NITRIC OXIDE IN FOCAL CEREBRAL ISCHEMIA

有显著数据表明，脑缺血是伴随着 通过细胞外兴奋性氨基酸的增加。有证据表明 最近积累的与这些兴奋性氨基酸增加有关的 神经细胞组织中一氧化氮的产生。体外实验数据 强烈提示一氧化氮在脑组织中起着重要作用 缺血，虽然在体内获得的有限数据，是 模棱两可。这个项目的主要目的是解决明显的 通过仔细地研究一个 各种参数。在猫局灶性脑缺血模型中，一氧化氮 对缺血和缺血后组织的产生将通过 各种技术，包括直接测量一氧化氮 一氧化氮合酶活性测定微电极 一氧化氮合酶免疫组织化学染色(神经元、内皮和 巨噬细胞一氧化氮合酶)和NADPH黄递酶染色。脑血流量会 使用两个激光多谱勒进行连续测量，在一个 区域和用于多个离散测量的放射性标记微球 各地区的。为了进一步研究一氧化氮可能 脑缺血功能、微血管通透性测定 也将被制作成。暂时性闭塞会产生局灶性缺血 在猫的左侧大脑中动脉，测量将是 在急性和慢性缺血阶段进行。利用 抑制一氧化氮合成的化合物，或 增加组织中的一氧化氮水平，我们将确定是否程度 神经元组织损伤可以通过改变一氧化氮的产生来改变。 该项目的主要假设是，体内的局部一氧化氮 脑组织产生一种反作用力的平衡，其中一些作用于 减少脑缺血造成的损害(即血管扩张，这是由于 血管平滑肌上的一氧化氮)，以及一些作用于增强 脑缺血损伤(即一氧化氮在组织中的毒性作用)。 通过适当修饰一氧化氮合酶的活性，从而 减轻缺血时组织中一氧化氮的增加 对血液流动产生不利影响，我们将能够减少 脑缺血后的神经元损伤。使用起作用的药物 优先表达于神经细胞和内皮细胞构成的一氧化氮 合酶，在酶的诱导形式上，我们将获得 神经元、血管内皮细胞和 诱导型一氧化氮合成。只有多管齐下， 在同一动物模型中测量了许多参数，我们会 能够弄清一氧化氮在大脑中扮演的真正角色 缺血症。随着对脑损伤机制的更好的理解 对于缺血性损伤，可以更直接地设计治疗方案。如果 作用于一氧化氮/精氨酸系统的化合物被证明是 神经保护，它将为治疗提供另一种潜在的途径 脑缺血的症状。

There is significant data indicating the cerebral ischemia is accompanied by an increase in extracellular excitatory amino acids. Evidence has recently accumulated linking the increase in these excitatory amino acids with the production of nitric oxide in neuronal tissue. The in vitro data strongly suggests a significant role for nitric oxide int he cerebral ischemia, while the limited data that has been obtained in vivo, is equivocal. The principal aim of this project is to resolve the apparent discrepancies int he literature by performing careful studies looking at a variety of parameters. In a focal ischemia model in the cat, nitric oxide production in ischemic and postischemic tissue will be monitored by a variety of techniques including the direct measurement of nitric oxide with a microelectrode, measurement of nitric oxide synthase activity, nitric oxide synthase immunohistochemical staining (for neuronal, endothelial, and macrophage NOS), and NADPH diaphorase staining. Cerebral blood flow will be measured using both laser doppler for continuous measurements in one region, and radiolabeled microspheres for discrete measurements in a number of regions. To further investigate the mechanism by which nitric oxide may function in cerebral ischemia, measurements of microvascular permeability will also be made. Focal ischemia will be produced by temporary occlusion of the left middle cerebral artery int he cat, and measurements will be undertaken in both the acute and the chronic stage of ischemia. Utilizing compounds that inhibit the synthesis of nitric oxide, or compounds that increase tissue nitric oxide levels, we will determine if the extent of neuronal tissue damage can be altered by altering nitric oxide production. The primary hypothesis of this project is that local nitric oxide in cerebral tissue produces a balance of opposing forces, some acting to reduce damage in cerebral ischemia (ie. vasodilation, due to the action of nitric oxide ont he vascular smooth muscle), and some acting to augment cerebral ischemic damage (ie. toxic action of nitric oxide in the tissue). By appropriately modifying the activity of nitric oxide synthase so as to attenuate the tissue nitric oxide increases that occur in ischemia without adversely affecting blood flow, we will be able to reduce the extent of neuronal damage following cerebral ischemia. Using drugs which act preferentially on the neuronal and endothelial constitutive nitric oxide synthase, and on the inducible form of the enzyme, we will obtain information on the relateive importance of neuronal, endothelial, and inducible nitric oxide synthesis. Only by using a multi-prong approach, where a number of parameters are measured int he same animal model, will we be able to sort out the true role that nitric oxide plays in cerebral ischemia. With a better understanding of the mechanisms of cerebral ischemic injury, treatment protocols can more directly be designed. If compounds that act on the nitric oxide/arginine system are shown to be neuroprotective, it will provide another potential avenue for the treatment of cerebral ischemia.