Neuronal, glial and BOLD fMRI signals: From BOLD to 2-photon microscopy

描述(申请人提供)：功能磁共振成像(FMRI)已成为人类功能神经成像研究的一种选择方法，并开始进入临床应用，如监测中风康复。然而，在目前的实践中，fMRI成像的血流动力学响应与潜在的神经胶质细胞活动和定量血流动力学参数之间的关系不确定。在疾病状态下对fMRI研究的解释更加含糊，因为它不仅需要了解神经血管耦合的机制，而且需要了解在神经血管缺陷的情况下，脑血管动力学改变对BOLD信号的影响。因此，到目前为止，对功能磁共振数据的分析在很大程度上是相关和描述性的。为了从机制上理解大胆对比度和潜在的神经胶质细胞活动之间的关系，人们必须考虑从宏观血流动力学变化到微观神经血管沟通的多个生理过程。为此，我们将结合血流动力学和神经元参数的直接和定量测量与功能磁共振成像，旨在了解BOLD反应和潜在的神经胶质细胞活动之间的关系。然后，我们将建立大规模(人口)血流动力学和神经胶质信号的微观关联，并将宏观和微观测量相结合。具体地说，在Aim1中，我们将通过同时使用血氧和血流的光学成像来表征血流动力学方面的BOLD信号。在AIM2中，我们将通过同时进行钙成像(使用荧光钙指示剂)和电压敏感染料成像来建立刺激诱导的BOLD反应与潜在的神经元和星形胶质细胞活动之间的相关性。我们选择钙作为神经胶质细胞活性的指标是基于它在多个分子信号转导途径中作为重要的第二信使的公认作用，包括那些与神经血管通讯密切相关的分子信号转导途径。最后，我们将使用双光子显微镜建立大规模血流动力学和钙信号的微观关联(目标3)。将宏观功能磁共振成像和钙测量与双光子数据相结合，将允许根据潜在的单细胞和单血管的活动对BOLD信号进行机械解释。公共卫生相关性：功能磁共振成像(FMRI)信号和潜在的显微神经血管单位(NVU)生理学之间的关系是解释人类功能神经成像数据的一个中心悬而未决的问题。这项建议的主要目标是将血流动力学和神经胶质信号的定量光学测量直接与BOLD功能磁共振相结合，旨在根据潜在的单个细胞和单个血管的活动来机械地解释BOLD信号。拟议的项目将为理解功能磁共振信号提供一个机械框架，并最终将指导新的治疗、预防和诊断方法的发展。

DESCRIPTION (provided by applicant): Functional Magnetic Resonance Imaging (fMRI) has become a method of choice for human functional neuroimaging studies, and is beginning to make inroads into clinical applications such as monitoring of stroke rehabilitation. However, in current practice, fMRI suffers from the uncertain relation of the imaged hemodynamic responses to the underlying neuroglial activity and quantitative hemodynamic parameters. Interpretation of fMRI studies in disease states are even more ambiguous since it requires not only understanding the mechanisms of neurovascular coupling but the impact of altered cerebrovascular dynamics on the BOLD signal under conditions of neurovascular deficit. As a result, the analysis of fMRI data has so far been largely correlational and descriptive. In order to gain a mechanistic understanding of the relationship between BOLD contrast and the underlying neuroglial activity, one has to consider multiple physiological processes, from macroscopic hemodynamic changes to the microscopic neurovascular communication. To this end, we will combine direct and quantitative measurement of hemodynamic and neuronal parameters simultaneously with fMRI aiming to understand the relationship between the BOLD response and the underlying neuroglial activity. We then will establish microscopic correlates of large-scale (populational) hemodynamic and neuroglial signals and will integrate macro- and microscopic measurements. Specifically, in Aim1 we will characterize BOLD signals in hemodynamic terms by employing simultaneous optical imaging of blood oxygenation and blood flow. In Aim2 we will establish a correlation between stimulus-induced BOLD response and the underlying neuronal and astrocytic activity by performing simultaneous calcium imaging (using fluorescent calcium indicators) and voltage-sensitive dyes imaging. Our choice of calcium as an indicator of neuroglial activity is based on its recognized role as an important second messenger in multiple molecular signal transduction pathways, including those intimately involved in neurovascular communication. Finally, we will establish microscopic correlates of the large-scale hemodynamic and calcium signals by using 2-photon microscopy (Aim 3). Integration of macroscopic fMRI and calcium measurements with 2-photon data will allow a mechanistic interpretation of BOLD signals in terms of activity of underlying single cells and single blood vessels. PUBLIC HEALTH RELEVANCE: The relationship between functional MRI (fMRI) signals and the underlying microscopic neurovascular unit (NVU) physiology is a central unresolved issue in the interpretation of human functional neuroimaging data. The main goal of this proposal is to combine quantitative optical measurements of hemodynamic and neuroglial signals directly with BOLD fMRI aiming for a mechanistic interpretation of BOLD signals in terms of activity of the underlying single cells and single blood vessels. The proposed project will provide a mechanistic framework for understanding of fMRI signals and ultimately will guide the development of novel therapeutic, preventative, and diagnostic approaches.