REGULATION OF DENDRITIC SPINE DENSITY IN CULTURED RAT HIPPOCAMPAL-NEURONS BY STEROID-HORMONES

The effects of gonadal steroid hormones on dendritic spines were studi ed in hippocampal neurons that were dissociated and grown in culture f or 2-3 weeks, Exposure to estradiol caused up to a twofold increase in dendritic spine density in these neurons. The effect of estradiol was stereospecific and blocked by the steroid antagonist tamoxifen. The e stradiol-induced rise in spine density was blocked by the NMDA antagon ist APV, but not by the AMPA/KA antagonist DNQX. The estradiol-induced rise in spine density was blocked by the serine/threonine kinase inhi bitor H7, but not by the tyrosine kinase inhibitor genestein, and was partially mimicked by PMA, an activator of protein kinase C. Estradiol also caused an increase in the fluorescence intensity of synaptophysi n-immunoreactive terminals, corresponding to presynaptic boutons. Fina lly, estradiol caused a rise in [Ca](i) reactivity of the cultured neu rons to topical application of glutamate, These studies are the first to examine receptor and second messenger regulation of dendritic spine s, and they illustrate the viability of cultured neurons as a powerful test system to address issues related to the regulation of dendritic spine maturation.