Astrocyte [Ca ²⁺]_i transients evoked by activation of P2Y₁ and PAR-1 receptors. A, Representative images of the stratum radiatum region of the hippocampus with astrocytes showing increases in [Ca ²⁺]_i during activation of PAR-1 receptors with TFLLR peptide (30 µm). Arrowheads point to astrocytes showing intracellular calcium transients. B, Exemplar traces PAR-1- and P2Y₁-evoked [Ca ²⁺]_i transients. C, D, Pooled data for experiments such as those in A. The gray lines are individual cells, and the solid lines are the averages from all cells. Activation of both P2Y₁ and PAR-1 receptors evoked increases in astrocyte [Ca ²⁺]_i levels. E, The average normalized traces for [Ca ²⁺]_i transients evoked by P2Y₁ and PAR-1 receptor activation; note that there was a latency for the PAR-1-mediated responses in relation to those mediated by P2Y₁ receptors, and their duration was longer.

Dialysis of astrocytes with BAPTA via the patch pipette abolishes the PAR-1 agonist-evoked SICs in pyramidal neurons. A, Diagram of the hippocampus; the green box shows the stratum radiatum area that we focused on for astrocyte dialysis and recording. B, A flattened confocal stack shows numerous astrocytes that were dialyzed with Alexa Fluor 488 after patching a single astrocyte (the patch pipette is seen entering from the right). C, As in B but for dialysis with Alexa Fluor 488 and 10 mm BAPTA; note that many astrocytes were dialyzed. D, GFP-positive astrocytes from the stratum radiatum region of brain slices harvested from GFAP-GFP mice. Note that many astrocytes expressed GFP. E, A summary bar graph of the numbers of astrocytes that were dialyzed with Alexa Fluor 488 and BAPTA, and the number of astrocytes counted from GFAP-GFP mice. F, Top, An IR-DIC image of the surface of a hippocampal slice for the region shown in A. Astrocytes within ~150 –200 µm of the pyramidal layer were patched and dialyzed with Alexa Fluor 488 and BAPTA. Bottom, A fluorescence image of the same slice. Note that astrocytes were dialyzed even on the surface of the slice. The total number of astrocytes dialyzed within 90 µm depth is presented in E. G, Top, A representative trace of PAR-1 agonist-evoked SICs arriving onto pyramidal neurons in a slice without BAPTA dialysis into astrocytes. Bottom, The same experiment, but in this case for slices in which astrocytes near the pyramidal neuron had been dialyzed with BAPTA. Note that in this case, there were no SICs. The asterisks indicate SICs. Average data are presented in the text. DG, Dentate gyrus; SP, stratum pyramidale; wt, wild type.

Effect of astrocyte [Ca ²⁺]_i excitation on glutamatergic SICs onto pyramidal neurons. A, Representative (top) and average (bottom) traces for SICs and EPSCs recorded from a pyramidal neuron (average data are presented in the text). B, Activation of PAR-1 receptors led to the appearance of SICs. C, The spontaneous SICs were reduced or abolished with APV and ifenprodil, and in slices pretreated with FA and BAPTA-AM. D, PAR-1 agonist-evoked SICs were abolished in the presence of ifenprodil or in slices pretreated with FA or BAPTA-AM.