Figure 4.
Changes in the glutamatergic and GABAergic postsynaptic currents associated with the spontaneous rhythmic field potentials of CA3 non-FS interneurons during the preictal period. Low-Mg2+/high-K+-induced SLEs are recorded simultaneously from a voltage-clamped CA3 non-FS interneuron (top traces) and the CA3 stratum oriens field (bottom traces). The electrodes are <100 μm apart. Ai–Bii, The glutamatergic and GABAergic currents were recorded by clamping the neuron at −60 mV (Ai, Aii) and 0 mV (Bi, Bii) respectively. Aii, Bii, The preictal activity seen in Ai and Bi is shown at a faster time base, and the preictal bursts were numbered for quantitative analysis. The high-frequency ictal onsets are indicated by the open arrows. The charge transfers were measured for eight preictal bursts synchronized with the recurrent epileptiform field events (p-8 to p-1) and were normalized against the burst at p-9. C, D, Normalized charge transfers associated with different preictal discharges were plotted for both glutamatergic postsynaptic currents (C) and GABAergic postsynaptic currents (D; n = 15). Note that the EPSCs gradually but markedly increased (to almost 10 times control) from p-4 to p-1 and became the dominant currents during the ictus. On the other hand, IPSCs gradually decreased during the late preictal period. However, the decrease is insignificant, except for at p-1, where inward current was observed in this example. *p < 0.05 (one-way ANOVA).