Estrogen Modulation of Bursting Activity in GnRH Neurons

描述(由申请人提供)：本项目的总体目标是确定17β-雌二醇(E2)调节GnRH神经元兴奋性的机制。GnRH神经元对该物种的生存至关重要，而E2和神经递质对这些神经元的神经分泌特性都是至关重要的。然而，关于GnRH神经元被调控的细胞机制，人们只有有限的了解。近年来，绿色荧光蛋白(EGFP)标记的GnRH神经元转基因小鼠的发展极大地促进了对这些重要神经元的研究。最近的证据表明，E2通过ERbeta直接作用于GnRH神经元，也间接通过ERpha作用于GABA神经元，从而影响GnRH的产生和/或释放。此外，雌二醇改变了神经递质的效力，这些递质可能直接或间接影响促性腺激素释放激素神经元。尽管人们越来越重视这一点，但E2对GnRH神经元的调控尚不完全清楚。为了进一步探索支配GnRH兴奋性的GnRH神经元的独特电学特性以及E2如何调节这些特性，我们将基于GnRH神经元爆发放电的模型，重点研究选择性离子通道和受体。我们的工作假设是，E2通过膜信号事件强烈地调节突触输入和离子通道功能，并在较长时间内改变GnRH神经元中特定受体和离子通道的表达。这些变化将增强或抑制GnRH神经元的活动和GnRH的释放，这取决于女性的类固醇里程，这最终调节生育。 我们的具体目标集中在促黄体生成素(GnRH)分泌正反馈过程中调节GnRH神经元的关键问题：(1)检测ATP敏感性钾通道亚单位的mRNA表达，并确定E2是否改变这种表达。(2)检测E_2对K-ATP通道功能的急性影响，并探讨其细胞机制(S)。(3)探讨雌二醇是否能增加α1肾上腺素能受体的基因表达和蛋白表达。(4)测定E_2对小电导钙激活钾(SK)电流的α1-肾上腺素能抑制的影响。(5)探讨E_2是否可增加钙T通道亚基的基因表达，增强T通道的活性，从而增强爆发式放电。这些研究将为雌激素如何改变下丘脑GnRH神经元的内在电导以及雌激素如何改变突触输入从而促进GnRH神经元不同的放电模式提供新的重要信息，而GnRH神经元是生殖能力的关键。

DESCRIPTION (provided by applicant): The overall objectives of this project are to ascertain the mechanisms by which 17 beta-estradiol (E2) regulates GnRH neuronal excitability. GnRH neurons are crucial for the survival of the species, and both E2 and neurotransmitters are critical for the neurosecretory properties of these neurons. However, only limited knowledge is available on the cellular mechanisms by which GnRH neurons are regulated. The recent development of transgenic mice with green fluorescent protein (EGFP)-tagged GnRH neurons has greatly facilitated studies of these important neurons. Recent evidence suggests that E2 through ERbeta acts directly on GnRH neurons, as well as indirectly through ERalpha on GABA neurons to affect GnRH production and/or release. In addition, E2 alters the potency of neurotransmitters that may directly or indirectly affect GnRH neurons. Despite this growing appreciation, E2 regulation of GnRH neurons is incompletely understood. To further explore the distinct electrical properties of GnRH neurons that govern GnRH excitability and how E2 modulates these properties, we will focus on selective ion channels and receptors based on a model for burst firing in GnRH neurons. Our working hypothesis is that E2 modulates synaptic input and ion channel function acutely through membrane signaling events and over a longer time period alters the expression of specific receptors and ion channels in GnRH neurons. These changes will enhance or inhibit GnRH neuronal activity and GnRH release depending on the steroid mileu of the female, which ultimately regulates fertility. Our Specific Aims focus on key issues regulating GnRH neurons during positive feedback of LH (GnRH) secretion: (1) To measure the mRNA expression of ATP-sensitive potassium channel subunits, and determine whether E2 alters this expression. (2) To measure the acute effects of E2 on K-ATP channel function, and determine the cellular mechanism(s). (3) To ascertain whether E2 increases alpha1-adrenergic receptor mRNA expression and protein. (4) To measure the effects of E2 on the alpha1-adrenergic inhibition of a small conductance calcium-activated K+ (SK) current that underlies the medium afterhyperpolarization. (5) To ascertain whether E2 increases the mRNA expression of calcium T-channel subunits, and increases T-channel activity leading to enhanced burst firing. These studies will provide new and important information on how estrogen alters intrinsic conductances of hypothalamic GnRH neurons and how estrogen in general modifies synaptic input and thereby facilitates distinct firing patterns in GnRH neurons, which is critical for reproductive competence.