Synchronous Activity in Hybrid Neuronal Microcircuits

描述（由申请人提供）：为了从机制上理解脑功能，从而采取原则性的方法来修复受损的脑，生物医学科学家面临着弥合单细胞的电生理特性和神经元网络的涌现特性之间的差距的艰巨任务。这些实验将有助于弥合这一差距，解决一个与认知、学习和记忆密切相关的问题：海马体中连贯θ节律的细胞基础。核心假设是，一类特殊的海马抑制性中间神经元，称为oriens lacunosum-moleculare（O-LM）细胞，在体内放大θ节律和体外产生θ节律活动中起着至关重要的作用。拟议的脑切片实验依赖于最近开发的实时动态箝位系统来研究O-LM细胞的整合特性，并将活神经元浸入计算机模拟的微电路中。构建这样的混合微电路--包含生物和模拟神经元的小型脑电路，它们在真实的时间内相互作用--允许人们以前所未有的定量严格性来测试微电路功能的精确假设。其他拟议的研究集中在O-LM-细胞投射到锥体细胞的远端树突的后果，以及O-LM-细胞损失在体内和体外的θ节律的后果。本研究计划有五个目的：（1）研究O-LM细胞在模拟活体状态的人工突触屏障作用下的输入输出特性。(2)目的：研究相位锁定、远端和近端抑制性输入如何导致兴奋性锥体细胞的相位锁定稀疏放电。(3)目的：研究远端O-LM抑制对锥体神经元树突输入时相依赖性选择的影响。(4)研究从定向-腔隙-分子（O-LM）中间神经元到锥体细胞和快速发放中间神经元的输入如何在“闭环”网络中促进自组织θ和γ节律。(5)研究在反馈输入、隔区人工节律驱动等因素的作用下，O-LM细胞节律活动同步化的重要性。这项研究计划的长期目标是以定量和机械的严谨性来理解海马和其他皮质区域出现正常和异常节律行为的机制。这项工作将直接关系到理解θ和伽马节律。这两种连贯活动模式似乎对正常认知、学习和记忆至关重要，并且在包括癫痫、精神分裂症、帕金森病和阿尔茨海默病在内的广泛疾病中被破坏。由于所提出的方法可以显示特定的膜机制如何有助于网络功能，因此它对于识别新的药物靶点特别有用。所提出的方法的一个额外好处是，为这些研究开发的动态钳技术可能被证明对大脑的治疗性反馈控制电刺激有用。

DESCRIPTION (provided by applicant): To understand brain function mechanistically, and thus to take principled approaches in repairing damaged brains, biomedical scientists face the daunting task of bridging the gap between the electrophysiological properties of single cells and the emergent properties of neuronal networks. The proposed experiments will help bridge this gap for a problem of great relevance in cognition and learning and memory: the cellular bases of the coherent theta rhythm in the hippocampus. The central hypothesis is that a particular class of hippocampal inhibitory interneurons, called oriens lacunosum-moleculare (O-LM) cells, plays a crucial role in amplifying the theta rhythm in vivo and generating theta-rhythmic activity in vitro. Proposed brain-slice experiments rely upon a recently developed real-time dynamic clamp system to study the integrative properties of O-LM cells and to immerse living neurons in computer-simulated microcircuits. Building such hybrid microcircuits-small brain circuits containing biological and simulated neurons that interact in real time- allows one to test precise hypotheses of microcircuit function with unprecedented quantitative rigor. Additional proposed studies focus on the consequences of O-LM-cell projections to the distal dendrites of pyramidal cells, as well as the consequences of O-LM-cell loss for the theta rhythm in vivo and in vitro. The proposed research program has five aims: (1) To study the input-output properties of O-LM cells in response to artificial synaptic barrages that mimic the in vivo state. (2) To study how phase-locked, distal and proximal inhibitory inputs can lead to phase-locked sparse firing in excitatory pyramidal cells. (3) To study the effects of distal O-LM-based inhibition on phase-dependent selection of dendritic inputs to pyramidal neurons. (4) To study how input from oriens-lacunosum moleculare (O-LM) interneurons to pyramidal cells and fast- spiking interneurons contributes to self-organized theta and gamma rhythms in "closed-loop" networks. (5) To study the importance of synchronization of O-LM cells for rhythmic activity under manipulation of feedback input, artificial rhythmic drive from the septum, and other factors. The long-term goal of this research program is to understand, with quantitative and mechanistic rigor, the mechanisms by which both normal and abnormal rhythmic behaviors emerge in the hippocampus and other cortical regions. The work will be immediately relevant to understanding the theta and gamma rhythms. These two patterns of coherent activity seem crucial for normal cognition and learning and memory, and are disrupted in a broad range of conditions including epilepsy, schizophrenia, Parkinson's disease, and Alzheimer's disease. Because the proposed approach can show how specific membrane mechanisms contribute to network function, it is particularly useful for identifying new drug targets. An added bonus of the proposed approach is that the dynamic clamp technology developed for these studies may prove useful for therapeutic, feedback-controlled electrical stimulation of the brain.