17Beta-estradiol regulation of T-type calcium channels in gonadotropin-releasing hormone neurons.
17Beta-estradiol regulation of T-type calcium channels in gonadotropin-releasing hormone neurons.
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DOI：
10.1523/jneurosci.2962-09.2009
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发表时间：
2009-08-26
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通讯作者：
Rønnekleiv OK
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作者：
Zhang C;Bosch MA;Rick EA;Kelly MJ;Rønnekleiv OK
T型钙通道负责产生低阈值尖峰，促进神经元的爆发式放电和神经递质释放。促性腺激素释放激素神经元表现为爆发式放电，但其潜在的电导尚不清楚。在此之前，我们已经发现17-雌二醇(17β-estadiol，E_2)能增加下丘脑弓状核神经元的T型通道表达和兴奋性。因此，我们使用去卵巢的油或E2处理的EGFP-GnRH小鼠来探讨GnRH神经元中T-型通道的表达和E2的调节。基于单细胞逆转录聚合酶链式反应和实时定量聚合酶链式反应对T型通道α1亚基的定量，我们发现这三个亚基都在有≥3.3Gav3.2和Gt；Cav3.1的神经元中表达。早晨，随着E_2水平的升高，上述三个亚基的mRNA表达水平也随之升高。下午，CaV3.3mRNA的表达持续升高，而Cav3.1和Cav3.2的表达下降。膜雌激素受体激动剂STX可增加GnRH神经元CaV3.3的表达，但不能增加Cav3.2的表达。GnRH神经元全细胞膜片记录显示，在两个时间点，E2处理均显著增加T型电流密度，并增加下午的反弹兴奋。虽然E2调节GnRH神经元中所有三个亚单位的mRNA表达，但表达增加加上T型电流失活动力学较慢，表明CaV3.3可能是与GnRH/LH峰相关的爆发活动最重要的因素。雌激素诱导的mRNA表达增加，部分依赖于膜启动的信号转导，导致通道功能增强和神经元兴奋性增强，这可能是E2促进爆发性放电和周期性GnRH神经分泌的机制之一。
T-type calcium channels are responsible for generating low-threshold spikes that facilitate burst firing and neurotransmitter release in neurons. GnRH neurons exhibit burst firing, but the underlying conductances are not known. Previously, we have found that 17β-estradiol (E2) increases T-type channel expression and excitability of hypothalamic arcuate nucleus neurons. Therefore, we used ovariectomized oil- or E2-treated EGFP-GnRH mice to explore the expression and E2-regulation of T-type channels in GnRH neurons. Based on single cell RT-PCR and real-time PCR quantification of the T-type channel α1-subunits, we found that all three subunits were expressed in GnRH neurons with Cav3.3≥Cav3.2>Cav3.1. The mRNA expression of the three subunits was increased with surge-inducing levels of E2 during the morning. During the afternoon, Cav3.3 mRNA expression remained elevated, whereas Cav3.1 and Cav3.2 were decreased. The membrane estrogen receptor agonist STX increased the expression of Cav3.3, but not Cav3.2 in GnRH neurons. Whole-cell patch recordings in GnRH neurons revealed that E2 treatment significantly augmented T-type current density at both time-points, and increased the rebound excitation during the afternoon. Although E2 regulated the mRNA expression of all three subunits in GnRH neurons, the increased expression combined with the slower inactivation kinetics of the T-type current indicates that Cav3.3 may be the most important for bursting activity associated with the GnRH/LH surge. The E2-induced increase in mRNA expression, which depends in part on membrane-initiated signaling, leads to increased channel function and neuronal excitability, and could be a mechanism by which E2 facilitates burst firing and cyclic GnRH neurosecretion.