Work during the last decade has led to a novel hypothesis for a question that is half a century old: how is the secretory activity of GnRH neurons synchronized to produce episodic GnRH secretion. This hypothesis posits that a group of neurons in the arcuate nucleus (ARC) that contain kisspeptin, neurokinin B (NKB), and dynorphin (known as KNDy neurons) fire simultaneously to drive each GnRH pulse. Kisspeptin is proposed to be the output signal to GnRH neurons with NKB and dynorphin acting within the KNDy network to initiate and terminate each pulse, respectively. This review will focus on the importance of neuroanatomical studies in general and, more specifically, on the work of Dr Marcel Amstalden during his postdoctoral fellowship with the authors, to the development and testing of this hypothesis. Critical studies in sheep that laid the foundation for much of the KNDy hypothesis included the report that a group of neurons in the ARC contain both NKB and dynorphin and appear to form an interconnected network capable of firing synchronously, and Marcel's observations that the NKB receptor is found in most KNDy neurons, but not in any GnRH neurons. Moreover, reports that almost all dynorphin-NKB neurons and kisspeptin neurons in the ARC contained steroid receptors led directly to their common identification as “KNDy” neurons. Subsequent anatomical work demonstrating that KNDy neurons project to GnRH somas and terminals, and that kisspeptin receptors are found in GnRH, but not KNDy neurons, provided important tests of this hypothesis. Recent work has explored the time course of dynorphin release onto KNDy neurons and has begun to apply new approaches to the issue, such as RNAscope in situ hybridization and the use of whole tissue optical clearing with light-sheet microscopy. Together with other approaches, these anatomical techniques will allow continued exploration of the functions of the KNDy population and the possible role of other ARC neurons in generation of GnRH pulses.

过去十年的工作为半个世纪以来的问题提出了一个新假设：GnRH 神经元的分泌活动如何同步以产生间歇性 GnRH 分泌。该假设假设弓状核 (ARC) 中的一组神经元同时激活以驱动每个 GnRH 脉冲，这些神经元包含 Kisspeptin、神经激肽 B (NKB) 和强啡肽（称为 KNDy 神经元）。Kisspeptin 被提议作为 GnRH 神经元的输出信号，NKB 和强啡肽在 KNDy 网络内分别启动和终止每个脉冲。本综述将重点关注一般神经解剖学研究的重要性，更具体地说，是 Marcel Amstalden 博士在与作者进行博士后研究期间对这一假设的发展和检验的工作。为大部分 KNDy 假设奠定基础的绵羊的关键研究包括报告称，ARC 中的一组神经元同时包含 NKB 和强啡肽，并且似乎形成了一个能够同步发射的互连网络，以及 Marcel 的观察，即 NKB 受体是在大多数 KNDy 神经元中发现，但在任何 GnRH 神经元中都没有。此外，有报道称 ARC 中几乎所有的强啡肽-NKB 神经元和kisspeptin 神经元都含有类固醇受体，这直接导致它们被共同识别为“KNDy”神经元。随后的解剖工作证明 KNDy 神经元投射到 GnRH 胞体和末端，并且在 GnRH 中发现了kisspeptin 受体，但在 KNDy 神经元中没有，为这一假设提供了重要的检验。最近的工作探索了强啡肽释放到 KNDy 神经元的时间过程，并已开始应用新方法来解决这个问题，例如 RNAscope 原位杂交和使用全组织光学透明与光片显微镜。与其他方法一起，这些解剖技术将允许继续探索 KNDy 群体的功能以及其他 ARC 神经元在 GnRH 脉冲生成中的可能作用。