Suprachiasmatic nucleus to kisspeptin circuit in the circadian control of reproduction

生物钟是许多生理和行为方面的基本调节器，包括 繁殖。生殖成功取决于每天适当的神经内分泌事件的时机，这些事件控制着 排卵。下丘脑视前区(POA)的Kispeptin(Kiss1)神经元在这一过程中起着关键作用 通过驱动下游促性腺激素释放激素(GnRH)神经元的活动来产生 促性腺激素释放激素和促黄体生成素分泌，触发排卵。啮齿动物的激增是由中央生物钟在 视交叉上核(SCN)在昼夜活动开始前启动，确保排卵， 这发生在几个小时后，与性行为不谋而合。来自SCN的投影提供定时信号 GnRH神经元网络，包括POA Kiss1神经元。事实上，有报道表明精氨酸 加压素(AVP)表达的SCN神经元可能通过激活POA在每天的电涌时间中发挥关键作用 Kiss1神经元。我们之前发表的研究提供了证据表明，SCN投射释放AVP来刺激POA Kiss1神经元的电活动，并且这个电路在驱动Kiss1神经元活动的当天是最有效的 浪涌就会发生。最近，我们获得了令人兴奋的初步数据，表明一种不同的SCN 群体释放GABA并抑制Kiss1神经元的活动。这些新的观察结果，以及我们发表的 工作发现，SCN神经元可能双向控制Kiss1神经元的电活动，通过 释放GABA和AVP。这导致我们假设，SCN来源的AVP平衡的变化- 介导的兴奋和GABA介导的抑制有助于门控POA Kiss1神经元的激活 这股风潮。 我们将采用解剖学和功能学相结合的方法来解决这个中心问题 假设。我们的第一个目标是建立SCN神经元直接投射到POA并在POA上释放GABA Kiss1神经元使用脑片电生理学和光遗传学。此外，我们将确定功能 GABA释放对发情周期Kiss1神经元电活动的影响在第二个目标中，我们将 使用束追踪和免疫组织化学方法来确定SCN神经元的投射针对这些 参与电涌的POA Kiss1细胞，并确定贡献这些细胞的身份 预测以及它们在激增之前的激活模式。在我们的第三个目标中，我们将首先评估电气 排卵前高峰前几个小时内SCN神经元群体的活动。利用这些信息， 然后我们将确定Kiss1神经元如何整合通过GABA和AVP介导的SCN定时信号 释放，在增兵的当天。总之，这项研究将提供有关昼夜节律控制的新信息 生殖，特别是每天触发排卵的神经内分泌事件的时间。更好的 了解生理状态下负责这些回路昼夜节律的神经机制 这些情况可能会为未来排卵功能障碍的潜在治疗开辟新的途径。

The circadian clock is a fundamental regulator of many aspects of physiology and behavior, including reproduction. Reproductive success depends on appropriate daily timing of neuroendocrine events that control ovulation. Kisspeptin (Kiss1) neurons in the preoptic area (POA) of the hypothalamus play a critical role in this by driving the activity of downstream gonadotropin-releasing hormone (GnRH) neurons to generate the surge in GnRH and LH secretion that triggers ovulation. The surge in rodents is timed by the central circadian clock in the suprachiasmatic nucleus (SCN) to initiate just before the onset of diurnal activity, ensuring that ovulation, which occurs a few hours later, coincides with sexual behavior. Projections from the SCN provide timing signals to the GnRH neuronal network, including to POA Kiss1 neurons. Indeed, reports indicate that arginine vasopressin (AVP)-expressing SCN neurons may play a key role in daily timing of the surge by activating POA Kiss1 neurons. Our prior published studies provide evidence that SCN projections release AVP to stimulate POA Kiss1 neuron electrical activity, and that this circuit is most effective in driving Kiss1 neuron activity on the day the surge occurs. Recently, we have obtained exciting preliminary data that indicate that a distinct SCN population releases GABA and inhibits Kiss1 neuron activity. These new observations, along with our published work, reveal that SCN neurons may bidirectionally control the electrical activity of Kiss1 neurons, through the release of GABA and AVP. This has led us to hypothesize that a shift in the balance of SCN-derived AVP- mediated excitation and GABA-mediated inhibition contributes to gating the activation of POA Kiss1 neurons for the surge. We will employ a combination of anatomical and functional approaches to address this central hypothesis. Our first aim will be to establish that SCN neurons directly project to and release GABA on POA Kiss1 neurons using brain slice electrophysiology and optogenetics. Further, we will determine the functional impact of GABA release on Kiss1 neuron electrical activity across the estrous cycle. In the second aim, we will use tract-tracing and immunohistochemical approaches to establish that SCN neuron projections target those POA Kiss1 cells that are involved in the surge and determine the identity of the cells that contribute these projections as well as their activation patterns prior to the surge. In our third aim, we will first assess the electrical activity of SCN neuronal populations in the hours that precede the preovulatory surge. Using this information, we will then determine how Kiss1 neurons integrate SCN timing signals, mediated through GABA and AVP release, on the day of the surge. Together, this research will provide new information about the circadian control of reproduction, and specifically the daily timing of the neuroendocrine events that trigger ovulation. A better understanding of the neural mechanisms responsible for circadian regulation of these circuits under physiological conditions may open new avenues for potential future treatments of ovulatory dysfunction.