Estrogen, progestogen and tamoxifen increase synaptic density of the hippocampus of ovariectomized rats

The effects of gonadal steroids or tamoxifen over the synaptic density of t he CA1 region of the hippocampus was investigated in ovariectomized (OVX) r ats. Chronic oral administration of conjugated equine estrogen, conjugated equine medroxyprogesterone, a combination of both or tamoxifen was performe d in ovariectomized (OVX) rats over a period of 60 days. Synaptic density o f the stratum radiatum of the CA1 region was evaluated by means of electron microscopy. Significant increases in the range of 34-49% were found for tr eated animals as compared to OVX controls not subject to hormonal replaceme nt. Our results confirm previously reported effects of estradiol over synap tic density in this region and reports for the first time an effect of medr oxyprogesterone (alone or in combination with estrogen) and tamoxifen. Our findings support the notion that hormonal replacement therapy and tamoxifen might have beneficial effects for cognitive function. (C) 2000 Published b y Elsevier Science Ireland Ltd.