Genetically-targeted hemodynamic functional imaging

人类和不透明哺乳动物脑功能成像的主要技术是利用he- 由神经活动和血流变化之间的耦合产生的动力学对比， 通过非侵入性成像方法检测，包括功能性磁共振成像（fMRI）、功能性 光声断层扫描（fPAT）、功能超声成像（fUS）等。虽然血流动力学 人类和动物的功能成像已经被用来做出一些最重要的发现- 在神经科学中，这些技术由于缺乏对机械上不同的成分的特异性而受到限制， 大脑活动的神经元。我们的团队帮助领导了绕过血流动力学功能图像限制的努力， 通过开发分子探针，通过非侵入性神经活动报告生理特异性标志， 动态成像在此，我们提出了一项补充性的、前所未有的战略，即“在 系统”，以提高特异性内在血流动力学读数本身。具体来说，我们建议- 在神经上增强直接将靶向神经元或神经胶质的活性与血管结合的信号通路， sels，从而引入可归因于不同细胞类型的人工血液动力学功能信号-或 大脑中特定回路的细胞过程。这种方法将利用由血红素提供的放大作用， 动态成像，同时绕过内源性神经血管机制的许多复杂性， 劫持血液动力学信号来报告电路或细胞类型特定的活动。与基于 在更传统的成像方法，工程血流动力学成像方法将提供关键的广告， 优点：（1）对基因靶向脑回路和细胞类型进行选择性成像的能力，（2）兼容性， 与各种遗传工具，特别是包括病毒转导和追踪载体，（3）适用于 在多个物种中的全脑深部组织成像，（4）与许多已建立的功能模式的兼容性， （5）对相对低的活动水平和稀疏的神经元群体的潜在敏感性。 我们在这一新战略上的工作将分为两个目标：在目标1中，我们将设计一个新的家庭， 基因编码的神经活动报告者将成为新的工程血流动力学成像的基础， approach.报告基因将来源于天然存在的一氧化氮合酶， 被称为NOSTIC。在目标2中，我们将使用病毒载体将NOSTIC基因递送到大鼠脑中，并进行一个 广泛的一系列成像和组织学研究，以验证和优化我们的新成像在体内。 我们预计，这些目标的完成将为多模态成像引入一种有效的新方法- 基于电路和细胞类型对不同物种神经功能的特定贡献的研究， 行为背景

The dominant techniques for brain-wide functional imaging in humans and opaque mammals make use of he- modynamic contrast that results from coupling between neural activity and changes in blood flow and can be detected by noninvasive imaging methods including functional magnetic resonance imaging (fMRI), functional photoacoustic tomography (fPAT), functional ultrasound imaging (fUS), and others. Although hemodynamic functional imaging in both humans and animals has been used to make some of the most important discover- ies in neuroscience, the techniques are limited by their lack of specificity to mechanistically-distinct compo- nents of brain activity. Our group has helped lead efforts to bypass limitations of hemodynamic functional imag- ing by developing molecular probes that report physiologically-specific hallmarks of neural activity via noninva- sive imaging. Here we propose the complementary and hitherto unprecedented strategy of working “within the system” to improve the specificity intrinsic hemodynamic readouts themselves. Specifically, we propose to ge- netically enhance a signaling pathway that directly couples the activity of targeted neurons or glia to blood ves- sels, thus introducing artificial hemodynamic functional signals that can be attributed to distinct cell type- or circuit-specific cellular processes in the brain. This approach will harness the amplification afforded by hemo- dynamic imaging while bypassing numerous complexities of endogenous neurovascular mechanisms, in effect hijacking hemodynamic signals to report on circuit- or cell type-specific activity. Compared with efforts based on more conventional imaging methods, the engineered hemodynamic imaging approach will offer key ad- vantages: (1) capability for selective imaging of genetically-targeted brain circuits and cell types, (2) compatibil- ity with a variety of genetic tools, in particular including viral transduction and tracing vectors, (3) applicability to brain-wide deep tissue imaging in multiple species, (4) compatibility with many established modalities for func- tional neuroimaging, (5) potential sensitivity to relatively low activity levels and sparse neuronal populations. Our work on this novel strategy will be organized into two Aims: In Aim 1 we will engineer a new family of genetically encodable neural activity reporters that will underlie the new engineered hemodynamic imaging approach. The reporters will be derived from naturally occurring nitric oxide synthase enzymes and are re- ferred to as NOSTICs. In Aim 2, we will deliver NOSTIC genes to rat brains using viral vectors, and perform an extensive series of imaging and histological investigations to validate and optimize our new imaging in vivo. We anticipate that completion of these Aims will introduce a potent new approach for multimodal imaging- based investigations of circuitry and cell type-specific contributions to neural function in diverse species and behavioral contexts.