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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The cytokine interleukin (IL)-6 has recently been demonstrated to play a role in the pathology of Alzheimer's disease (AD). The mechanisms leading to increased IL-6 levels in brains of AD patients are still unknown. Because in experimental animals ischemia increases both the level of cytokines and the extracellular concentrations of adenosine in the brain, we hypothesized that these two phenomena may be functionally connected and that adenosine might increase IL-6 gene expression in the brain. Here we show that the mixed A1 and A2 agonist 5′-(N-ethylcarboxamido)adenosine (NECA) induces an increase in IL-6 mRNA levels and protein synthesis in the human astrocytoma cell line U373 MG. The A1-specific agonists R-phenylisopropyladenosine and cyclopentyladenosine are much less potent, and the A2a-specific agonist CGS-21680 shows only marginal effects. Increased levels of mRNA are already found within 30 min after NECA treatment. The A2a-selective antagonists 8-(3-chlorostyryl)caffeine and KF17837 [(E)-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-methylxanthine], which have also some antagonistic properties at A2b receptors, and the nonspecific adenosine antagonist 8-phenyltheophylline were equipotent at inhibiting the NECA-induced increase in IL-6 protein synthesis, whereas the specific A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine is much less potent. The results indicate that adenosine A2b receptors participate in the regulation of the IL-6 gene in astrocytoma cells.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Stimulation of astrocytes with the excitatory neurotransmitter glutamate leads to the formation of inositol 1,4,5-trisphosphate and the subsequent increase of intracellular calcium content. Astrocytes express both ionotropic receptors and metabotropic glutamate (mGlu) receptors, of which mGlu5 receptors are probably involved in glutamate-induced calcium signaling. The mGlu5 receptor occurs as two splice variants, mGlu5a and mGlu5b, but it was hitherto unknown which splice variant is responsible for the glutamate-induced effects in astrocytes. We report here that both mRNAs encoding mGlu5 receptor splice variants are expressed by cultured astrocytes. The expression of mGlu5a receptor mRNA is much stronger than that of mGlu5b receptor mRNA in these cells. In situ hybridization experiments reveal neuronal expression of mGlu5b receptor mRNA in adult rat forebrain but a strong neuronal expression of mGlu5a mRNA only in olfactory bulb. Signals for mGlu5a receptor mRNA in the rest of the brain were diffuse and weak but consistently above background. Activation of mGlu5 receptors in astrocytes yields increases in inositol phosphate production and transient calcium responses. It is surprising that the rank order of agonist potency [quisqualate 〉 (2S, 1′S,2′S)-2-(carboxycyclopropyl)glycine = trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid (1S, 3R-ACPD) 〉 glutamate] differs from that reported for recombinantly expressed mGlu5a receptors. The expression of mGlu5a receptor mRNA and the occurrence of 1S, 3R-ACPD-induced calcium signaling were found also in cultured microglia, indicating for the first time expression of mGlu5a receptors in these macrophage-like cells.
    Type of Medium: Electronic Resource
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