Control of Circuit Hyperexcitability by Endogenous Opioids in Epilepsy

癫痫是一种破坏性的神经系统疾病，影响约200万美国人， 接受治疗动物研究表明，癫痫与代偿性 大脑的变化，包括神经元回路的异常重新布线。特别是，癫痫是 与海马体的连接改变有关，海马体是大脑的一个区域，经常是焦点， 癫痫发作的诱因一种与癫痫相关的特殊海马回路重排 涉及海马颗粒细胞轴突（苔藓纤维）在逆行方向上的生长（“发芽”）。 这些出芽的神经纤维可通过形成反复的兴奋性突触，直接引起海马的过度兴奋。 电路，或者增加抑制机制的活性并防止癫痫发作。 使用新方法的组合，我们最近的工作确定这些纤维直接驱动 逆行兴奋和过度兴奋回路功能。有趣的是，这些逆行的大部分 投射来源于新产生的成年颗粒细胞神经元，它们大量产生 癫痫发作后，并经历异常成熟和电路整合。这表明这些成年人 神经元可能有助于实质性癫痫发作的启动和传播，如果他们改变平衡， 海马体的兴奋和抑制。 同时，人们早就知道发芽的苔藓纤维可以产生多种肽 神经递质，包括内源性阿片肽。虽然这些肽的受体是 已知其有效地控制整个大脑的神经元兴奋性，内源性神经元兴奋性的功能重要性， 肽在控制癫痫过度兴奋中的作用尚未被探索。值得注意的是，即使是最基本的问题 关于这些肽释放的条件， 不同的细胞类型，以及这些肽是否调节癫痫发作的频率或严重程度， 知道的因此，它们在癫痫发生过程中的作用仍然是该领域长期未回答的问题， 是一个治疗的机会 有了这个提议，我们将回答关于这些肽在细胞中的作用的基本问题。 癫痫中海马功能的控制，以及阿片肽信号传导的潜在改变 由于增强的神经发生机制可能压倒内源性控制机制， 癫痫发作我们已经结合了各种转基因小鼠的品系，这使我们能够特异性地标记和 在活体组织中，海马颗粒细胞的不同亚群被光遗传学控制。我们将诱导 实验性癫痫采用成熟的匹鲁卡品癫痫模型，并采用电生理 记录技术来研究这些肽在海马回路中的功能作用。而且我们 将使用额外的遗传操作来修改癫痫患者的肽释放细胞的电活动， 小鼠体内，以确定这如何影响癫痫发作。 我们的工作将为癫痫中阿片信号的功能提供见解，并使我们能够确定 是否发芽从不同队列的颗粒细胞差异调节海马兴奋性。这 将回答关于获得性癫痫发病机制的长期存在的问题，通过直接定义 发芽苔藓纤维途径及其各种肽信号传导机制的功能作用。一个 了解阿片类药物控制海马兴奋性的机制可能会导致一种新的 治疗方法，以潜在地预防神经元损伤后的癫痫发作。

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.