Contribution of interneuron types to the emergence of fast network activity patterns in the mouse dentate gyrus

神经元网络的节律性活动以0.5至300 Hz的各种频率发生。 在这个宽的频率范围内，特别是θ-（6-10 Hz）调制的γ（30-130 Hz）振荡吸引了最高的关注，因为它们与同步活动的细胞组装体的信息编码、存储和回忆的功能关系是最明显的。在齿状回，作为海马体的输入门，θ调制的伽马活动是必不可少的空间导航和获取新的意识记忆在人类和啮齿动物。这里，伽马活动模式出现在两个空间、时间和光谱上不同的区域中，作为在整个齿状回中全局发生的30-75 Hz的低伽马，以及作为在75-150 Hz的空间上更受限的局灶性高伽马活动（Strüber等人，2017; Lastoci & Klausberger，2017）。与此相反，高伽玛在齿状回是不相关联的其余海马子字段，表明它是局部限制到齿状回的子网络。这样的局部高频伽马活动可以允许对输入信息的局部处理以及将信息流隔离到非重叠存储器中。因此，局部高伽马活性可能会增加齿状回的存储容量。然而，支持齿状回产生伽马振荡的电路机制在很大程度上仍是未知的。在这里，我们的目标是解决这个基本问题，首先，记录动作电位从海马颗粒细胞（GC），齿状回的主要细胞，和GABA能抑制性中间神经元，通过从暴露于虚拟现实的头部固定的非麻醉小鼠的齿状回中的单个细胞进行单细胞记录。其次，我们将在记录过程中用染料填充细胞，用于随后的形态学和免疫组织化学鉴定。第三，通过分析的时间关系的单个动作电位的阶段的细胞外记录的节律场电位，我们的目标是研究的差异，在各种神经元类型的贡献θ以及慢和快的伽马活动模式。我们相信，这一跨学科研究的结果将提供新的信息，在啮齿动物齿状回的theta调制的伽马振荡的产生的细胞机制，从而将提高我们的认知功能的中间神经元的作用的理解。

Rhythmic activities of neuronal networks occur at various frequencies ranging from 0.5 up to 300 Hz. In this broad frequency range, particularly theta- (6-10 Hz) modulated gamma (30-130 Hz) oscillations attracted highest attention because their functional relationship to coding, storing and recall of information by synchronously active cell assemblies is most evident. In the dentate gyrus, as the input gate of the hippocampus, theta-modulated gamma activity is essential for spatial navigation and acquisition of new conscious memories in humans and rodents. Here, gamma activity patterns emerge in two spatially, temporally and spectrally distinct regimes, as low gamma at 30-75 Hz, occurring globally in the entire dentate gyrus, and as focal more spatially restricted high gamma activities at 75-150 Hz (Strüber et al., 2017; Lastoci & Klausberger, 2017). In contrast, high gamma in the dentate gyrus is not phase correlated to the remaining hippocampal subfields indicating that it is locally restricted to subnetworks of the dentate gyrus. Such local high-frequency gamma activities may allow local processing of incoming information and the segregation of information streams into non-overlapping memories. Thus, local high gamma activity may increase storage capacity of the dentate gyrus. The circuit mechanisms that may support the generation of gamma oscillations in the dentate gyrus remain, however, largely unknown. Here we aim to address this fundamental problem by first, recording action potentials from glutamatergic granule cells (GCs), the principal cells of the dentate gyrus, and GABAergic inhibitory interneurons by performing juxtacellular recordings from individual cells in the dentate gyrus of head-fixed non-anaesthetized mice exposed to a virtual reality. Second, we will fill cells during recording with a dye for subsequent morphological and immunohistochemical identification. Third, by analyzing the temporal relationship of single action potentials to the phases of the extracellularly recorded rhythmic field potentials, we aim to examine differences in the contribution of the various neuron types to theta as well as slow and fast gamma activity patterns. We believe that the results of this interdisciplinary research will provide new information on the cellular mechanisms underlying the generation of theta-modulated gamma oscillations in the rodent dentate gyrus and thereby will improve our understanding on the role of interneurons in cognitive functions.