Investigation of the Modulators of Cerebrovascular Coupling

脑血管耦合调节剂的研究

• 批准号: 8557035
• 负责人: Afonso Silva
• 金额: $ 164.2万
• 依托单位: NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8557035
• 关键词: Acute; Address; Adopted; Afferent Pathways; Age; Architecture; Area; Arteries; Astrocytes; Benign; Blood; Blood Pressure; Blood Vessels; Blood capillaries; Brain; Brain Edema; Brain imaging; Caliber; Cells; Cerebral Ischemia; Cerebrovascular Circulation; Cerebrum; Chronic; Collateral Circulation; Complex; Cortical Column; Coupling; Data; Diffusion; Disease; Drainage procedure; Dyes; Edema; Electrophysiology (science); Energy Supply; Erythrocytes; Evolution; Excision; Functional Magnetic Resonance Imaging; Functional disorder; Future; Goals; Healthcare; Homeostasis; Hour; Human; Hyperemia; Hypertension; Image; Inbred SHR Rats; Inbred WKY Rats; Individual; Infarction; Interneurons; Investigation; Ischemia; Ischemic Brain Injury; Ischemic Penumbra; Ischemic Stroke; Label; Laser Scanning Microscopy; Lesion; Light; Magnetic Resonance Imaging; Manuscripts; Maps; Measurement; Measures; Mediating; Mediator of activation protein; Microscopy; Middle Cerebral Artery Occlusion; Modeling; Molecular; Neuroglia; Neurologic; Neurons; Organ; Outcome; PTGS2 gene; Pathway interactions; Patients; Penetration; Perfusion; Perfusion Weighted MRI; Phenylephrine; Photons; Physiological; Plasma; Predisposition; Price; Process; Publishing; Rattus; Regulation; Relative (related person); Reperfusion Therapy; Reporting; Research; Resistance; Resolution; Risk Factors; Role; Sensory; Severities; Shapes; Signal Pathway; Signal Transduction; Specificity; Staging; Stroke; Techniques; Time; Translating; Vascular blood supply; Veins; Weight; Work; acute stroke; base; brain research; capillary; cerebrovascular; feeding; hemodynamics; interest; ischemic lesion; millimeter; neurochemistry; neuroimaging; neurovascular unit; prevent; relating to nervous system; research study; response; restoration; soft tissue; two-photon; vasoactive agent; wasting

