Figure 3.

Persistent epileptiform activity is associated with a reduction in GABAergic synaptic conductance. (A) Schematic of experimental setup showing whole-cell recordings being performed from CA1 pyramidal neurons in mouse organotypic brain slices where GAD2+ interneurons were transfected with ChR2-YFP and activated using a high-powered LED coupled to the objective. (B) Example GABA I-V plot from a whole-cell patch-clamp recording (low Cl⁻ internal, 10 mM) of a CA1 pyramidal cell in a mouse hippocampal organotypic slice. Inset: Raw current traces recorded at different holding potentials. GABA was evoked by optogenetic activation of ChR2 expressing GAD2+ interneurons with 100 ms blue light pulses. GABA conductance (g_GABA) was calculated from the slope of the GABA current I-V curve. The GABA current was calculated by subtracting the holding current (black line on inset) from the total current (blue line on inset) for each holding potential. (C) Example GABA I-V plot from the same cell as in B following cessation of persistent epileptiform activity generated by 30 min of 0 Mg²⁺ application. (D) Population data (n = 14) showing a significant decrease in g_GABA from baseline to after 30 min 0 Mg²⁺ (baseline: mean 23.6 ± SEM 4.1 nS versus 30 min of 0 Mg²⁺: mean 13.1 ± SEM 3.2 nS, P = 0.0001, paired t-test). ^****P ≤ 0.0001; error bars indicate mean ± SEM.