Nanosensors for sensitive brain-wide neurochemical imaging

神经回路的大规模动力学依赖于许多神经化学物质之间的相互作用， 这些细胞在整个大脑中发挥着不同的功能。了解空间和时间特征- 因此，化学信号的物理学对于建立大脑功能的机械模型至关重要。本实验室 介绍了顺磁神经递质传感器，使神经化学现象的功能分析 通过分子水平的功能性磁共振成像（molecularfunctionalmagneticresonanceimaging，molecularfMRI）在大视场上进行观察。我们有 这些传感器在一系列神经化学现象的时空映射中的公开应用， 大量的文件。然而，这种实验的范围受到所提供的适度灵敏度的限制。 通过现有的探针，其必须以大大超过生理神经的浓度施加， 发射器水平。该提案的目标是建立一个平台技术， 以高得多的灵敏度成像，最初集中在单胺递质上。我们的做法是根据 在MRI中使用顺磁性脂质体作为响应对比的生物化学传感的新原理 剂.在这种机制中，神经递质靶点的存在门控由神经递质靶点提供的大对比度效应。 脂质体，相对于以前的探针产生强大的放大因子。通过这种设计，我们 预测对行为相关的低微摩尔或亚微摩尔神经递质浓度的敏感性 将以最小的潜在缓冲效应实现。此外，我们的初步研究表明， 用这些探针进行宽视野脑递送是可以实现的，我们还预测突触周细胞类型特异性 可以通过靶向脂质体获得读数。 我们的工作将解决三个目标：在目标1，我们将建立我们的脂质体为基础的纳米传感器（LBN）平台， 通过结合脂质、多肽和小分子成分形成，以建立新的传感机制 我们试图利用。我们将使用各种合成和分子工程方法来优化这种机制- 用于检测行为相关的间质多巴胺和5-羟色胺浓度，目的是 实现0.1-1 µM范围内的灵敏度。在目标2中，我们将优化策略，在全脑范围内提供这些 探针，利用化学介导的血脑屏障破坏和注入脑脊液。我们 也将实施突触周围定位方法。在目标3中，我们将验证基于脂质体的多巴胺， 大鼠活体脑中5-羟色胺LBN的分子功能磁共振成像，参照平行的神经化学和血流动力学 fMRI测量。除了建立我们提出的新的神经化学成像平台外， 实验将首次获得多巴胺和血清素信号的广域分布数据 以及这些神经化学物质与传统大脑活动读数的关系。 虽然我们将开发的技术最初将应用于镇静的啮齿动物，但我们预计它将适用于 许多其他的物种和行为环境。

The large-scale dynamics of neural circuitry depend on interactions among numerous neurochemical spe- cies that play functionally distinct roles throughout the brain. Understanding the spatial and temporal character- istics of chemical signaling is thus crucial for building mechanistic models of brain function. Our laboratory has introduced paramagnetic neurotransmitter sensors that enable functional analysis of neurochemical phenomena over large fields of view by molecular-level functional magnetic resonance imaging (molecular fMRI). We have published applications of these sensors to spatiotemporal mapping of neurochemical phenomena in a series of substantial papers. The scope of such experiments has however been limited by the modest sensitivity provided by the existing probes, which must be applied at concentrations that substantially exceed physiological neuro- transmitter levels. The goal of this proposal is to establish a platform technology for noninvasive neurochemical imaging with substantially higher sensitivity, focusing initially on monoamine transmitters. Our approach is based on a novel principle for biochemical sensing in MRI that uses paramagnetic liposomes as responsive contrast agents. In this mechanism, the presence of neurotransmitter targets gates large contrast effects afforded by the liposomes, giving rise to a formidable amplification factor with respect to previous probes. Using this design, we predict that sensitivity to behaviorally relevant low-micromolar or submicromolar neurotransmitter concentrations will be achieved, with minimal potential for buffering effects. In addition, our preliminary studies suggest that wide-field brain delivery with these probes is achievable, and we also predict that perisynaptic cell type-specific readouts can be obtained by targeting the liposomes. Our work will address three Aims: In Aim 1, we will establish our liposome-based nanosensor (LBN) plat- form by combining lipid, polypeptide, and small molecular components to establish the new sensing mechanism we seek to exploit. We will use a variety of synthetic and molecular engineering methods to optimize this mech- anism for detection of behaviorally relevant interstitial dopamine and serotonin concentrations, with the goal of achieving sensitivity in the 0.1-1 µM range. In Aim 2, we will optimize strategies for brain-wide delivery of these probes, exploiting chemically-mediated blood-brain barrier disruption and infusion into cerebrospinal fluid. We will also implement a perisynaptic targeting approach. In Aim 3, we will validate liposome-based dopamine and serotonin LBNs by molecular fMRI in live rat brains, with reference to parallel neurochemical and hemodynamic fMRI measurements. In addition to establishing the novel neurochemical imaging platform we propose, these experiments will yield first-of-their-kind data about the wide-field distribution of dopamine and serotonin signaling in response to stimuli, as well as the relationship of these neurochemicals to conventional brain activity readouts. Although the technology we will develop will initially be applied in sedated rodents, we expect it to be applicable to many additional species and behavioral contexts.