Suprachiasmatic nucleus to kisspeptin circuit in the circadian control of reproduction

生物钟是生理和行为许多方面的基本调节器，包括 生殖生殖成功取决于控制生殖的神经内分泌活动的适当的每日时间 排卵下丘脑视前区（POA）的Kisspeptin（Kiss 1）神经元在这一过程中起关键作用。 通过驱动下游促性腺激素释放激素（GnRH）神经元的活动， 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计时的， 视交叉上核（SCN）在昼夜活动开始之前启动，确保排卵， 几个小时后发生的，与性行为相吻合。SCN的投影提供定时信号 GnRH神经元网络，包括POA Kiss 1神经元。事实上，报告表明，精氨酸 表达加压素（AVP）的SCN神经元可能通过激活POA在每日峰电位的时间中起关键作用 Kiss 1神经元。我们先前发表的研究提供了SCN投射释放AVP刺激POA的证据 Kiss 1神经元电活动，并且该回路在当天驱动Kiss 1神经元活动最有效 发生浪涌。最近，我们获得了令人兴奋的初步数据，表明一个独特的SCN 群体释放GABA并抑制Kiss 1神经元活性。这些新的观察结果，沿着我们发表的 工作，揭示SCN神经元可以双向控制Kiss 1神经元的电活动，通过 释放GABA和AVP。这使我们假设SCN衍生的AVP平衡的变化- 介导的兴奋和GABA介导的抑制有助于门控POA Kiss 1神经元的激活， 激增 我们将采用解剖和功能相结合的方法来解决这个中心问题。 假说.我们的第一个目标将是建立SCN神经元直接投射和释放GABA的POA Kiss 1神经元的脑切片电生理学和光遗传学研究。此外，我们将确定函数 GABA释放对Kiss 1神经元电活动的影响。第二个目标，我们将 使用追踪和免疫组织化学方法来确定SCN神经元投射靶向那些 POA Kiss 1细胞参与了激增，并决定了这些细胞的身份。 预测以及他们的激活模式之前的激增。在我们的第三个目标中，我们将首先评估电气 SCN神经元群在排卵前高峰前数小时的活动。利用这些信息， 然后，我们将确定Kiss 1神经元如何整合SCN定时信号，通过GABA和AVP介导 在增兵的那天，总之，这项研究将提供有关昼夜节律控制的新信息， 生殖，特别是触发排卵的神经内分泌事件的每日时间。更好的 了解负责生理条件下这些回路的昼夜节律调节的神经机制 这些条件可能为排卵功能障碍的潜在未来治疗开辟新的途径。

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.