Xu Chun, Roepke Troy A, Zhang Chunguang, Rønnekleiv Oline K, Kelly Martin J
Department of Physiology and Pharmacology, Oregon National Primate Research Center, Oregon Health and Science University, Portland, Oregon 97239, USA.
Endocrinology. 2008 May;149(5):2459-66. doi: 10.1210/en.2007-1178. Epub 2008 Jan 24.
GnRH autoregulates GnRH neurons through an ultrashort feedback loop. One potential mechanism is the regulation of K(+) channel activity through the GnRH receptor. Whereas GnRH inhibits the activity of the M-current in peripheral neurons, there is no direct evidence that the M-current is involved in the autoregulatory pathway of GnRH or if the M-current is expressed in GnRH neurons. The M-current is a noninactivating, subthreshold K(+) current that inhibits cell excitability and is ubiquitously expressed in the central nervous system. We found that GnRH neurons expressed the neuronal M-current subunits, KCNQ2, -3, and -5 in addition to GnRH receptor (GnRH R1). Therefore, using whole-cell patch clamp recording and single-cell RT-PCR, we explored the effects of mammalian GnRH peptide on enhanced green fluorescent protein-tagged GnRH neurons acutely dispersed as well as in slice preparations. GnRH (100nm) inhibited GnRH neuronal excitability by hyperpolarizing the membrane. In the presence of CdCl(2), BaCl(2), and tetrodotoxin, GnRH activated an outward current in a dose-dependent manner (EC(50) 11 nm) in 30% of GnRH neurons. In voltage clamp, the selective M-channel blocker, XE-991, inhibited a K(+) current in GnRH neurons. XE-991 also antagonized the outward K(+) current induced by GnRH. Moreover, the GnRH effects on the M-current were blocked by the GnRH R1 antagonist antide. Therefore, these findings indicate that GnRH activates the M-current in a subpopulation of GnRH neurons via GnRH R1. This ultrashort circuit is one potential mechanism by which GnRH could modulate its own neuronal excitability through an autoreceptor.
促性腺激素释放激素（GnRH）通过超短反馈回路对GnRH神经元进行自身调节。一种潜在机制是通过GnRH受体调节钾离子通道活性。虽然GnRH抑制外周神经元中M电流的活性，但没有直接证据表明M电流参与GnRH的自身调节途径，也没有证据表明GnRH神经元中表达M电流。M电流是一种非失活的阈下钾电流，可抑制细胞兴奋性，在中枢神经系统中广泛表达。我们发现，除了GnRH受体（GnRH R1）外，GnRH神经元还表达神经元M电流亚基KCNQ2、-3和-5。因此，我们使用全细胞膜片钳记录和单细胞逆转录聚合酶链反应（RT-PCR），研究了哺乳动物GnRH肽对急性分散的以及脑片中增强型绿色荧光蛋白标记的GnRH神经元的影响。GnRH（100 nM）通过使膜超极化来抑制GnRH神经元的兴奋性。在存在氯化镉（CdCl₂）、氯化钡（BaCl₂）和河豚毒素的情况下，GnRH以剂量依赖方式（半数有效浓度[EC₅₀]为11 nM）激活了30%的GnRH神经元中的外向电流。在电压钳实验中，选择性M通道阻滞剂XE-991抑制了GnRH神经元中的钾电流。XE-991还拮抗了GnRH诱导的外向钾电流。此外，GnRH对M电流的作用被GnRH R1拮抗剂antide阻断。因此，这些发现表明GnRH通过GnRH R1激活了一部分GnRH神经元中的M电流。这种超短回路是GnRH通过自身受体调节其自身神经元兴奋性的一种潜在机制。
