Vanzetta Ivo, Hildesheim Rina, Grinvald Amiram
Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel.
J Neurosci. 2005 Mar 2;25(9):2233-44. doi: 10.1523/JNEUROSCI.3032-04.2005.
Optical imaging, positron emission tomography, and functional magnetic resonance imaging (fMRI) all rely on vascular responses to image neuronal activity. Although these imaging techniques are used successfully for functional brain mapping, the detailed spatiotemporal dynamics of hemodynamic events in the various microvascular compartments have remained unknown. Here we used high-resolution optical imaging in area 18 of anesthetized cats to selectively explore sensory-evoked cerebral blood-volume (CBV) changes in the various cortical microvascular compartments. To avoid the confounding effects of hematocrit and oximetry changes, we developed and used a new fluorescent blood plasma tracer and combined these measurements with optical imaging of intrinsic signals at a near-isosbestic wavelength for hemoglobin (565 nm). The vascular response began at the arteriolar level, rapidly spreading toward capillaries and venules. Larger veins lagged behind. Capillaries exhibited clear blood-volume changes. Arterioles and arteries had the largest response, whereas the venous response was smallest. Information about compartment-specific oxygen tension dynamics was obtained in imaging sessions using 605 nm illumination, a wavelength known to reflect primarily oximetric changes, thus being more directly related to electrical activity than CBV changes. Those images were radically different: the response began at the parenchyma level, followed only later by the other microvascular compartments. These results have implications for the modeling of fMRI responses (e.g., the balloon model). Furthermore, functional maps obtained by imaging the capillary CBV response were similar but not identical to those obtained using the early oximetric signal, suggesting the presence of different regulatory mechanisms underlying these two hemodynamic processes.
光学成像、正电子发射断层扫描和功能磁共振成像（fMRI）都依赖血管反应来对神经元活动进行成像。尽管这些成像技术已成功用于脑功能图谱绘制，但不同微血管腔室中血液动力学事件的详细时空动态仍不清楚。在此，我们在麻醉猫的18区使用高分辨率光学成像，以选择性地探究各种皮质微血管腔室中感觉诱发的脑血容量（CBV）变化。为避免血细胞比容和血氧测定变化的混杂影响，我们开发并使用了一种新型荧光血浆示踪剂，并将这些测量与血红蛋白（565 nm）在近等吸收波长下的固有信号光学成像相结合。血管反应始于小动脉水平，迅速向毛细血管和小静脉扩散。较大的静脉反应滞后。毛细血管呈现出明显的血容量变化。小动脉和动脉的反应最大，而静脉反应最小。在成像过程中，使用605 nm照明（已知该波长主要反映血氧测定变化，因此与电活动的关系比CBV变化更直接）获得了有关特定腔室氧张力动态的信息。这些图像截然不同：反应始于实质水平，其他微血管腔室随后才出现反应。这些结果对fMRI反应模型（例如球囊模型）具有启示意义。此外，通过对毛细血管CBV反应进行成像获得的功能图谱与使用早期血氧测定信号获得的图谱相似但不完全相同，这表明这两个血液动力学过程背后存在不同的调节机制。
