Control of Circuit Hyperexcitability by Endogenous Opioids in Epilepsy

癫痫是一种毁灭性的神经疾病，影响着大约200万美国人，通常具有抵抗力。 去接受治疗。动物研究表明癫痫与代偿性疾病有关。 大脑的变化，包括神经元回路的异常重新连接。特别是，癫痫是 与海马体连接性改变有关，海马体是大脑的一个区域，经常是焦点 以引发癫痫发作。与癫痫相关的一种特殊的海马区回路重排 涉及海马区颗粒细胞轴突(苔藓纤维)逆行生长(“发芽”)。 这些发芽的纤维可通过形成反复的兴奋性直接导致海马区的过度兴奋性。 或者增加抑制机制的活性，防止癫痫发作。 使用新方法的组合，我们最近的工作确定了这些纤维直接驱动 逆激和超激电路功能。有趣的是，这些逆行中的很大一部分 投射来自新生的、成体出生的颗粒细胞神经元，这些神经元大量产生。 癫痫发作后，经历异常成熟和电路整合。这表明这些成年出生的 神经元可能对癫痫的启动和传播有很大的贡献，如果它们改变了 海马区的兴奋和抑制。 同时，人们早就知道发芽的苔藓纤维可以产生多种多肽。 神经递质，包括内源性阿片肽。尽管这些多肽的受体是 已知能有效控制整个大脑的神经元兴奋性，内源性的功能重要性 多肽在控制癫痫患者的过度兴奋性方面还没有被探索过。值得注意的是，即使是基本的问题 关于这些多肽释放的条件，特定受体的功能在 不同的细胞类型，以及这些多肽是否调节癫痫的发作频率或严重程度 为人所知。因此，它们在癫痫发生过程中的作用仍然是该领域长期悬而未决的问题。 代表着一个治疗的机会。 通过这项提议，我们将回答有关这些多肽在 癫痫患者海马区功能的控制，以及阿片肽信号的潜在变化 增强神经发生的机制可能会压倒内源性控制机制，从而阻止 癫痫发作。我们结合了不同品系的转基因小鼠，这使得我们能够专门标记和 光遗传学控制活组织中不同亚群的海马体颗粒细胞。我们会引诱 采用已建立的匹罗卡品癫痫模型进行实验性癫痫的研究，并采用电生理学方法 研究这些多肽在海马区回路中的功能作用的记录技术。此外，我们 将使用额外的基因操作来改变癫痫患者多肽释放细胞的电活动 在活体小鼠身上，以确定这如何影响癫痫发作。 我们的工作将提供对阿片信号在癫痫中的作用的见解，并使我们能够确定 不同的颗粒细胞是否发芽对海马神经元的兴奋性有不同的调节作用。这 将回答有关获得性癫痫发病机制的长期问题，通过直接定义 发芽苔藓纤维通路的功能作用及其各种多肽信号机制。一个 了解阿片类药物控制海马区兴奋性的机制可能导致一种新的 潜在地预防神经元损伤后癫痫发作的治疗方法。

Epilepsy is a devastating neurologic condition that affects about 2 million Americans and is often resistant to medical treatment. Animal studies have demonstrated that epilepsy is associated with compensatory changes in the brain, which includes the aberrant rewiring of neuronal circuits. In particular, epilepsy is associated with altered connectivity in the hippocampus, a region of the brain that is frequently the focal point for the initiation of seizures. One particular hippocampal circuit rearrangement associated with epilepsy involves the growth (“sprouting”) of hippocampal granule cell axons (the mossy fibers) in a retrograde direction. These sprouted fibers could directly cause hippocampal hyperexcitability by forming recurrent excitatory circuits, or alternatively increase the activity of inhibitory mechanisms and prevent seizures. Using a combination of novel approaches, our recent work determined that these fibers directly drive retrograde excitation and hyperexcitable circuit function. Interestingly, a large proportion of these retrograde projections derive from newly generated, adult-born granule cell neurons, which are produced in large numbers after seizures and undergo aberrant maturation and circuit integration. This suggests that these adult-born neurons might contribute substantially to seizure initiation and propagation, if they alter the balance of excitation and inhibition in the hippocampus. At the same time, sprouted mossy fibers have long been known to produce multiple peptide neurotransmitters, which include endogenous opioid peptides. Although the receptors for these peptides are known to potently control neuronal excitability throughout the brain, the functional importance of endogenous peptides in the control of hyperexcitability in epilepsy has not been explored. Notably, even basic questions regarding the conditions under which these peptides are released, the functions of specific receptors in different cell types, and whether these peptides modulate seizure frequency or severity in epilepsy are not known. Thus, their role during epileptogenesis remains a long-standing unanswered question in the field, and represents a therapeutic opportunity. With this proposal, we will answer fundamental questions regarding the roles of these peptides in the control of hippocampal function in epilepsy, and how potential alterations in opioid peptide signaling mechanisms due to enhanced neurogenesis might overwhelm endogenous control mechanisms that prevent seizures. We have combined various lines of genetically modified mice, which allow us to specifically label and optogenetically control different subsets of hippocampal granule cells in live tissue. We will induce experimental epilepsy using the well-established pilocarpine model of epilepsy, and use electrophysiologic recording techniques to study the functional roles of these peptides in the hippocampal circuit. Furthermore, we will use additional genetic manipulations to modify the electrical activity of peptide-releasing cells in epileptic mice in vivo, to determine how this affects seizures. Our work will provide insights into the function of opioid signaling in epilepsy, and allow us to determine whether sprouting from various cohorts of granule cells differentially modulates hippocampal excitability. This will answer long-standing questions regarding the pathogenesis of acquired epilepsy, by directly defining the functional role of the sprouted mossy fiber pathway and its various peptide signaling mechanisms. An understanding of the mechanisms through which opioids control hippocampal excitability could lead to a novel therapeutic approach to potentially prevent seizures after neuronal injury.