Figure 3.

The GABA_A antagonist BMI unmasks hyperexcitability in p35-/- slices. A, Under controlconditions, stimulation of the perforant path (0.4 mA) elicits similar evoked responses in wild-type and knock-out animals. B, The addition of BMI increases the amplitude of the fEPSP and induces population spiking (black arrow) in the wild-type slices. An expansion of the early part of the response is shown beneath the slow time sweep; the bicuculline condition is superimposed over the control (gray) trace. In knock-out slices, the initial evoked response is similar to that seen under control conditions (only a small increase in the fEPSP amplitude); however, there is also a long-latency, long-duration, high-amplitude event (gray shading). Calibration: 0.5 mV (vertical), 25 msec (horizontal). C, Field potential amplitude under bicuculline conditions, measured at 150 msec after the stimulus, shows the consistent occurrence of the late discharge in p35-/- slices but not in wild-type slices.