Role of HCN1 channels in the function and malfunction of parvalbumin positive interneurons

项目概要 最近的临床发现表明编码超极化激活的基因发生了新突变 严重儿童癫痫中的 HCN1 阳离子通道。同时全基因组关联 研究表明 HCN1 基因座与精神分裂症密切相关。在此我们旨在提供详细的 表征 HCN1 在正常神经功能中的作用，并确定 HCN1 如何致病 突变扰乱神经活动，导致大脑功能紊乱。 HCN1 通道的不同寻常之处在于它们 被膜超极化激活，但传导内向去极化 Na /K 电流，并表现出 它们表达的不同神经元类别中亚细胞定位的对比模式。 因此，该通道在海马 CA1 和新皮质第 5 层锥体神经元中强烈表达，其中 它的目标是顶端树突，其密度随距树突距离的增加而显着增加。 索玛。 HCN1 在小白蛋白阳性抑制性神经元 (PV IN) 中也强烈表达，相反， 对于锥体神经元，它的目标是 PV IN 轴突和突触前末梢。对具有一般或 前脑限制性 HCN1 基因缺失揭示了该通道作为负性通道的重要作用。 海马锥体神经元树突整合和长期突触可塑性的约束，以及 海马依赖性空间记忆。 HCN1 缺失会降低锥体神经元位置细胞的精确度 空间编码，同时增加空间表示的稳定性。与经过充分研究的角色相比 HCN1在锥体神经元中的功能，目前对于HCN1在抑制性神经元中的作用知之甚少。这个 由于缺乏信息，无法充分了解 HCN1 如何促进正常的大脑功能和 考虑到抑制性神经元，尤其是 PV IN 在这些过程中的重要性。此外， 因为在检查的 HCN1 敲除小鼠中，HCN1 从兴奋性和抑制性神经元中都被删除了 迄今为止，所报告的学习和记忆以及体内放电特性的改变在多大程度上反映了 HCN1 在兴奋性神经元和抑制性神经元中的作用尚不清楚。在我们的申请中，我们建议审查 详细介绍了 HCN1 如何在细胞、体内网络和行为水平上促进 PV IN 功能。我们会 由此探讨：野生型HCN1在调节PV IN内在兴奋性和突触前功能中的作用（Aim 1）； PV IN 功能如何受到癫痫相关 HCN1 突变的干扰（目标 3a）；如何选择性删除 PV IN 中的野生型 HCN1 改变了空间信息以及空间和非空间信息的体内编码 记忆行为（目标 2）；以及某些抗癫痫药物增加癫痫发作的矛盾作用 携带癫痫相关 HCN1 突变的小鼠（目标 3b）。我们这些研究的目标是提供 关于特定类别神经元中表达的给定通道如何对大脑做出贡献的基本信息 功能，并提供对疾病机制的新见解，从而可能提出新的治疗方法。

Project Summary Recent clinical findings implicate de novo mutations in the gene encoding the hyperpolarization-activated HCN1 cation channel in severe forms of childhood epilepsy. At the same time genome-wide association studies demonstrate a strong link of the HCN1 locus with schizophrenia. Here we aim to provide a detailed characterization of the role of HCN1 in normal neural function, and to determine how disease-causing HCN1 mutations perturb neural activity to generate disordered brain function. HCN1 channels are unusual in that they are activated by membrane hyperpolarization, yet conduct an inward depolarizing Na+/K+ current, and show a contrasting pattern of subcellular localization in the distinct classes of neurons in which they are expressed. Thus, the channel is strongly expressed in hippocampal CA1 and neocortical layer 5 pyramidal neurons, where it is targeted to the apical dendrites in a striking gradient of increasing density with increasing distance from the soma. HCN1 is also strongly expressed in parvalbumin-positive inhibitory neurons (PV INs), where, in contrast to pyramidal neurons, it is targeted to PV IN axons and presynaptic terminals. Studies of mice with a general or forebrain-restricted genetic deletion of HCN1 have revealed the important role of this channel as a negative constraint of hippocampal pyramidal neuron dendritic integration and long-term synaptic plasticity, and of hippocampal-dependent spatial memory. Loss of HCN1 decreases the precision of pyramidal neuron place cell spatial coding while increasing the stability of spatial representations. In contrast to the well-studied role of HCN1 in pyramidal neuron function, relatively little is known about the role of HCN1 in inhibitory neurons. This lack of information prevents a full appreciation as to how HCN1 contributes to both normal brain function and disease, given the importance of inhibitory neurons, and PV INs in particular, in these processes. In addition, because HCN1 was deleted from both excitatory and inhibitory neurons in the HCN1 knockout mice examined to date, the extent to which the reported alterations in learning and memory and in vivo firing properties reflect the role of HCN1 in excitatory versus inhibitory neurons is unclear. In our application we propose to examine in detail how HCN1 contributes to PV IN function at the cellular, in vivo network, and behavioral levels. We will thus explore: the role of wild-type HCN1 in regulating PV IN intrinsic excitability and presynaptic function (Aim 1); how PV IN function is perturbed by epilepsy-associated HCN1 mutations (Aim 3a); how selective deletion of wild-type HCN1 from PV INs alters the in vivo coding of spatial information, as well as spatial and non-spatial memory behavior (Aim 2); and the paradoxical effects of certain anti-epileptic drugs to increase seizures in mice harboring epilepsy-associated HCN1 mutations (Aim 3b). Our goal in these studies is to both provide basic information about how a given channel expressed in a specific class of neurons contributes to brain function, and to provide new insights into disease mechanisms that may suggest new therapeutic approaches.