Abstract: Objective To investigate the effects of estrogen on extracellular signal-regulated kinase-1/2(ERK1/2)phosphorylation levels in hippocampal CA4 region of ovariectomized rats.MethodsExperimental female Wistar rats were randomly divided into three groups:intact(INT)group,ovariectomized(OVX)group,and OVX+estrogen (1 mg/kg,weekly)group.Radioimmunoassay(RIA)was used to measure the estrogen content in plasma,and the levels of ERK1/2 phosphorylation were measured with immunohistochemistry.ResultsCompared with the control animals,the plasma estrogen level was significantly lower in OVX group(P<0.001).However,the plasma estrogen level was higher in the OVX+estrogen group than that of the OVX group(P<0.001).Immunohistochemical staining showed that the phospho-ERK1/2(p-ERK1/2)substances were present in the nucleus and cytosol of neurons.Compared with the control group,immunostaining positive cells markedly decreased in OVX group,with light nucleus and cytosol staining in the hippocampal CA4 region(P<0.001).The phospho-ERK1/2 positive neurons increased more obviously in OVX+estrogen group than in the OVX group(P<0.001).ConclusionEstrogen can increase ERK1/2 phosphorylation levels in hippocampi of aging female rats,which suggests that the ERK signal transduction pathway may be regulated by estrogen during the process of aging.

Key words: estrogen, ovariectomy, hippocampus, extracellular signal-regulated kinase, rats