Fig. 2.

Stimulus-induced γ frequency oscillations can precede seizure-like events under epileptogenic conditions. Field potential (fp) and membrane potential (ic) recordings from CA1 and CA3 strata pyramidale.A, Adult hippocampal slices reveal typical oscillation induced by paired stimuli (insets) in CA1, but not in CA3. A1, The oscillation is associated with a prolonged depolarization of a CA1 neuron, and, in this example, with prolonged afterdischarges or a seizure-like event in CA1, but not CA3. The region in the dashed box is expanded below, into thelarge dashed box, to show the early γ component and the onset of the epileptiform afterdischarges (*; action potentials are truncated on the ic trace). A2, CA3 neurons only show short depolarizations during the CA1 γ oscillation. In this experiment, no ictal activity followed the oscillation, although interictal bursts were present (calibrations same asA1). B, Juvenile hippocampal slices reveal typical oscillation (insets) in CA1, which is again not apparent in CA3. B1, The oscillation (from a P21 rat) is associated with a prolonged depolarization of a CA1 neuron and with prolonged afterdischarges or a seizure-like event in CA1, but not CA3. B2, CA3 neurons only show short depolarizations during γ oscillation in CA1, in spite of their involvement in the later ictal activity (from a P16 rat; calibrations same asB1). Note that ictal activity followed the oscillation in both CA1 and CA3 only in juvenile slices.