Novel target sites for estrogen action in the dorsal hippocampus: An examination of synaptic proteins

Structural studies have shown that estrogens increase dendritic spine numbe r in the dorsal CA1 field of rat hippocampus using Golgi impregnation as we ll as the number of dorsal CA1 synapses visualized via electron microscopy. The present study was carried out to further these findings by examining c hanges in the levels of pre- and postsynaptic proteins using radioimmunocyt ochemistry (RICC). In this study, 2 days of estradiol-benzoate treatment pr oduced significant and comparable increases in synaptophysin, syntaxin, and spinophilin immunoreactivity (IR) in the CA1 region of the dorsal hippocam pus of ovariectomized female rats. For spinophilin, IR was also increased i n the hilar region of the dentate gyrus as well as CA3. In all cases, the n onsteroidal estrogen antagonist CI628, which has been previously shown to b lock spine formation, inhibited the effects of estrogen. However, these pro tein differences were not detected in whole hippocampus using Western blots . These findings add to a growing body of evidence that estrogens increase synapses in the CA1 region of hippocampus along with changes in previously unidentified sites. These results also suggest that RICC is a rapid and sen sitive method for examining molecular changes in synaptic profiles in anato mically distinct brain regions.