GABA_B receptor activation enhanced GABA_A currents in DGGCs, but not CA1 pyramidal neurons or cortical layer 2/3 pyramidal neurons. A, GABA_A currents evoked by focal application of GABA (10 μm) before and during bath application of baclofen (20 μm) (left panel). Middle panel shows time course of current change during baclofen application for this cell. Horizontal bars indicate the period of drug application here and in subsequent figures. Right panel shows mean current amplitudes under control conditions (con) and in the presence of baclofen. B, GABA currents in the presence of the GABA_B antagonist CGP 55845 (10 μm) before and during baclofen application (left), time course of current change for this cell (middle), and mean current under control conditions (con) and in the presence of baclofen (right panel). CGP prevented baclofen effects on GABA_A currents. C, GABA currents before and after application of CGP alone (left), time course for this cell (middle), and mean current amplitude (right). D, Normalized currents (baclofen/control) for experiments on DGGCs, CA1 pyramidal cells, and layer 2/3 pyramidal cells. Error bars represent SEM; *p < 0.05, **p < 0.01, n.s., nonsignificant.