Figure 2. Gradual increase of the glutamatergic drive and increase of the GABAergic drive in CA1 pyramidal cell somata during epileptogenesis.

A, photomicrograph of a biocytin-filled pyramidal cell during the late latent period. The arrow indicates the recording site. Scale bar represents 5 μm. B, traces at the top are recordings of spontaneous EPSCs in somata in sham, late latent (cell shown in A) and epileptic animals. Note the transient decrease in EPSC frequency during the early latent period and the increase in frequency during the chronic period, as shown in the histogram on the bottom right (*P < 0.002, Student's unpaired t test). The graphs are cumulative probability plots of amplitude, 10–90% rise time, decay time constant and charge transfer of EPSCs in all recorded cells. Although the EPSC charge transfer is decreased during the early latent period owing to a decrease in amplitude, it is increased during the late latent period as a result of the increase in rise time and decay time constant. The charge transfer is further increased during the chronic period owing to an increase in amplitude and rise time. Normalized average EPSCs are displayed in the inset. C, traces at the top are recordings of spontaneous IPSCs in somata in sham, late latent (cell shown in A) and epileptic animals. Note the transient decrease in frequency during the early and late latent periods as shown in the histogram on the bottom right (*P < 0.05, Student's unpaired t test). The graphs are cumulative probability plots of amplitude, 10–90% rise time, decay time constant and charge transfer of IPSCs in all recorded cells. There was no modification in the distribution in amplitudes, whereas rise times and decay time constants, hence IPSC charge transfers, were increased during the early and late latent periods. Decay time constants and IPSC charge transfers reversed to near control levels during the chronic phase. Normalized average IPSCs are displayed in the inset.