Gender Effects On Neuroprotection And Cognitive Rehabilitation Of Estrogen After Cerebral Ischemia

BackgroundIschemic cerebrovascular disease (ICVD) with high incidence and high mortality and high morbidity, is a serious hazard to human health. Transient cerebral ischemia induces selective, delayed neuronal death in the hippocampal CA1 and delayed cognitive deficits. Cognitive impairment, including deficiencies in learning and memory performance, is common after ischemic stroke and burdens to the society and families. Postmenopausal women are in an estrogen-deprived state and are at risk for stroke and postmenopausal estrogen therapy reduces the risk. Investigations to date have demonstrated that estrogens are neuroprotective in animal models of ischemia. Estrogen is a steroid hormone secreted by the ovaries and adrenal glands. Neuroprotective mechanisms of estrogen include the classic receptor dependent mechanism and receptor-independent mechanism. In central nervous system, estrogen interacts with two different nuclear receptors, ER-αand ER-β, both of which act in concert with other transcription factors to regulate gene expression. Researchers have concluded that ER-αis a necessary mediator of estrogen neuroprotection in female rats. In males, the injury-induced regulation of estrogen receptors and the mechanisms of estradiol action are still largely unknown. Studies using ERβagonists in mice demonstrated that neuroprotection following global ischemia is mediated by ERβ, but other researchers hold the opposite views. The regulation of ERβin the cortex in both sexes following injury is critical to our comprehension of estrogen-mediated neuroprotective mechanisms. Estrogen therapy improves cognitive function, including memory and learning processes in a global ischemia model. However, in our clinical practice, the incidence of focal cerebral ischemia is larger than global ischemia. Because of the differences between ischemic modes, the paths of neuronal apoptosis, neurological damage and cognitive function are far away in focal and global ischemia. However, investigations to date have demonstrated that the underlying etiology, causes and burden of stroke may be different between females and males, the effects of gender and hormones on cognitive functions in stroke are not well documented.ObjectiveIn our present study, to test the hypothesis that acute estradiol treatment would differentially accelerate cognitive recovery after focal brain ischemia and that the recovery would be related to gender dependent regulation of estrogen receptors in male and female rats, we have extensively assessed the effects of gender and acute estrogen treatment on spatial learning and memory, and then evaluated the expression of estrogen receptors after focal cerebral ischemia.Methods1. Cerebral ischemia model Using the modified middle cerebral artery occlusion (MCAO) model, animals were treated with transient MCAO (tMCAO) for 1.5 hours .2. Determination of Infarct Volume The volume of infarct was evaluated by 2,3,5-triphenyltetrazolium chloride (TTC).3. Neurological function assessment Zeal Longa rating method was employed to assess the neurological functions.4. Immunohistochemistry (IHC) We use IHC to detect the expression of estrogen receptor(ER) alpha and beta protein.5. RT-PCR To evaluate the mRNA expression of ER alpha and beta, RT-PCR was applied.6. Evaluation of cognitive function Two weeks after tMCAO, we utilized Morris Water Maze to assess spatial learning and memory.7. Statistics Statistical analysis was performed using SPSS Statistics 17.0 software (SPSS Inc, Chicago, USA). All data are presented as means±SEM. Two-way analysis of variance, one-way ANOVA and post-hoc comparisons were made where appropriate. All differences were considered significant at p< 0.05.ResultsOur data suggest that acute estradiol treatment reduced infarct size after tMCAO in adult SD rats. Ischemia increases ERαprotein and mRNA expression in the cortex in OVX female while acute estradiol treatment increases ERβprotein and mRNA in male rats. Our data also indicate that acute estradiol treatment reduced spatial memory deficits in male estradiol-treated rats. Data in present study suggest that acute estradiol treatment when administered after the onset of focal ischemia did not prevent deficits in spatial memory in female OVX rats. These results indicated that acute estradiol treatment results in a gender difference in cognitive recovery following tMCAO.