Masamoto Kazuto, Hoshikawa Ryo, Kawaguchi Hiroshi
Brain Science Inspired Life Support Research Center, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan.
Curr Top Med Chem. 2016;16(24):2677-84. doi: 10.2174/1568026616666160413135207.
An adequate supply of blood flow to the brain is critically important to maintain long-term brain function. However, many issues surrounding the regulatory mechanism of the blood flow supply to the brain remain unclear, such as i) the appropriate range of capillary flow velocity to keep neurons healthy, ii) the size of the vascular module to support a functioning neural unit, iii) the sensing mechanism for capillary flow control, and iv) the role of flow regulation in promoting neural plasticity. A fluorescence technique allows for visualization of the dynamic changes between cerebral microcirculation and neural activity concurrently and thus is capable of addressing these questions. Here, we briefly review the methodological aspects of measuring blood flow using fluorescence imaging in rodent brains and introduce a novel approach for mapping the flow velocity in multiple vessels with laser scanning fluorescence microscopy. The flow velocity was imaged by calculating the traveling distance and time of the instantaneously injected fluorescent tags through the vascular networks. Using the present method, we observed that the average flow velocity in the pial artery and vein was 3.0 ± 1.4 mm/s and 1.6 ± 0.5 mm/s, respectively (N = 6 mice). A limitation of the method presented is that the quantification is only applicable to the vascular networks laid in two-dimensional planes, such as pial vascular networks. Further technical improvement is needed to quantify three-dimensional flow through parenchymal microcirculation. Furthermore, it is also needed to fill a gap between the microscopically measured flow parameters and the macroscopic feature of the brain blood flow for clinical interpretation.
充足的脑血流供应对于维持长期脑功能至关重要。然而，围绕脑血流供应调节机制的许多问题仍不明确，例如：i）保持神经元健康的毛细血管流速的适当范围；ii）支持功能正常的神经单元的血管模块大小；iii）毛细血管血流控制的传感机制；iv）血流调节在促进神经可塑性中的作用。荧光技术能够同时可视化脑微循环与神经活动之间的动态变化，因此能够解决这些问题。在此，我们简要回顾在啮齿动物脑内使用荧光成像测量血流的方法学方面，并介绍一种利用激光扫描荧光显微镜绘制多条血管流速的新方法。通过计算瞬间注入的荧光标记物在血管网络中的行进距离和时间来成像流速。使用本方法，我们观察到软脑膜动脉和静脉中的平均流速分别为3.0±1.4毫米/秒和1.6±0.5毫米/秒（N = 6只小鼠）。所提出方法的一个局限性在于，定量仅适用于二维平面中的血管网络，如软脑膜血管网络。需要进一步的技术改进来定量通过实质微循环的三维血流。此外，还需要填补微观测量的血流参数与脑血流宏观特征之间的差距，以便进行临床解读。
