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  • Title: Selective stimulation of astrocyte calcium in situ does not affect neuronal excitatory synaptic activity.
    Author: Fiacco TA, Agulhon C, Taves SR, Petravicz J, Casper KB, Dong X, Chen J, McCarthy KD.
    Journal: Neuron; 2007 May 24; 54(4):611-26. PubMed ID: 17521573.
    Abstract:
    Astrocytes are considered the third component of the synapse, responding to neurotransmitter release from synaptic terminals and releasing gliotransmitters--including glutamate--in a Ca(2+)-dependent manner to affect neuronal synaptic activity. Many studies reporting astrocyte-driven neuronal activity have evoked astrocyte Ca(2+) increases by application of endogenous ligands that directly activate neuronal receptors, making astrocyte contribution to neuronal effect(s) difficult to determine. We have made transgenic mice that express a Gq-coupled receptor only in astrocytes to evoke astrocyte Ca(2+) increases using an agonist that does not bind endogenous receptors in brain. By recording from CA1 pyramidal cells in acute hippocampal slices from these mice, we demonstrate that widespread Ca(2+) elevations in 80%-90% of stratum radiatum astrocytes do not increase neuronal Ca(2+), produce neuronal slow inward currents, or affect excitatory synaptic activity. Our findings call into question the developing consensus that Ca(2+)-dependent glutamate release by astrocytes directly affects neuronal synaptic activity in situ.
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