INHIBITORY SYNAPTIC MECHANISMS UNDERLYING VISUAL CORTICAL PROCESSING

描述：（由申请人提供）：感觉皮质神经元的功能特性，反映在它们对刺激属性的反应选择性上，主要是由感觉诱发的兴奋性和抑制性突触输入的时空整合决定的。该项目的目的是提供皮层细胞功能特性背后的兴奋性和抑制性突触机制的理解。突触抑制在形成视觉皮层加工过程中的作用仍然存在争议。此外，由于难以在体内识别和靶向皮质抑制性神经元，这些神经元的感受野（RF）特性在很大程度上仍然难以捉摸，而这些神经元对突触抑制功能至关重要。我们建议结合体内全细胞记录和双光子成像技术，并利用小鼠遗传模型来确定视觉皮质神经元兴奋性和抑制性输入的响应特性。在Aim 1中，我们将使用“盲”全细胞电压钳记录结合组织学，解剖稀疏闪光刺激引起的皮质兴奋性神经元的兴奋性和抑制性突触传导。我们将确定简单和复杂的感受野结构是如何由突触输入的空间分布决定的。通过重构由这些突触输入引起的膜电位变化，我们将验证抑制输入在锐化spike On和Off感受野的空间离散性中起关键作用的假设。在Aim 2中，我们将在转基因小鼠系中进行双光子成像引导的松散补丁记录，其中抑制神经元用绿色荧光蛋白标记。我们将研究荧光抑制性神经元和非荧光兴奋性神经元的视觉诱发峰反应，并验证这两组神经元之间存在功能差异的假设，即抑制性神经元对空间相位和方向等刺激属性的选择性较低。在Aim 3中，通过应用成像引导的全细胞电流钳和电压钳记录，我们将验证兴奋性和抑制性神经元之间的功能差异可以归因于它们接收的突触输入强度的差异，而不是突触输入电路结构的差异。这些研究将为功能性皮层回路提供新的见解。在中枢神经系统中，抑制性突触输入控制网络活动的增益，并在信息处理中发挥关键作用。突触抑制异常与几种认知障碍和与年龄相关的知觉功能下降有关。该项目将促进我们对抑制回路在视觉处理中的作用的理解，并可能为抑制神经元的功能变化如何导致认知功能的恶化提供重要的见解。

Description: (provided by applicant): The functional properties of sensory cortical neurons, as reflected in their response selectivity to stimulus attributes, are primarily determined by the spatiotemporal integration of sensory-evoked excitatory and inhibitory synaptic inputs to the cell. The objective of this project is to provide an understanding of excitatory and inhibitory synaptic mechanisms underlying the cortical cells' functional properties. The role of synaptic inhibition in shaping visual cortical processing has remained controversial. In addition, due to the difficulties in identifying and targeting cortical inhibitory neurons in vivo, the receptive field (RF) properties of these neurons, which are crucial to the function of synaptic inhibition, remain largely elusive. We propose to combine the in vivo whole-cell recording and two-photon imaging techniques, and exploit mouse genetic models, to determine the response properties of excitatory and inhibitory inputs in visual cortical neurons. In Aim 1, using "blind" whole-cell voltage-clamp recording coupled with histology, we will dissect the excitatory and inhibitory synaptic conductances of cortical excitatory neurons evoked by sparse flash stimuli. We will determine how simple and complex receptive field structures are determined by the spatial distribution of synaptic inputs. By reconstituting the membrane potential changes that result from these synaptic inputs, we will test the hypothesis that inhibitory inputs play a crucial role in sharpening the spatial discreteness of spike On and Off receptive fields. In Aim 2, we will perform two-photon imaging guided loose patch recording in a transgenic mouse line where inhibitory neurons are labeled with green fluorescence protein. We will examine visually evoked spike responses of both fluorescent inhibitory neurons and non-fluorescent excitatory neurons, and test the hypothesis that there are functional differences between these two groups of neurons, i.e. inhibitory neurons are less selective to stimulus attributes such as spatial phase and orientation. In Aim 3, by applying imaging guided whole-cell current-clamp and voltage-clamp recordings, we will test the hypothesis that the functional differences between excitatory and inhibitory neurons can be attributed to the difference in the strength of synaptic inputs they receive, rather than in the structure of synaptic input circuitry. These studies will provide novel insights into functional cortical circuitry. PUBLIC HEALTH RELEVANCE In the central nervous system inhibitory synaptic inputs control the gain of network activity and play a critical role in information processing. Abnormality in synaptic inhibition has been implicated in several cognitive disorders and age-related reduction in perceptual functions. The proposed project will advance our understanding of the role of inhibitory circuits in visual processing, and may provide important insights into how functional changes of inhibitory neurons can lead to deterioration of cognitive functions.