Continuous and Longitudinal Monitoring of Cerebral Blood Flow and Metabolism in Freely Moving Rodents

摘要 脑血流量(CBF)和脑耗氧代谢率(CMRO2)的测定 对大脑活动的反应允许研究潜在的兴奋性和抑制性神经反应和保持 优化神经疾病和脑血管疾病新疗法的关键。啮齿动物(小鼠 和老鼠)帮助科学家研究人类疾病已有一个多世纪的历史，至今仍占95% 今天使用的动物模型。这些啮齿动物模型的主要局限性是脑血流动力学 主要在麻醉动物身上测量，并在有限的时间点进行测量。然而，麻醉会影响大脑 血液动力学影响深远，并干扰对行为健康、认知功能和睡眠障碍的研究。 几种可用于清醒啮齿动物脑血流动力学监测的方法需要有创开颅手术 通过在大脑上安装各种光学电极/超声波探头，抑制动物的头部或 身体在测量过程中。在NIH(R21)的支持下，我们最近开发了一种创新的、非侵入性的、 低成本、无纤维、近红外漫反射散斑对比流量计(DSCF)探头，固定在头部 对麻醉的啮齿动物和清醒的人类进行脑血流量的持续监测。这项提议的目标是 将这项新技术扩展、优化并验证为双波长、多通道、漫反射散斑 对比流-血氧仪(DSCFO)系统用于同时进行CBF、脑氧合和 清醒、自由活动的啮齿动物体内的CMRO2。DSCFO在不同的位置使用小型近红外激光二极管 作为点源的波长和作为2D探测器阵列的微型CMOS摄像机来检测空间动态光 红细胞本征运动的散射(即CBF)和氧合和脱氧血红蛋白的光衰减 吸光度([HBO2]和[Hb])。CBF、[HBO2]和[Hb]的组合使CMRO2的推导基于 已建立的模型。2D摄像机阵列能够对两个半球的大脑反应进行2D映射 在啮齿动物头部的不同深度。重要的是，DSCFO探头和控制单元之间的连接 都是电线/电缆(即，无光纤)，从而为在 自由移动的对象。在使用模拟头部模型对DSCFO系统进行校准和优化后， 在麻醉啮齿动物身上的验证，我们将评估其性能 有或无脑缺血的清醒、自由活动啮齿动物的连续和纵向脑监测 中风侮辱。当我们在这个项目中探索中风导致的大脑结果时，DSCFO技术是 适用于其他神经系统疾病和脑血管疾病的研究。与我们的 正在进行的人类R21研究，在啮齿动物身上完成这项研究将产生一种独特的非侵入性， 用于神经科学研究和临床的快速、低成本、多尺度和多模式的脑成像工具 申请。最终，CBF、[HBO2]、[Hb]和CMRO2的水平/变化和组合可能作为 用于评估大脑健康和脑病理状况和干预结果的生物标记物。

ABSTRACT Measurements of cerebral blood flow (CBF) and cerebral metabolic rate of oxygen consumption (CMRO2) in response to brain activity allows investigation of underlying excitatory and inhibitory neural responses and holds the key to optimizing novel therapies for neurological disorders and cerebrovascular diseases. Rodents (mice and rats) have been helping scientists investigate human diseases for well over a century and still make up 95% of the animal models used today. Major limitations with these rodent models are that cerebral hemodynamics is measured mostly in anesthetized animals and at limited time points. However, anesthesia impacts cerebral hemodynamics profoundly and interferes with studies of behavioral health, cognitive function, and sleep disorder. A few methods available for cerebral hemodynamic monitoring in conscious rodents require invasive craniotomy with installation of various opto-electrode/ultrasound probes onto the brain, which restrains animal’s head or body during measurements. Supported by NIH (R21), we have recently developed an innovative, noninvasive, low-cost, fiber-free, near-infrared diffuse speckle contrast flowmetry (DSCF) probe, which affixes on the heads of anesthetized rodents and awake humans for continuous monitoring of CBF. The goal of this proposal is to extend, optimize, and validate this novel technology toward a dual-wavelength, multi-channel, diffuse speckle contrast flow-oximetry (DSCFO) system for simultaneous regional mapping of CBF, cerebral oxygenation, and CMRO2 in conscious, freely moving rodents. DSCFO uses small near-infrared laser diodes at different wavelengths as point sources and a tiny CMOS camera as a 2D detector array to detect spatial dynamic light scattering by intrinsic motions of red blood cells (i.e., CBF) and light attenuations by oxy- and deoxy- hemoglobin absorptions ([HbO2] and [Hb]). Combination of CBF, [HbO2], and [Hb] enables derivation of CMRO2 based on established models. The 2D camera array enables 2D mapping of cerebral responses over two hemispheres and at different depths of the rodent head. Importantly, connections between the DSCFO probe and control unit are all electrical wires/cables (i.e., fiber-free), thereby offering the promise for continuous cerebral monitoring in freely moving subjects. After calibrating and optimizing the DSCFO system using head-simulating phantoms and validation in anesthetized rodents against established techniques, we will evaluate its performance for continuous and longitudinal cerebral monitoring in conscious, freely moving rodents with or without ischemic stroke insult. While we explore stroke-induced cerebral outcomes in this project, the DSCFO technology is applicable for studying other neurological disorders and cerebrovascular diseases. In combination with our ongoing R21 studies in human subjects, completion of this study in rodents will generate a unique noninvasive, fast, low-cost, multiscale, and multimodal brain mapping tool for both neuroscience research and clinical applications. Ultimately, the levels/variations and combination of CBF, [HbO2], [Hb], and CMRO2 may serve as biomarkers for assessing brain health and outcomes of cerebral pathological conditions and interventions.