Mechanisms underlying neurovascular coupling

神经血管耦合（NVC）-神经元能量需求和局部血液供应之间的动态联系-对维持脑内稳态至关重要。在大脑中，增加的神经元突触活动伴随着局部脑血流量（CBF）的增加，其用于满足增加的葡萄糖和氧气需求。除了其重要的生理作用，更好地了解NVC的机制是非常重要的，因为这个概念是现代神经成像技术，如功能性磁共振成像（fMRI）和正电子发射断层扫描（PET）的基础。尽管这些技术实际上是测量脑氧、葡萄糖或CBF水平，并且这些变量与神经元活动之间的关系是非线性的，但结果仍然被错误地解释为神经元活动的直接反映。因此，必须更好地理解NVC背后的机制。在可能参与NVC的血管活性因子中，已经确定了一种强大的血管扩张剂和内源性产生的气体，一氧化氮（NO）。NO可潜在地作用于神经血管单位的所有类型的细胞（神经元、星形胶质细胞和血管细胞）。星形胶质细胞，这是唯一的定位之间的突触和血管，已被确认为神经元信号的整合，以中继信息的血管，可能是一个有趣的目标和NO的来源。我们确实证明，星形胶质细胞产生NO后，不同的神经刺激。目前的建议的主要重点是了解如何NO和星形胶质细胞信号通路相互作用在一起，以调节NVC。我们假设NO主要通过调节星形胶质细胞依赖性通路来调节NVC，但不是唯一的。为了验证这一假设，我们提出了三个具体的目标：1）阐明NO在NVC背景下对Ca 2+依赖的星形胶质细胞通路的作用; 2）阐明星形胶质细胞nNOS和eNOS介导的NO产生如何调节NVC ; 3）区分NVC中中间神经元、锥体神经元和星形胶质细胞中NO的重要性。这些机制将研究使用转基因小鼠和药理学工具与双光子显微镜和激光多普勒血流仪。所提出的概念是非常创新的，因为它假设NO是由神经元或内皮细胞产生的，作为血管扩张剂，而星形胶质细胞NO的潜在存在被忽略了。这也表明，星形胶质细胞中的每个组成型NOS与特定的通路相关，并可能与特定的功能相关。长期目标是确定NVC的潜在机制，并验证这些发现与MRI信号的相关性。相关性：本研究的结果将大大提高我们对脑血流与神经活动关系的认识，并有助于理解、改进和发展脑成像技术。

Neurovascular coupling (NVC) -the dynamic linkage between neuronal energy needs and local blood supply- is critical to the maintenance of brain homeostasis. In the brain, increased neuronal synaptic activity is accompanied by an increase in local cerebral blood flow (CBF) that serves to satisfy enhanced glucose and oxygen demand. Beside its crucial physiological role, a better understanding of the mechanisms underlying NVC is very important because this concept is at the basis of modern neuroimaging techniques such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). Despite the fact that these techniques are, in fact, measuring cerebral oxygen, glucose or CBF levels and that the relationship between these variables and neuronal activity are non-linear, results are still falsely interpreted as a direct reflection of neuronal activity. It is thus imperative to better understand the mechanisms underlying NVC. Among the vasoactive factors that could participate in NVC, one powerful vasodilator and endogenously produced gas have been identified, nitric oxide (NO). NO may potentially act on all type of cells of the neurovascular unit (neurons, astrocytes and vascular cells). Astrocytes, which are uniquely positioned between synapses and vessels, have been recognized as integrators of the neuronal signals to relay information to the vessels and could be an interesting target and source of NO. We indeed demonstrated that astrocytes produce NO upon different neurological stimulations. The major focus of the present proposal is to understand how NO and astrocytic signaling pathways interact together to modulate NVC. We HYPOTHETIZE that NO modulates NVC mostly but not uniquely by regulating astrocytic-dependent pathways. To verify this hypothesis, we propose three specific AIMS: 1) To elucidate the effect of NO on Ca2+-dependent astrocytic pathways in the context of NVC ; 2) To elucidate how astrocytic nNOS and eNOS mediated NO production regulates NVC ; 3) To discriminate the importance of NO from interneurons, pyramidal neurons and astrocytes in NVC. These mechanisms will be studied using transgenic mice and pharmacological tools with two-photon microscopy and laser Doppler flowmetry. The proposed concept is very INNOVATIVE because it is assumed that NO is produced by neurons or endothelial cells to act as vasodilators whereas the potential presence of astrocytic NO had been ignored. It also suggests that each constitutive NOS in astrocytes is associated to a specific pathway and possibly to a specific function. The LONG-TERM GOALS are to define the mechanisms underlying NVC and to verify how these findings correlate with MRI signals. RELEVANCE: results obtained from the present proposal will greatly enhance our understanging of how neural activity is related to CBF and may help to understand, improve and develop brain imaging techniques.