The gonadotropin-releasing hormone (GnRH) neuron is the pivotal control center in a tightly regulated reproductive axis. The release of GnRH controls estradiol production by the ovary, and estradiol acts at the hypothalamus to regulate GnRH release. However, the mechanisms of estradiol feedback are just beginning to be understood. We have previously shown that estradiol administered to the female mouse modulates sodium currents in fluorescently-labeled GnRH neurons. In the current studies, estradiol (1 nM) was applied directly, for 16-24h, to hypothalamic cultures from young or aged female ovariectomized mice. The direct application of estradiol modulated a tetrodotoxin-sensitive sodium current in isolated GnRH neurons from both young and aged animals. Estradiol, and the specific estrogen receptor-β agonist DPN, decreased current amplitude measured in the morning (AM), but had no effect on afternoon currents. These compounds also decreased the rise and decay slope of the current response, increased the width of the current, and increased action potential width in AM recordings. In addition, estradiol decreased the amplitude of the depolarizing afterpotential (DAP); this effect was not time-of-day dependent. The ER-β agonist DPN did not mimic the effect of estradiol on DAPs, and the modulation of DAPs by estradiol was no longer present in cells from postreproductive animals. These results indicate that estradiol can affect the physiology of GnRH neurons via multiple pathways that are differentially regulated during the transition to reproductive senescence, suggesting that estradiol regulation of GnRH neuronal output is modulated during the aging process.
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