Role of CCK-positive perisomatic inhibitory neurons in the generation of normal and pathological network oscillations in the mouse hippocampus

体周抑制在同步许多脑区的网络活动中起着关键作用。在过去的几十年里，啮齿动物海马已经成为研究突触抑制和可塑性的重要模型，作为网络振荡的基本机制。海马主要神经元的体周抑制主要由小白蛋白（PV）阳性和胆囊收缩素（CCK）阳性的中间神经元（IN）提供。这两种类型的IN有很大程度上相似的传入和传出连接，并协同作用，提供反馈和前馈抑制。然而，它们在参与振荡活动方面有所不同。PV阳性细胞主要参与高频活动（尖波波纹（SPWR）和γ振荡），而CCK阳性IN参与低频θ振荡。这种差异行为的原因尚不清楚。在这里，我们提出CCK阳性神经元的一个独特的性质，即GABA的异步释放，是它们在局部网络活动中发挥作用的基本机制。我们认为，这一特征（1）减少了它们参与高频事件，（2）使它们适合于产生低频振荡，（3）在预防癫痫样活动中至关重要。在这个项目中，我们将研究CCK阳性的Ins和GABA的异步释放在正常和病理海马网络振荡的产生和终止中的作用。我们将在体外使用各种现代工具操纵GABA从CCK IN末端的释放。在野生型小鼠中，这两种类型的IN的活性将通过位于突触前的G蛋白偶联受体的激动剂或拮抗剂、通过膜片钳移液管引入钙缓冲液以及通过干扰突触前钙排出泵来选择性地调节。在具有特异性靶向CCK阳性IN的小鼠中，将使用病毒载体引入化学遗传学试剂（伊维菌素敏感突变型GlyR-α 1受体）、遗传编码的钙缓冲液或光遗传学工具。结合细胞和网络行为的电生理学分析，这些方法将使我们能够选择性地评估CCK阳性神经元在正常和病理状态下海马节律产生中的差异参与。

Perisomatic inhibition plays a key role in synchronizing network activity in many brain regions. In the last few decades, the rodent hippocampus has become an important model for studying synaptic inhibition andplasticity as fundamental mechanisms underlying network oscillations. Perisomatic inhibition of hippocampal principal neurons is mainly provided by parvalbumin (PV)-positive and cholecystokinin(CCK)-positive interneurons (INs). Both types of IN have largely similar afferent and efferent connectivity and act synergistically in providing feedback and feedforward inhibition. They differ, however, in their involvement in oscillatory activity. PV-positive cells arecruciallyinvolved in high-frequency activity (sharp wave ripples (SPWRs) and gamma oscillations) while CCK-positive INs are involved in low frequency theta oscillations. The reasons for this differential behavior are not clear. Here we propose that a unique property of CCK-positive INs, namely asynchronous releaseof GABA, is a fundamental mechanismunderlying their role in local network activity. We suggest that this feature (1) diminishes their involvement in high frequency events, (2) makes them suitable for generation of low frequency oscillations, and (3) is crucial in prevention of epileptiform activity. In the proposed project, we will study the role of CCK-positive Ins and asynchronous GABA release in the generation and termination of normal and pathological hippocampal network oscillations. We will manipulate GABA release from CCK IN terminals in vitro, using a variety of modern tools. In wild-type mice, the activity of the two types of INwillbe selectively modulated by agonists or antagonists of presynaptically located G-protein-coupled receptors, by introductionof calcium buffers via a patch clamp pipette, and by interfering with the presynaptic calcium extrusion pumps. In mice with specifically targeted CCK-positive INs, viral vectors will be used to introduce chemogenetic agents (ivermectin-sensitive mutant GlyR-alpha1 receptors), genetically encoded calcium buffers, or optogenetictools. Together with electrophysiological analysis of cellular and network behavior, these approaches will allow us to selectively evaluatethe differential involvement of CCK-positive INs in the generation of hippocampal rhythms in normal and pathological states.