Fig. 3.

Graphical representation of the experiment shown in Figure 2. A, This image is the black and white equivalent of image b in Figure 2. The relative fluorescence of the indicated regions (1–5) of the astrocytes was monitored. B, This graph illustrates the relative changes in calcium for the regions labeled in A. The lettersa–d correspond to imagesa–d of Figure 2. The position of the letters indicates where in the time sequence the image was taken. Theopen bar at the bottom indicates when the stimulation (200 μA, 50 Hz, 2 sec) was applied to the Schaffer collaterals. The traces in this graph and all subsequent graphs were arbitrarily shifted along the ordinate axis for clarity. C, This field potential was induced by a single test pulse of 200 μA just before the experiment. The presynaptic and postsynaptic portions of the field potential are indicated by the open arrow and the filled arrow, respectively.