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The Journal of Neuroscience, September 19, 2007, 27(38):10153-10164; doi:10.1523/JNEUROSCI.1657-07.2007

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Behavioral/Systems/Cognitive
Gonadotropin-Releasing Hormone Neurons Express K_ATP Channels That Are Regulated by Estrogen and Responsive to Glucose and Metabolic Inhibition

Chunguang Zhang,¹ Martha A. Bosch,¹ Jon E. Levine,⁴ Oline K. Rønnekleiv,^1,2,3 and Martin J. Kelly¹

¹Department of Physiology and Pharmacology, ²Department of Anesthesiology and Perioperative Medicine, and ³Division of Neuroscience, Oregon National Primate Research Center, Oregon Health and Science University, Portland, Oregon 97239, and ⁴Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208

Correspondence should be addressed to either Dr. Martin J. Kelly or Dr. Oline K. Rønnekleiv, Department of Physiology and Pharmacology, L334, Oregon Health and Science University, 3181 Southwest Sam Jackson Park Road, Portland, OR 97239, Email: kellym{at}ohsu.edu or Email: ronnekle{at}ohsu.edu

Gonadotropin-releasing hormone (GnRH) is released in a pulsatile manner that is dependent on circulating 17ß-estradiol (E2) and glucose concentrations. However, the intrinsic conductances responsible for the episodic firing pattern underlying pulsatile release and the effects of E2 and glucose on these conductances are primarily unknown. Whole-cell recordings from mouse enhanced green fluorescent protein-GnRH neurons revealed that the K_ATP channel opener diazoxide induced an outward current that was antagonized by the sulfonylurea receptor 1 (SUR1) channel blocker tolbutamide. Single-cell reverse transcription (RT)-PCR revealed that the majority of GnRH neurons expressed Kir6.2 and SUR1 subunits, which correlated with the diazoxide/tolbutamide sensitivity. Also, a subpopulation of GnRH neurons expressed glucokinase mRNA, a marker for glucose sensitivity. Indeed, GnRH neurons decreased their firing in response to low glucose concentrations and metabolic inhibition. The maximum diazoxide-induced current was approximately twofold greater in E2-treated compared with oil-treated ovariectomized females. In current clamp, estrogen enhanced the diazoxide-induced hyperpolarization to a similar degree. However, based on quantitative RT-PCR, estrogen did not increase the expression of Kir6.2 or SUR1 transcripts in GnRH neurons. In the presence of ionotropic glutamate and GABA_A receptor antagonists, tolbutamide depolarized and significantly increased the firing rate of GnRH neurons to a greater extent in E2-treated females. Finally, tolbutamide significantly increased GnRH secretion from the preoptic-mediobasal hypothalamus. Therefore, it appears that K_ATP channels and glucokinase are expressed in GnRH neurons, which renders them directly responsive to glucose. In addition, K_ATP channels are involved in modulating the excitability of GnRH neurons in an estrogen-sensitive manner that ultimately regulates peptide release.

Key words: Kir6.2; SUR1; diazoxide; tolbutamide; glucokinase; glucose responsive; metabolic stress; GnRH secretion

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Received Oct. 6, 2006; revised Aug. 1, 2007; accepted Aug. 2, 2007.

Correspondence should be addressed to either Dr. Martin J. Kelly or Dr. Oline K. Rønnekleiv, Department of Physiology and Pharmacology, L334, Oregon Health and Science University, 3181 Southwest Sam Jackson Park Road, Portland, OR 97239, Email: kellym{at}ohsu.edu or Email: ronnekle{at}ohsu.edu

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