We have found that gonadal steroid hormones affect information processing differently in male and female hippocampus. Experiments are proposed which are designed to examine this effect in detail. The in vitro hippocampal slice system will be used as the neurophysiological model for all studies. Activity in monosynaptic circuits of the hippocampus (Schaffer collateral to CA1 pyramid) and dentate gyrus (perforent path fibers to granule cell) will be monitored. The proposed experiments will address the issues of whether the observed effects are attributable to "organizing" or "activating" functions of sex hormones, whether classical receptor binding of steroids is involved and whether the effects are specific to sex steroids.