Mechanisms underlying neurovascular coupling

神经血管偶联(NVC)-神经元能量需求和局部血液供应之间的动态联系-对维持大脑稳态至关重要。在大脑中，神经元突触活动的增加伴随着局部脑血流量(CBF)的增加，以满足增加的葡萄糖和氧气需求。除了其重要的生理作用外，更好地了解NVC的机制也非常重要，因为这一概念是现代神经成像技术(如功能磁共振成像(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大脑氧、葡萄糖或脑血流量水平，而且这些变量和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直接反映神经元活动。因此，必须更好地了解NVC背后的机制。在可能参与NVC的血管活性因子中，已发现一种强大的血管扩张剂和内源性气体，即一氧化氮(NO)。NO可能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)。星形胶质细胞位于突触和血管之间，被认为是神经元信号的整合者，将信息传递给血管，可能是一个有趣的靶点和NO的来源。我们确实证明了星形胶质细胞不会产生不同的神经刺激。本研究的重点是了解NO和星形胶质细胞信号通路如何相互作用来调节NVC。我们推测，NO主要通过调节星形胶质细胞依赖的通路来调节NVC，但不是唯一的。为了验证这一假说，我们提出了三个具体的目标：1)阐明NO在NVC背景下对钙依赖的星形细胞通路的影响；2)阐明星形胶质细胞nNOS和eNOS介导的NO产生如何调节NVC；3)区分来自中间神经元、锥体神经元和星形胶质细胞的NO在NVC中的重要性。这些机制将使用转基因小鼠和双光子显微镜和激光多普勒血流计的药理学工具进行研究。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，而潜在的星形细胞NO的存在被忽略了。它还表明，星形胶质细胞中的每个构成一氧化氮合酶都与特定的途径有关，可能与特定的功能有关。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：本研究的结果将极大地加强我们对神经活动与脑血流的关系的理解，并可能有助于理解、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.