We are interested in establishing the physiological role of well-established neurochemical pathways (such as NO and COX-2) in shaping the spatial specificity of CBF regulation. The working hypothesis is that vasoactive substances released by strategically located cells in the parenchyma act on the cerebral vessels and regulate their tone to mediate increases in CBF. The outstanding questions are: (i) which substances are released by what cells and under which circumstances? (ii) What is the spatial specificity of with respect to the cortical architecture? (iii) What is the physiological role of vasoactive agents in the context of underlying physiological and pathophysiological processes, such as hypertension and stroke? The main research approach that we have adopted has been to combine state-of-the-art neuroimaging techniques, able to probe the brain across different spatial and temporal scales, with pharmacological manipulations aimed at determining the relative contribution, spatial specificity and cellular basis of the different pathways to the HRF. The main neuroimaging techniques to be used are anatomical and functional MRI, which are able to provide non-invasive images of the brain with sub-millimeter spatial resolution and superior soft tissue contrast. However, at its present spatial resolution, MRI can barely visualize cortical cytoarchitecture and it is certainly not yet able to resolve individual cells and capillary vessels. To understand neurovascular coupling one must be able to resolve the neurovascular unit and study its signaling mechanisms at the level of its individual cellular constituents. Two-photon microscopy is an attractive technique that allows simultaneous measurements of the activity of individual neurons and astrocytes, along with the corresponding changes in diameter and red blood cell velocities in individual vessels. However, the excellent spatial resolution of 2-photon microscopy comes at a price in 3D spatial coverage. Not only the depth of penetration is limited, but also the limitation in field-of-view prevents one from observing the feeding arteries and draining veins to the capillary network of interest, and thus the impact that the supply and drainage of blood has on the capillary response cannot be evaluated. Our lab believes that a way to get around such limitations and make forward progress is to combine the advantages of MRI and 2-photon microscopy into simultaneous or parallel multi-modal recordings, so that neurovascular coupling can be studied in all relevant spatial and temporal scales. In addition, incorporation of modern electrophysiology techniques able to probe neural activity across different cortical layers will add crucial data about the flow of information within a functional cortical column, and allow better interpretation of the temporal evolution of the hemodynamic response within that column. The integration of the above multi-modal techniques constitutes a powerful and attractive experimental approach that will shed light on the intricate mechanisms of CBF control. Current and future experiments will continue to focus on understanding the relevance of these pathways to neurovascular coupling in the presence of pathophysiological states such as hypertension and ischemic stroke. &#8232;&#8232; In the current review cycle, we have worked on understanding the influence of hypertension in stroke outcome. It is well known that hypertension is a major risk factor for ischemic stroke. However, the management of preexisting hypertension is still controversial in the treatment of acute stroke in hypertensive patients. So we sought out to evaluate the influence of preserving hypertension during focal cerebral ischemia on stroke outcome in a rat model of chronic hypertension, the spontaneously hypertensive rat (SHR). Focal cerebral ischemia was induced by transient (1h) occlusion of the middle cerebral artery, during which mean arterial blood pressure was maintained at normotension (110-120mm Hg, group 1, n=6) or hypertension (160-170mm Hg, group 2, n=6) using phenylephrine. T2-, diffusion- and perfusion-weighted MRI were performed serially at five different time points: before and during ischemia, and at 1, 4 and 7 days after ischemia. Lesion volume and brain edema were estimated from apparent diffusion coefficient maps and T2-weighted images. Regional cerebral blood flow (rCBF) was measured within and outside the perfusion deficient lesion and in the corresponding regions of the contralesional hemisphere. Neurological deficits were evaluated after reperfusion. Infarct volume, edema, and neurological deficits were significantly reduced in group 2 vs. group 1. In addition, higher values and rapid restoration of rCBF were observed in group 2, while rCBF in both hemispheres was significantly decreased in group 1. Maintaining preexisting hypertension alleviates ischemic brain injury in SHR by increasing collateral circulation to the ischemic region and allowing rapid restoration of rCBF. The data suggest that maintaining preexisting hypertension is a valuable approach to managing hypertensive patients suffering from acute ischemic stroke. This study was just published in Brain Research (Kang BT et al Brain Res 2012), and follows our previous study in Neuroimage (Leoni RF et al Neuroimagie 2011;58(1):75-81) demonstrating that hypertension, when combined with age, increases cerebrovascular resistance and reduces cerebrovascular compliance in a way that is hard to counteract acutely. Indeed, based on the above work, we have been investigating the correlation between temporal changes of regional cerebral blood flow (rCBF) and the severity of ischemic stroke in spontaneously hypertensive rats (SHR). T2-, diffusion- and perfusion-weighted magnetic resonance imaging were performed in Wistar-Kyoto rats (WKY) and SHR serially at six different time points; before and during 1 hour of middle cerebral artery occlusion (MCAO), 1 hour after reperfusion, and 1 day, 4 days and 7 days after MCAO. Regional CBF values were measured in both hemispheres. The area with three ranges of rCBF (0-6 (ischemic core), 6-15 (ischemic penumbra), and 15-23 (benign oligemia) mL/100 g/min) was measured. Most of the perfusion deficient lesion (33.953.68%) was progressed to ischemic lesion (33.025.41%) in SHR (P>0.05), but the final infarct volume of WKY (12.629.19%) was significantly smaller than the perfusion deficient lesion (32.524.08%) (P<0.01) and similar to the area with the lowest rCBF range (13.132.96%) (P>0.05). The regulation of CBF was lost in both hemispheres of SHR until 1 day after MCAO. There was no correlation between decreased blood supply and the final infarct volume (r=-0.443, P>0.05). Impaired CBF regulation and relatively high CBF threshold for infarction may greatly contribute to increased susceptibility of ischemic stroke in SHR. We are in final stages of submitting a manuscript to JCBFM reporting these findings.

