Fig. 6. In the presence of 4-AP, the astrocytic responses are attributable to stimulation of both metabotropic and ionotropic glutamate receptors. A, This graph illustrates the effect of MCPG (1 mm) and KY (3 mm) on the responses of three different hippocampal astrocytes in situ to Schaffer collateral stimulation (400 μA, 50 Hz, 2 sec; asterisks) in the presence of 4-AP (100 μm). The lettersa–c indicate when the field potentials inB were measured. B, The field potentials were measured before (a), during (b), and after (c) treatment with MCPG and KY. C, This graph demonstrates the effect of MCPG (1 mm) and TTX (1 μm) on the responses of three different hippocampal astrocytes in situ to Schaffer collateral stimulation (200 μA, 50 Hz, 2 sec; asterisks) in the presence of 4-AP (100 μm). The lettersa–c indicate when the field potentials inD were measured. D, The field potentials were recorded in the absence of 4-AP (a), in the presence of 4-AP (b), and in the presence of 4-AP and MCPG (c).E, This graph illustrates the effect of KY (3 mm) on the responses of three different hippocampal astrocytes in situ to Schaffer collateral stimulation (200 μA, 50 Hz, 2 sec; asterisks) in the presence of 4-AP (100 μm). The lettersa–d indicate when the field potentials inF were recorded. F, The field potentials were recorded in the absence of 4-AP (a), in the presence of 4-AP (b), in the presence of 4-AP and KY (c), and after washout of KY (d).