Figure 2.

Developmental expression of the GABAergic [K⁺]_o transient and the consequent tonic depolarization. a, Intracellular recordings from CA1 pyramidal cells before and after the expression of intracellular carbonic anhydrase. At P11 (V_m = –69 mV) the pharmacologically isolated GABA_A-mediated depolarizing response is small and EZA (100 μm) has little effect on it. The HFS-induced GABAergic depolarization is attenuated by EZA only after intrapyramidal carbonic anhydrase is expressed (P17; V_m = –72 mV). Spikes are truncated. b, Simultaneous GABAergic [K⁺]_o and field potential recordings in CA1 stratum pyramidale. Both HFS-induced gamma oscillation and the [K⁺]_o transient show a marked sensitivity to EZA only after P12. The 10 mV calibration refers to the K⁺ electrode differential signal (and corresponds to a 1.5 mm increase in [K⁺] from 3 mm), and 2 mV refers to field potential. c, The effect of EZA on the amplitude of the HFS-induced [K⁺]_o transient plotted against postnatal age, Filled circles, Slices in an interface chamber; open circles, slices in a submersion chamber. d, Simultaneous recordings with field potential, K⁺- and TeMA⁺-sensitive microelectrodes in CA1 stratum pyramidale of a P34 slice. The 20 and 2 mV calibrations refer to the ion electrode differential signals and the field signal, respectively. All experiments were performed in the presence of NBQX, AP-5, and CGP-55845A.