Synchronous Activity in Hybrid Neuronal Microcircuits

描述(申请人提供)：为了从机制上了解大脑功能，从而采取原则性的方法修复受损的大脑，生物医学科学家面临着弥合单个细胞的电生理特性和神经元网络的新兴特性之间的差距的艰巨任务。拟议中的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：海马体中连贯的theta节奏的细胞基础。中心假设是，一类特殊的海马区抑制性中间神经元，称为东方腔隙分子细胞，在体内放大theta节律和在体外产生theta节律活动方面起着至关重要的作用。提出的脑片实验依赖于最近开发的实时动态钳制系统来研究O-LM细胞的综合特性，并将活的神经元浸入计算机模拟的微电路中。建造这样的混合微电路--包含生物神经元和模拟神经元的小型大脑电路，实时相互作用--使人们能够以前所未有的定量精确度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远端树突的后果，以及O-Lm细胞在体内和体外对theta节律的影响。提出的研究计划有五个目标：(1)研究O-LM细胞在模拟体内状态的人工突触撞击时的输入-输出特性。(2)研究锁相、远端和近端抑制性输入对兴奋性锥体细胞稀疏放电的影响。(3)研究以O-LM为基础的远端抑制对树突传入锥体神经元的时相选择的影响。(4)研究O-LM中间神经元对锥体细胞和快速放电中间神经元的输入如何参与“闭合”网络中自组织的theta和Gamma节律。(5)研究在反馈输入、隔区人工节律驱动等因素作用下O-LM细胞同步化对节律活动的影响。这项研究计划的长期目标是，以定量和机械的严谨性，了解在海马体和其他皮质区域出现正常和异常节律行为的机制。这项工作将直接与理解theta和Gamma节律相关。这两种连贯的活动模式似乎对正常的认知和学习记忆至关重要，并在包括癫痫、精神分裂症、帕金森病和阿尔茨海默病在内的广泛情况下受到干扰。由于所提出的方法可以显示特定的膜机制如何对网络功能做出贡献，因此它对于识别新的药物靶点特别有用。提出的方法的另一个好处是，为这些研究开发的动态钳位技术可能被证明对治疗性的、反馈控制的大脑电刺激有用。 公共卫生相关性：拟议的项目与公共卫生相关，原因有两个。首先，这项拟议的工作允许对已知对认知、学习和记忆重要的有节奏的大脑活动进行严格研究。其次，为该项目开发和使用的电子技术将对神经科患者的基于反馈的脑结构电刺激具有价值。

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. PUBLIC HEALTH RELEVANCE: The proposed project is relevant to public health for two reasons. First, the proposed work allows rigorous study of rhythmic brain activity known to be important for cognition and learning and memory. Second, electronic technology being developed and used for this project will be valuable for feedback-based electrical stimulation of brain structures in neurological patients.