Figure 2. I_h block abolishes the hyperpolarizing phase of the EPSP–IPSP sequence.

(a) EPSP–IPSP sequences were evoked in CA1 pyramidal cells by Schaffer collateral stimulation as in Figure 1. Consecutive traces from a representative experiment showing a shift in V_R following ZD-7228 application, associated abolition of the GABA_A receptor-mediated hyperpolarizing component of the EPSP–IPSP sequence (GABA_B receptors are blocked with 5 μM CGP52432) and the overall contribution of inhibition revealed by subsequent application of picrotoxin (PTX). (b) Summary of ZD-7288 effect on EPSP–IPSP characteristics with (direct current (DC)) and without constant current injection to compensate for ZD-7288-induced shift in V_R (n=4 cells; shaded columns: ZD-7288, open columns: ZD-7288+DC). Overlapped averaged traces are shown on the left (prepulse baseline is normalized). (c) Effect of application of ZD-7288 on the amplitude and duration of pharmacologically isolated EPSPs, while maintaining V_R with current injection (n=7; recordings were made in the presence of 5 μM CGP52432 and 100 μM picrotoxin); this effect is similar to the effect of ZD-7288 on the EPSP–IPSP sequence+DC (b). Bar charts represent percentage change of control values; error bars represent s.e.m.; *P<0.05, **P<0.01, ***P<0.001.