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，大量的气味感受器，以及缺乏任何关于气味性质的清晰映射，对嗅觉的理解被证明是极其困难的。因此，确定嗅觉系统中神经回路和基本计算的基础研究对阐明嗅觉原理至关重要。在嗅球中，感觉信息包含在二尖瓣细胞活动的精确时空模式中，二尖瓣细胞是嗅球的主要神经元。这些气味特定的模式是分两个阶段产生的。首先，每个二尖瓣细胞在称为小球的单一输入结构上接受感觉输入。气味会激活特定但重叠的肾小球，导致二尖瓣细胞输入的模式难以区分。第二，局部抑制颗粒细胞介导二尖瓣细胞之间的侧向抑制，并随时间解除二尖瓣细胞活动的相关性。因此，二尖瓣细胞-颗粒细胞的相互作用增加了二尖瓣细胞活动模式在不同气味之间的区分性。因此，颗粒细胞的功能性募集是嗅觉的关键步骤，但有关颗粒细胞募集的多个基本问题仍然存在。首先，肾小球组织在颗粒细胞募集中的作用是什么？解剖学数据表明，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。第二，二尖瓣细胞活动的时间顺序如何影响颗粒细胞的募集？颗粒细胞募集的缓慢但输入特异的动力学表明，同步的二尖瓣细胞活动可能不是功能性募集颗粒细胞的最佳选择。因此，拟议研究的主要目标是调查控制颗粒细胞募集的空间和时间特性。拟议研究的目的1是测试空间肾小球组织是否控制颗粒细胞的招募。对颗粒细胞的前馈输入将使用电压钳记录和细胞外和光遗传肾小球刺激进行比较，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同一肾小球的二尖瓣细胞，将使用成对电压钳记录比较连接到同一肾小球的二尖瓣细胞和连接到不同肾小球的二尖瓣细胞之间的横向抑制。拟议研究的目标2是确定二尖瓣细胞活动的时间序列如何调节颗粒细胞的招募。颗粒的时间调谐 首先将使用钙成像来测量细胞募集，以监测大颗粒细胞群的募集，同时以不同的时间偏移量刺激邻近的肾小球。二尖瓣细胞同步性对颗粒细胞募集的影响将通过配对的二尖瓣细胞记录结合钙成像来直接检测。总而言之，拟议的研究将为嗅球回路的一个关键方面提供新的见解：支配颗粒细胞招募的空间和时间特性。

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.