Amino acid neurotransmitter sensors for MRI

描述(申请人提供)：使用新的测量方法可以显著加快对正常大脑功能和疾病所涉及的神经机制的分析，这种方法以分子特异性、非侵入性和跨整个大脑报告神经处理事件。在这里，我们建议开发一个分子传感器平台，通过无创磁共振成像(MRI)对谷氨酸和伽马氨基丁酸(GABA)这两种最重要的氨基酸神经递质进行成像。传感器将通过修饰一系列氨基酸结合蛋白来形成，这些蛋白带有Gd的螯合基团。由此产生的探测器将在整个大脑区域或完整大脑的范围内，实现与行为相关的时间分辨率的“神经化学成像”。这一全新的能力将使我们和其他人能够回答有关脊椎动物中枢神经系统中主要的兴奋性和抑制性神经递质如何参与大脑生理的多个方面的具体问题。我们的传感器设计是基于在所谓的捕蝇器结构域(VFD)中诱导的大的配体依赖的结构变化。通过在策略性选择的氨基酸位置上将含Gd的基团与VFD偶联，我们希望产生对自然结合到每个相应的VFD的配体具有敏感性的MRI造影剂。在目标1中，我们将使用这一策略从细菌周质结合蛋白YbeJ中制备基于VFD的谷氨酸敏感磁共振造影剂。在这一目标的初步工作中，我们已经观察到由于谷氨酸与Gd衍生的YbeJ变体结合而导致的巨大MRI变化，表明我们方法的总体前景。在目标2中，我们将在大鼠大脑中应用我们的谷氨酸传感器，并使用它们来绘制具有代表性的体感刺激期间谷氨酸的释放模式。我们还将比较谷氨酸和常规功能磁共振(FMRI)激活图，以检验血流动力学fMRI测量密切反映谷氨酸能信号的假设。我们最近使用一种不太有效的MRI传感器在大鼠大脑中检测到多巴胺释放，这代表了拟议的活体工作的先例，并再次表明了前景。在目标3中，我们将把我们的谷氨酸传感器设计策略扩展到针对大脑中主要的抑制性神经递质GABA。拟议中的研究已经

DESCRIPTION (provided by applicant): Analysis of neural mechanisms involved in normal brain function and disease could be dramatically accelerated using novel measurement methods that report neural processing events with molecular specificity, noninvasively, and across the entire brain. Here we propose to develop a molecular sensor platform for imaging the two most important amino acid neurotransmitters, glutamate and gamma-aminobutyric acid (GABA), by noninvasive magnetic resonance imaging (MRI). Sensors will be formed by modifying a family of amino acid binding proteins with gadolinium chelating groups. The resulting probes will enable "neurochemical imaging" with behaviorally-relevant temporal resolution, on the scale of entire brain regions or intact brains. This qualitatively new capabilit will enable us and others to answer specific questions about how the dominant excitatory and inhibitory neurotransmitters in the vertebrate central nervous system participate in multiple facets of brain physiology. Our sensor design is based on the large ligand-dependent structural changes induced in so-called venus flytrap domains (VFDs). By conjugating gadolinium-containing groups to VFDs at strategically chosen amino acid positions, we expect to generate MRI contrast agents with sensitivity to the ligands that naturally bind to each corresponding VFD. In Aim 1, we will use this strategy to generate glutamate-sensitive MRI contrast agents based on VFDs from the bacterial periplasmic binding protein YbeJ. In preliminary work on this Aim, we have already observed large MRI changes due to glutamate binding to gadolinium-derivatized YbeJ variants, indicating the overall promise of our approach. In Aim 2, we will apply our glutamate sensors in rat brains and use them to map glutamate release patterns during a representative somatosensory stimulus. We will also compare glutamate and conventional functional MRI (fMRI) activation maps to examine the hypothesis that hemodynamic fMRI measures closely reflect glutamatergic signaling. Our recent detection of dopamine release using a less potent form of MRI sensor in rat brains represents a precedent for the proposed in vivo work, and again indicates promise. In Aim 3, we will extend our glutamate sensor design strategy to target GABA, the dominant inhibitory neurotransmitter in the brain. The proposed research has