Corticosterone can affect electrical properties of CA1 pyramidal neurons via binding to two corticoid receptor types, the mineralocorticoid (MR) and glucocorticoid receptor (GR). Previously we have shown that MR-activation leads to attenuation of serotonin (5-HT)-induced membrane hyperpolarization, while GR-activation induces an increase in the amplitude of the afterhyperpolarization (AHP) following a short current pulse. In this study we show that the MR- and GR-mediated changes of the membrane properties are prevented in the presence of the protein synthesis inhibitor cycloheximide, thus suggesting a genomic action of the steroids.