Figure 7.

Astrocyte-evoked SICs and epileptiform activity are two distinct electrophysiological events. A–C, Simultaneous recording from a pyramidal cell in the CA1 region (middle trace in each panel) and two distal extracellular electrodes placed in the CA3b and CA3c regions (top and bottom traces in each panel, respectively). When the slice is challenged with 0 Mg²⁺ and picrotoxin (A), synchronous ictal-like events are recorded from all of the electrodes. In contrast, locally generated SICs (asterisk) are recorded only by the whole-cell patch electrode and not by the extracellular electrode. For an example of ictal-like event and SIC displayed at an expanded timescale, see inset. In the same experiment shown in A, application of d-AP-5 (B; 50 μm) blocks SIC but not epileptiform activity. Note that, in this experiment, application of d-AP-5 results in a switch of the duration of epileptiform activity from ictal- to interictal-like, as described previously (see legend of Fig. 6). Subsequent washout of d-AP-5 results in the recovery of the SIC activity (C). D, Average SIC (left) and epileptiform event (right) frequency under the different experimental conditions shown in A–C (n = 4 experiments).