Nanosensors for sensitive brain-wide neurochemical imaging

神经回路的大规模动力学依赖于众多神经化学空间之间的相互作用。 在整个大脑中扮演着不同功能角色的CIE。理解时空特征-- 因此，化学信号的特性对于建立大脑功能的机械模型至关重要。我们的实验室有 引入顺磁性神经递质传感器，使神经化学现象的功能分析成为可能 通过分子水平的功能磁共振成像(分子功能磁共振成像)获得更大的视野。我们有 已发表的这些传感器在一系列神经化学现象的时空映射中的应用 大量的文件。然而，这种实验的范围受到提供的适度敏感性的限制。 通过现有的探针，这些探针的应用浓度必须大大超过生理神经- 发射机电平。这项提案的目标是为非侵入性神经化学物质建立一个平台技术 成像灵敏度大大提高，最初集中在单胺发射器上。我们的方法是基于 利用顺磁性脂质体作为响应对比剂的磁共振生物化学传感新原理 探员们。在这一机制中，神经递质靶点的存在会产生强烈的对比度效应 脂质体，与以前的探针相比，产生了强大的放大系数。使用这种设计，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 将以最小的缓冲效果潜在地实现。此外，我们的初步研究表明， 用这些探针进行大范围的脑传递是可以实现的，我们还预测突触周围细胞的类型特异性 可以通过靶向脂质体获得读数。 我们的工作将涉及三个目标：在目标1中，我们将建立基于脂质体的纳米传感器(LBN)平台。 形成通过结合脂质、多肽和小分子成分来建立新的传感机制 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一机械- 检测行为相关间质多巴胺和5-羟色胺浓度的原理，目的是 在0.1-1微米范围内实现灵敏度。在目标2中，我们将优化在全脑范围内实现这些目标的策略 探头，利用化学介导的血脑屏障破坏和脑脊液输注。我们 还将实施突触周围靶向方法。在目标3中，我们将验证基于脂质体的多巴胺和 活体大鼠脑内5-羟色胺LBN分子功能磁共振成像与平行神经化学和血流动力学的关系 功能磁共振成像测量。除了建立我们提出的新型神经化学成像平台外，这些 实验将首次获得有关多巴胺和5-羟色胺信号的广域分布的数据。 对刺激的反应，以及这些神经化学物质与常规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 许多其他物种和行为背景。

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.