x
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  • 3
    Electronic Resource
    Electronic Resource
    Characterization of the Phosphoinositide-Linked Dopamine Receptor in a Mouse Hippocampal-Neuroblastoma Hybrid Cell Line (1998)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 71 (1998), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Previous studies have established that dopamine (DA) can stimulate phosphoinositide (PI) metabolism in the CNS and in the periphery. The present study summarizes our attempt to find a cell line that expresses this dopaminergic system. We describe that the stable clonal HN33.11 cell line, established by fusion of mouse hippocampal cells with neuroblastoma cells (N18TG2) that originate from A/J mouse, natively expresses the D1 DA receptor system that couples to PI hydrolysis. In this cell line, 500 µM DA or SKF38393 produced 43 and 75% increases in inositol phosphate (IP) accumulations, respectively. In contrast, noradrenaline or 5-hydroxytryptamine did not affect IP accumulations. The formation of IP that was stimulated by DA or SKF38393 was selectively blocked by the D1 DA receptor antagonist SCH23390 with IC50 values of 13 and 16 µM. This response was not mediated by the D1A DA receptor and was cyclic AMP-independent, as HN33.11 cells did not express this receptor, and DA or SKF38393 was unable to stimulate the formation of cyclic AMP. In Ca2+-free/100 µM EGTA medium, basal IP level was reduced by 31.5%, but SKF38393-stimulated PI hydrolysis was not affected. SKF38393-stimulated IP accumulation was also not affected by pertussis toxin (PTX) treatment (200 ng/ml), suggesting that this dopaminergic response is mediated by PTX-insensitive G proteins. Co-immunoprecipitation studies indicated that in membranes of HN33.11 cells, D1-like binding sites are coupled to Gαq protein. Blockade of SKF38393-induced PI hydrolysis with antiserum against phospholipase C (PLC) isozymes, performed in permeabilized cells, as well as co-immunoprecipitation studies implicate PLCβ3 and PLCβ4 in this dopaminergically mediated PI hydrolysis cascade. The results indicate that HN33.11 cells express a D1-like DA receptor that couples to PLCβ3/4 via Gαq protein. These cells may therefore be a useful model system for investigating this receptor system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1998.71051935.x
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  • 4
    Electronic Resource
    Electronic Resource
    Dependence of excitotoxic neurodegeneration on mitochondrial aconitase inactivation (2001)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 78 (2001), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Using the inactivation of mitochondrial and cytosolic aconitases as markers of compartment-specific superoxide (O2−) production, we show that oxygen-glucose deprivation (OGD) or excitotoxin exposure produce a time-dependent inactivation of mitochondrial, but not cytosolic, aconitase in cortical cultures. To determine if mitochondrial O2− production was an important determinant in neuronal death resulting from OGD, metalloporphyrins with varying superoxide dismutase (SOD) activity were tested for their ability to protect against mitochondrial aconitase inactivation and cell death. OGD-induced mitochondrial aconitase inactivation and cell death was inhibited by manganese tetrakis (4-benzoic acid) porphyrin (MnTBAP), manganese tetrakis (N-ethylpyridinium-2-yl) porphyrin (MnTE-2-PyP) and NMDA receptor antagonists. By contrast, NMDA- or kainate (KA)-induced mitochondrial aconitase inactivation and cell death was inhibited by MnTBAP, but not MnTE-2-PyP. Moreover, both MnTBAP and MnTE-2-PyP penetrated mitochondrial fractions of cortical cells. These data suggest that mitochondrial aconitase inactivation closely correlates with subsequent neuronal death following excitotoxicity produced by OGD or NMDA/KA exposure. Assessment of biological rather biochemical antioxidant activities better predicted neuroprotection by metalloporphyrins. Moreover, antioxidants that protect oxidant-sensitive mitochondrial targets such as aconitase may be useful as therapies for disease states involving excitotoxicity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2001.00457.x
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  • 5
    Electronic Resource
    Electronic Resource
    Activation of NADPH oxidase and extracellular superoxide production in seizure-induced hippocampal damage (2005)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 92 (2005), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We sought to determine whether the extracellular compartment contributed to seizure-induced superoxide (O2.−) production and to determine the role of the NADPH oxidase complex as a source of this O2.− production. The translocation of NADPH oxidase subunits (p47phox, p67phox and rac1) was assessed by immunoblot analysis and NADPH-driven O2.− production was measured using 2-(4-hydroxybenzyl)-6-(4-hydroxyphenyl)-8-benzyl-3,7-dihydroimidazo [1,2-α] pyrazin-3-one-enhanced chemiluminescence. Kainate-induced status epilepticus resulted in a time-dependent translocation of NADPH oxidase subunits (p47phox, p67phox and rac-1) from hippocampal cytosol to membrane fractions. Hippocampal membrane fractions from kainate-injected rats showed increased NADPH-driven and diphenylene iodonium-sensitive O2.− production in comparison to vehicle-treated rats. The time-course of kainate-induced NADPH oxidase activation coincided with microglial activation in the rat hippocampus. Finally, kainate-induced neuronal damage and membrane oxygen consumption were inhibited in mice overexpressing extracellular superoxide dismutase. These results suggest that seizure activity activates the membrane NADPH oxidase complex resulting in increased formation of O2.−.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.2004.02838.x
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