Chronic imaging of odor-evoked activity in olfactory bulb circuits of awake mice

描述（由申请人提供）：嗅觉在我们的生活质量中起着重要作用。然而，嗅觉信息在大脑中的处理和表征机制还没有得到很好的理解。在哺乳动物中，嗅球是负责嗅觉信息初始处理的关键大脑区域。我们目前对嗅球功能的理解大多是基于以前使用体外脑切片或麻醉动物急性制剂的研究。虽然这些方法提供了有价值的见解，但对清醒行为动物的气味编码知之甚少。例如，在长时间尺度上（即几天、几周、几个月），同一动物的气味表征的动态是什么？在清醒的、有行为的动物中，嗅球中的气味编码是如何通过经验和学习形成的？ 为了解决这些问题，我们提出了一个实验策略，使用慢性双光子钙成像研究清醒小鼠嗅球的气味诱发活动。具体目标1提出了一种方法的开发，用于选择性表达的遗传编码的钙指示剂GCaMP 3在主（二尖瓣/簇状）细胞或本地interneurons使用Cre依赖性，腺相关病毒系统。我们假设，这种方法将提供单细胞分辨率的动作电位依赖性钙信号在大规模的神经合奏，可以长期在清醒的，头部固定的小鼠成像。具体目标2提出了成像实验，以确定如何气味诱发反应的二尖瓣细胞和中间神经元（颗粒细胞）之间的不同清醒和麻醉状态。我们还将在清醒的动物中使用慢性成像，以确定在重复测试的数天内，神经集合中的气味诱发活动模式是稳定的还是动态的。这些实验将为清醒大脑中气味编码的本质提供新的见解。

DESCRIPTION (provided by applicant): The sense of smell plays an important role in our quality of life. However, the mechanisms governing the processing and representation of olfactory information in the brain are not well understood. In mammals, the olfactory bulb is a critical brain region responsible for the initial processing of olfactory information. Much of our current understanding of olfactory bulb function is based on previous studies using in vitro brain slices or acute preparations of anesthetized animals. While these approaches have provided valuable insight, much less is known about odor coding in awake, behaving animals. For example, what are the dynamics of odor representations in the same animal over long time scales (i.e. days, weeks, months) and how is odor coding in the olfactory bulb shaped by experience and learning in awake, behaving animals? To address these questions, we propose an experimental strategy using chronic 2-photon calcium imaging to study odor-evoked activity in the olfactory bulbs of awake mice. Specific Aim 1 proposes the development of an approach for the selective expression of the genetically-encoded calcium indicator GCaMP3 in principal (mitral/tufted) cells or local interneurons using a Cre-dependent, adeno-associated virus system. We hypothesize that this approach will provide single cell resolution of action potential-dependent calcium signals in large populations of neural ensembles that can be imaged chronically in awake, head fixed mice. Specific Aim 2 proposes imaging experiments to determine how odor-evoked responses of mitral cells and interneurons (granule cells) differ between the awake and anesthetized state. We will also use chronic imaging in awake animals to determine whether patterns of odor-evoked activity in neural ensembles are stable or dynamic over days of repeated testing. These experiments will provide new insight into the nature of odor coding in the awake brain.