SPATIAL AND TEMPORAL PROPERTIES OF GRANULE CELL RECRUITMENT IN THE MAMMALIAN OLFA

描述（申请人提供）：嗅觉系统对气味的编码对哺乳动物的交流和生存至关重要。然而，由于气味的巨大多样性、大量的气味受体以及缺乏任何气味质量的清晰映射，理解嗅觉已被证明是极其困难的。因此，识别嗅觉系统中神经回路和基本计算的基础研究对于阐明嗅觉原理至关重要。在嗅球中，感觉信息包含在嗅球主要神经元二尖瓣细胞活动的精确时空模式中。这些特定气味的模式是在两个阶段产生的。首先，每个二尖瓣细胞在一个叫做肾小球的单一输入结构中接受感觉输入。气味激活特定但重叠的肾小球，产生难以区分的二尖瓣细胞输入模式。其次，局部抑制颗粒细胞介导二尖瓣细胞和二尖瓣细胞活性间的横向抑制。二尖瓣细胞-颗粒细胞的相互作用因此增加了二尖瓣细胞活动模式在不同气味之间的可辨别性。因此，颗粒细胞的功能性募集是嗅觉的关键步骤，但关于颗粒细胞募集的许多基本问题仍然存在。首先，肾小球组织在颗粒细胞募集中的作用是什么？解剖数据表明颗粒细胞优先连接连接到同一肾小球的二尖瓣细胞，但这种空间偏好仍有待功能证实。其次，二尖瓣细胞活性的时间序列如何影响颗粒细胞募集？颗粒细胞招募的缓慢但输入特异性动力学表明，同步二尖瓣细胞活性可能不是功能招募颗粒细胞的最佳选择。因此，提出的研究的主要目的是研究控制颗粒细胞募集的空间和时间特性。本研究的目的1是测试空间肾小球组织是否控制颗粒细胞募集。通过电压钳记录、细胞外和光遗传学肾小球刺激，对颗粒细胞的前馈输入进行比较，假设在刺激特定肾小球时输入最强。为了测试颗粒细胞是否优先连接连接到相同肾小球的二尖瓣细胞，颗粒细胞介导的侧抑制将使用配对电压钳记录比较连接到相同肾小球的二尖瓣细胞和连接到不同肾小球的二尖瓣细胞。本研究的目的2是确定二尖瓣细胞活性的时间序列如何调节颗粒细胞募集。颗粒的时间调谐

DESCRIPTION (provided by applicant): The encoding of smell by the olfactory system is critical to mammalian communication and survival. Under- standing olfaction has proven extremely difficult, however, due to the vast diversity of odors, the large number of odor receptors, and the lack of any clear mapping of odor qualities. Fundamental research identifying the neural circuitry and basic computations performed in the olfactory system has thus been pivotal in elucidating principles of olfaction. In the olfactory bulb, sensory information is contained in precise spatiotemporal patterns of activity in mitral cells, the olfactory bulb princial neurons. These odor-specific patterns are generated in two stages. First, each mitral cell receives sensory input at a single input structure called a glomerulus. Odors activate specific but overlapping glomeruli, yielding poorly discriminable patterns of mitral cell input. Second, local inhibitory granule cells mediate lateral inhibition between mitral cells and decorrelate mitrl cell activity across time. Mitral cell-granule cell interactions thereby increase the discriminabilty of mitral cell activity patterns between different odors. Functional recruitment of granule cells i thus a critical step in olfaction, yet multiple fundamental questions remain concerning granule cell recruitment. First, what is the role of glomerular organization in granule cell recruitment? Anatomical data suggests that granule cells preferentially link mitral cells connected to the same glomerulus, but this spatial preference remains to be functionally confirmed. Second, how does the temporal sequence of mitral cell activity influence granule cell recruitment? The slow but input- specific kinetics of granule cell recruitment suggest that synchronous mitral cell activity may not be optimal for functionally recruiting granule cells. Thus, the primary objective of the proposed research is to investigate the spatial and temporal properties governing granule cell recruitment. Aim 1 of the proposed research is to test whether spatial glomerular organization controls granule cell recruitment. Feedforward input to granule cells will be compared across glomeruli using voltage-clamp recordings and extracellular and optogenetic glomerular stimulation, with the hypothesis that input will be strongest when stimulating a specific glomerulus. To test if granule cells preferentially link mitral cells connected to the same glomerulus, granule cell-mediated lateral inhibition will be compared between mitral cells connected to the same glomerulus and mitral cells connected to different glomeruli using paired voltage-clamp recordings. Aim 2 of the proposed research is to determine how the temporal sequence of mitral cell activity regulates granule cell recruitment. The temporal tuning of granule cell recruitment will first be measured using calcium imaging to monitor recruitment across large granule cell populations while stimulating neighboring glomeruli at varying temporal offsets. The influence of mitral cell syn- chrony on granule cell recruitment will then be directly examined using paired mitral cell recordings coupled with calcium imaging. Collectively, the proposed research will thus provide novel insight into a critical aspect of olfactory bulb circuitry: the sptial and temporal properties governing granule cell recruitment.