Periodic 17β-Estradiol Pretreatment Protects Rat Brain from Cerebral Ischemic Damage via Estrogen Receptor-β

Although chronic 17 beta-estradiol (E-2) has been shown to be a cognition-preserving and neuroprotective agent in animal brain injury models, concern regarding its safety was raised by the failed translation of this phenomenon to the clinic. Previously, we demonstrated that a single bolus of E-2 48 hr prior to ischemia protected the hippocampus from damage in ovariectomized rats via phosphorylation of cyclic-AMP response element binding protein, which requires activation of estrogen receptor subtype beta (ER-beta). The current study tests the hypothesis that long-term periodic E-2-treatment improves cognition and reduces post-ischemic hippocampal injury by means of ER-beta activation. Ovariectomized rats were given ten injections of E-2 at 48 hr intervals for 21 days. Hippocampal-dependent learning, memory and ischemic neuronal loss were monitored. Results demonstrated that periodic E-2 treatments improved spatial learning, memory and ischemic neuronal survival in ovariectomized rats. Additionally, periodic ER-beta agonist treatments every 48 hr improved post-ischemic cognition. Silencing of hippocampal ER-beta attenuated E-2-mediated ischemic protection suggesting that ER-beta plays a key role in mediating the beneficial effects of periodic E-2 treatments. This study emphasizes the need to investigate a periodic estrogen replacement regimen to reduce cognitive decline and cerebral ischemia incidents/impact in post-menopausal women.