Optogenetic studies of mouse olfaction

描述（由申请人提供）：神经回路的功能受到单个神经元及其连接的特性的限制。在许多感觉系统中，电路元件的反应随着物理位置的变化而系统地变化，从而导致刺激空间的地形表征。嗅觉系统中的感觉表征更难破译，部分原因是难以找到适当的度量来表征气味空间并对该空间进行密集采样。在探测和控制早期嗅觉回路中的单个电路元件方面的技术限制也减慢了进展。在这个提议中，我们的目标是开发新的方法，将极大地帮助解剖小鼠嗅觉系统中的功能神经回路。老鼠依靠嗅觉来寻找食物、选择配偶和躲避捕食者。在哺乳动物中，嗅觉感觉神经元将其轴突发送到嗅球（OB），嗅球在肾小球层有一个典型的物理输入布局。每个肾小球接收来自大量表达相同气味受体的嗅觉感觉神经元的会聚传入信号，因此OB表面的每个点都具有特定的化学反应谱。OB的主要神经元，二尖瓣细胞和簇状细胞（M/T），通常有一个初级树突，投射到一个肾小球。M/T细胞也接受来自肾小球和外丛状层的多种中间神经元的侧向gaba能输入，从而使它们能够从几个功能不同的肾小球中采集信息。OB中的气味处理也受到来自皮层和脑干神经调节中心的反馈的强烈调节。在此，我们建议开发新的试剂和方法，以加快哺乳动物嗅觉研究的步伐。我们的实验将以三个具体目标为指导。目的1：产生在嗅觉感觉神经元中特异性表达光激活离子通道通道视紫红质的转基因小鼠系，使嗅球（肾小球）的输入层具有光学兴奋性。目的2：通过体外切片制备和数字镜像装置技术，证明利用该小鼠模型研究OB及其下游靶区的功能连通性的可行性。目的3：验证在正常自由呼吸小鼠OB及其靶脑区构建神经元肾小球接受野的可行性。这里开发的工具将有助于提高我们对气味编码的理解。此外，由于嗅觉经常被用作研究高级大脑功能（如决策）的感官通道，我们的工具也将有更广泛的用途。最后，通过将这些“光嗅觉”小鼠与其他疾病小鼠模型杂交，我们可以催化对自闭症和阿尔茨海默病等脑部疾病的感觉功能障碍的研究。

DESCRIPTION (provided by applicant): The function of a neural circuit is constrained by the properties of individual neurons and their wiring. In many sensory systems, the responses of the circuit elements vary systematically with physical position, leading to a topographic representation of the stimulus space. Sensory representation in the olfactory system has been harder to decipher, in part due to the difficulty in finding appropriate metrics to characterize the odor space and in sampling this space densely. Progress has also been slowed by technological limitations in probing and controlling individual circuit elements in early olfactory circuits. In this proposal, we aim to develop new methods that will greatly aid the dissection of functional neural circuits in the olfactory system in mice. Mice rely on olfaction to find food, choose mates and avoid predators. In mammals, olfactory sensory neurons send their axons to the olfactory bulb (OB), where there is a characteristic physical layout of inputs in the glomerular layer. Each glomerulus receives convergent afferents from a large number of olfactory sensory neurons expressing the same odorant receptor, so each point on the surface of the OB has a specific chemical response spectrum. The principal neurons in the OB, the mitral and tufted (M/T) cells, typically have a single primary dendrite that projects to a single glomerulus. M/T cells also receive lateral GABAergic inputs from a variety of interneurons in the glomerular and external plexiform layers, thus allowing them to sample information from several functionally diverse glomeruli. Odor processing in the OB is also strongly modulated by feedback from the cortex as well as brainstem neuromodulatory centers. Here, we propose to develop new reagents and methods that will accelerate the pace of research into mammalian olfaction. Our experiments will be guided by three specific aims. Aim 1: To generate transgenic mouse lines that express the light-activated ion channel channelrhodopsin specifically in olfactory sensory neurons, rendering the input layer of the olfactory bulb (glomeruli) optically excitable. Aim 2: To demonstrate the feasibility of using this mouse model to study functional connectivity in the OB and its downstream target areas using in vitro slice preparation and digital mirror device technology. Aim 3: To demonstrate the feasibility of constructing glomerular receptive fields of neurons in the OB and its target brain areas in the intact, freely breathing mouse. Tools developed here will help advance our understanding of odor coding. In addition, since the olfaction is often used as a sensory gateway to study higher brain function such as decision making, our tools will also have broader use. Finally, by crossing these "opto-olfactory" mice with other mouse models of disease, we can catalyze studies of sensory dysfunction in brain disorders such as autism and Alzheimer's disease.