TY - JOUR T1 - Stimulation-Evoked Ca<sup>2+</sup> Signals in Astrocytic Processes at Hippocampal CA3–CA1 Synapses of Adult Mice Are Modulated by Glutamate and ATP JF - The Journal of Neuroscience JO - J. Neurosci. SP - 3016 LP - 3021 DO - 10.1523/JNEUROSCI.3319-14.2015 VL - 35 IS - 7 AU - Wannan Tang AU - Karolina Szokol AU - Vidar Jensen AU - Rune Enger AU - Chintan A. Trivedi AU - Øivind Hvalby AU - P. Johannes Helm AU - Loren L. Looger AU - Rolf Sprengel AU - Erlend A. Nagelhus Y1 - 2015/02/18 UR - http://www.jneurosci.org/content/35/7/3016.abstract N2 - To date, it has been difficult to reveal physiological Ca2+ events occurring within the fine astrocytic processes of mature animals. The objective of the study was to explore whether neuronal activity evokes astrocytic Ca2+ signals at glutamatergic synapses of adult mice. We stimulated the Schaffer collateral/commissural fibers in acute hippocampal slices from adult mice transduced with the genetically encoded Ca2+ indicator GCaMP5E driven by the glial fibrillary acidic protein promoter. Two-photon imaging revealed global stimulation-evoked astrocytic Ca2+ signals with distinct latencies, rise rates, and amplitudes in fine processes and somata. Specifically, the Ca2+ signals in the processes were faster and of higher amplitude than those in the somata. A combination of P2 purinergic and group I/II metabotropic glutamate receptor (mGluR) antagonists reduced the amplitude of the Ca2+ transients by 30–40% in both astrocytic compartments. Blockage of the mGluRs alone only modestly reduced the magnitude of the stimulation-evoked Ca2+ signals in processes and failed to affect the somatic Ca2+ response. Local application of group I or I/II mGluR agonists or adenosine triphosphate (ATP) elicited global astrocytic Ca2+ signals that mimicked the stimulation-evoked astrocytic Ca2+ responses. We conclude that stimulation-evoked Ca2+ signals in astrocytic processes at CA3–CA1 synapses of adult mice (1) differ from those in astrocytic somata and (2) are modulated by glutamate and ATP. ER -