我们感兴趣的是确定成熟的神经化学途径（例如 NO 和 COX-2）在塑造 CBF 调节的空间特异性中的生理作用。工作假设是，实质上关键位置的细胞释放的血管活性物质作用于脑血管并调节其张力以介导 CBF 的增加。悬而未决的问题是：（i）什么细胞在什么情况下释放哪些物质？ (ii) 皮质结构的空间特异性是什么？ (iii) 血管活性药物在潜在的生理和病理生理过程（例如高血压和中风）中的生理作用是什么？我们采用的主要研究方法是将最先进的神经影像技术与药理学操作相结合，这些技术能够在不同的空间和时间尺度上探测大脑，旨在确定 HRF 不同途径的相对贡献、空间特异性和细胞基础。 所使用的主要神经影像技术是解剖学和功能性 MRI，它们能够提供具有亚毫米空间分辨率和卓越软组织对比度的大脑非侵入性图像。然而，在目前的空间分辨率下，MRI 几乎无法可视化皮质细胞结构，而且它当然还无法解析单个细胞和毛细血管。为了理解神经血管耦合，我们必须能够解析神经血管单元并在其单个细胞成分水平上研究其信号传导机制。双光子显微镜是一种有吸引力的技术，可以同时测量单个神经元和星形胶质细胞的活动，以及单个血管中直径和红细胞速度的相应变化。然而，2 光子显微镜卓越的空间分辨率是以 3D 空间覆盖范围为代价的。不仅穿透深度有限，而且视野的限制也使得人们无法观察到感兴趣的毛细血管网络的供血动脉和引流静脉，因此无法评估血液的供应和引流对毛细血管反应的影响。我们实验室认为，克服这些限制并取得进展的一种方法是将 MRI 和 2 光子显微镜的优点结合到同步或并行多模态记录中，以便可以在所有相关的空间和时间尺度上研究神经血管耦合。此外，结合能够探测不同皮质层神经活动的现代电生理学技术，将添加有关功能性皮质柱内信息流的关键数据，并可以更好地解释该柱内血流动力学响应的时间演变。上述多模式技术的整合构成了一种强大且有吸引力的实验方法，它将揭示 CBF 控制的复杂机制。当前和未来的实验将继续侧重于了解在高血压和缺血性中风等病理生理状态存在下这些途径与神经血管耦合的相关性。 

 在当前的审查周期中，我们致力于了解高血压对中风结局的影响。众所周知，高血压是缺血性中风的主要危险因素。 然而，在高血压患者急性卒中的治疗中，对原有高血压的管理仍存在争议。因此，我们试图在慢性高血压大鼠模型（自发性高血压大鼠（SHR））中评估局灶性脑缺血期间保持高血压对卒中结果的影响。通过短暂（1小时）大脑中动脉闭塞诱发局灶性脑缺血，在此期间使用去氧肾上腺素将平均动脉血压维持在正常血压（110-120mm Hg，第1组，n = 6）或高血压（160-170mm Hg，第2组，n = 6）。在五个不同时间点连续进行 T2 加权、弥散加权和灌注加权 MRI：缺血前和缺血期间，以及缺血后 1、4 和 7 天。根据表观扩散系数图和 T2 加权图像估计病变体积和脑水肿。在灌注不足病变内部和外部以及对侧半球的相应区域测量区域脑血流量（rCBF）。再灌注后评估神经功能缺损。与第 1 组相比，第 2 组的梗塞体积、水肿和神经功能缺损均显着减少。此外，第 2 组中观察到 rCBF 值较高且快速恢复，而第 1 组中两个半球的 rCBF 均显着下降。维持先前存在的高血压可通过增加缺血区域的侧支循环并允许 rCBF 快速恢复来减轻 SHR 中的缺血性脑损伤。数据表明，维持原有高血压是治疗患有急性缺血性中风的高血压患者的一种有价值的方法。这项研究刚刚发表在 Brain Research (Kang BT et al Brain Res 2012) 上，并遵循了我们之前在 Neuroimage (Leoni RF et al Neuroimagie 2011;58(1):75-81) 上的研究，证明高血压与年龄相结合，会增加脑血管阻力并降低脑血管顺应性，而这种方式很难迅速抵消。事实上，基于上述工作，我们一直在研究自发性高血压大鼠（SHR）局部脑血流（rCBF）的时间变化与缺血性卒中严重程度之间的相关性。在 Wistar-Kyoto 大鼠 (WKY) 和 SHR 中连续六个不同时间点进行 T2 加权、扩散加权和灌注加权磁共振成像；大脑中动脉闭塞（MCAO）之前和期间1小时，再灌注后1小时，以及MCAO后1天、4天和7天。测量两个半球的区域 CBF 值。测量具有三个范围的 rCBF（0-6（缺血核心）、6-15（缺血半暗带）和 15-23（良性低血症）mL/100 g/min）的面积。 SHR中大部分灌注不足病灶（33.953.68%）进展为缺血性病灶（33.025.41%）（P>0.05），但WKY最终梗死体积（12.629.19%）显着小于灌注不足病灶（32.524.08%）（P<0.01），且面积相似具有最低的 rCBF 范围 （13.132.96%）（P>0.05）。直到 MCAO 后 1 天，SHR 的两个半球都失去了 CBF 的调节。血供减少与最终梗死体积之间无相关性（r=-0.443，P>0.05）。 CBF 调节受损和相对较高的梗塞 CBF 阈值可能会极大地增加 SHR 中缺血性卒中的易感性。我们正处于向 JCBFM 提交报告这些发现的手稿的最后阶段。