Steroid Hormones and Neuronal Survival-Molecular Biological Studies

在我们之前的研究中，我们发现雌激素能提高培养的大鼠海马神经元的存活率。在此基础上，我们进一步证实了0.5mg/kg β-雌二醇诱导大鼠大脑皮层和海马IGF-1 mRNA表达，并对雌激素诱导IGF-1 mRNA表达的信号转导途径进行了探索，取得了以下研究结果：1.雌激素可引起培养的大鼠海马神经元胞内钙离子浓度的短暂增加。硝苯地平可抑制这种增加.一般注射0.5mg/kg β-雌二醇诱导大鼠大脑皮层和海马c-fos mRNA表达在注射后30 min达到最大值.皮下注射0.5mg/kg β-雌二醇可增强海马和大脑皮层AP-1 DNA结合活性，120 min达最大值.皮下注射 ...更多信息 0.5mg/kg β-雌二醇可增加大脑皮层和海马CREB（cyclicamplespectionelementbindingprotein）DNA结合活性。在注射后45 min开始增加，并且在海马中结合持续增加直至120 min。在大脑皮层，CREB DNA结合活性的增加是短暂的. RNase保护实验表明，预先注射硝苯地平可阻断雌激素诱导的IGF-1 mRNA表达，但雌激素核受体部分拮抗剂三苯氧胺不抑制IGF-1 mRNA表达.近年来，有人提出，雌激素不仅在细胞核内，而且在细胞膜上也有特异性结合位点，它们与G蛋白结合，与环状AMP.in有关。我们的实验表明，在hippocarnpus中，雌激素引起雌激素受体α的上调，而这种上调被尼古丁抑制。这些现象是由于新发现的细胞膜雌激素结合位点、经典的核雌激素受体和烟碱受体之间的复杂的相互作用所致，因此，雌激素诱导的cAMP依赖性的神经元内Ca ~（2+）浓度的增加依次引起CREB DNA结合活性的增加、c-fos mRNA表达的诱导和AP-1 DNA结合活性的增加，最终诱导IGF-1 mRNA的表达。少

In our foregoing studies, we found that estrogen increased the survival rate of cultured rat hippocampal neurons. Then, we confirmed that a general injection of 0.5mg/kg beta-estradiol induced IGF-1 mRNA expression in the rat cerebral cortex as well as hippocampus.Motivated by these facts, we have been trying to pursuit the signal transduction passway through which estrogen induces IGF-1 mRNA expression, and have so far obtained the following results.1. Estrogen caused a transient increase of intracellular Ca ion concentration in some population of cultured rat hippocampal neurons. This increase was inhibited by nifedipine.2. A general injection of 0.5mg/kg beta-estradiol Induced c-fos mRNA expression reaching the maximum at 3OmIn after the injection in the rat cerebral cortex and hippocampus.3. A subcutaneous injection of 0.5mg/kg beta-estradiol potentiated the AP-1 DNA binding activities in both hippocampus and cerebral cortex reaching the maximum at 120min.4. A subcutaneous injectio … More n of 0.5mg/kg beta-estradiol increased the CREB (cyclic AMP response element binding protein) DNA binding activities in both cerebral cortex and hippocampus. The increase started at 45mm after the injection and the binding was continuously incremental up to 120min in the hippocampus. In the cerebral cortex, the increase of the CREB DNA binding activities was transient.5. When observed by RNase protection assay in the rat hippocarnpus, estrogen-induced IGF-1 mRNA expression was blocked by a previous injection of nifedipine, but not inhibited by tamoxifen, a nuclear estrogen receptor partial antagonist.6. Recently, it is advocated that there are estrogen specific binding sites not only in the nucleus but also on the cell membrane in which they are conjugated with G protein in relation with cyclic AMP.in our experiments, it was shown that in the hlppocarnpus, estrogen caused an upregulation of estrogen receptor alpha which was inhibited by nicotine . These phenomena were due to the complicated crosstalk among the newly-discovered membranous estrogen binding site, classical nuclear estrogen receptor and nicotinic receptor.Summarizing these results, it was concluded that estrogen-induced cyclic AMP-dependant intraneuronal Ca ion concentration caused increase of CREB DNA binding activity, induction of c-fos mRNA expression and then increase of AP-1 DNA binding activIties in succession, and finally brought about induction of IGF-1 mRNA expression. Less