Changes in seizure frequency over the course of the menstrual cycle (i.e.,
catamenial epilepsy) have long been documented. Ovarian steroid hormones ha
ve a number of important short- and long-term effects on the brain that may
contribute to this phenomenon. In particular, estrogen induces structural
and functional changes in hippocampal neurons which may contribute signific
antly to increasing seizure susceptibility. This article reviews the mechan
isms of action of steroid hormones on the basis of findings in animal model
s, with particular emphasis on the effects of estrogen on the hippocampus.