Neural Mechanisms in Congestive Heart Failure

描述（由申请人提供）：过度的交感神经系统活动是充血性心力衰竭（CHF）发病的主要因素。产生交感神经兴奋状态有两个关键因素。首先，CHF患者血浆血管紧张素II （ANG II）水平升高，可在脑内增加交感神经活动（SNA）。其次，慢性细胞外液积聚降低心肺反射功能，从而抑制SNA。这些发现是本研究的关键，因为下丘脑室旁核（PVN）中的神经元既需要ANG II升高的交感兴奋作用，也需要体积扩张的交感抑制作用。实验将在结扎左冠状动脉前降支致CHF大鼠和假手术对照大鼠中进行。我们将验证这样的假设，即CHF的交感神经亢进是由于ANG ii介导的PVN突触输入增加造成的，并且由于gaba介导的心肺反射抑制同时减少，这具有增强的兴奋作用。在Aim 1中，将确定PVN中急性GABA-A和ANG II AT1受体阻断对正在进行的肾脏和腰椎SNA水平的影响。将对不同CHF水平的大鼠进行效果比较。研究还将确定在CHF中SNA对ANG II和GABA输入PVN的生理激活的反应是如何改变的。在Aim 2中，我们将记录个体RVLM-， IML-和nts -投射PVN神经元对体内体积/机械敏感心肺输入和ANG ii敏感输入激活的反应。我们预计，心力衰竭患者PVN单位对心肺输入的反应将显著减弱。反过来，假设这使得中枢ANG II的交感神经兴奋作用相对不受反对。因此，我们预计ANG II对SNA和PVN单元放电的影响将增强。在Aim 3中，将从RVLM、IML和NTS逆行标记的PVN神经元制备脑切片，并在体外进行全细胞膜片钳记录。我们将确定CHF中每个细胞组突触活动的振幅和频率是如何改变的。我们将确定ANG II和GABA输入在调节PVN神经元兴奋性中的相互作用，以及这些在CHF中如何改变。最后，我们还将确定CHF如何改变突触后去极化、放电和向内电流对ANG II的反应。该研究首次在确定的交感调节神经元中检测CHF中突触可塑性的机制。这一信息将对导致CHF交感神经激活和疾病严重程度进展的过程产生新的和潜在的重要见解。

DESCRIPTION (provided by applicant): Exaggerated sympathetic nervous system activity is a major contributor to the pathogenesis of congestive heart failure (CHF). Two factors appear critical in producing the sympathoexcitatory state. First, an elevated level of plasma angiotensin II (ANG II) in CHF acts within the brain to increase sympathetic nerve activity (SNA). Second, chronic extracellular fluid accumulation reduces cardiopulmonary reflex function and thus inhibitory restraint of SNA. These findings are key to the present proposal because neurons in the hypothalamic paraventricular nucleus (PVN) are required for both the sympathoexcitatory actions of elevated ANG II as well as the sympathoinhibitory effects of volume expansion. Experiments will be performed in rats with CHF induced by ligating the left anterior descending coronary artery and in sham-operated control rats. We will test the hypothesis that sympathetic hyperactivity in CHF results from increased ANG II-mediated synaptic input to the PVN and that this has an enhanced excitatory effect due to a concurrent reduction in GABA-mediated cardiopulmonary reflex inhibition. In Aim 1, effects of acute GABA-A and ANG II AT1 receptor blockade in the PVN on the level of ongoing renal and lumbar SNA will be determined. Effects will be compared among rats with graded levels of CHF. Studies will also determine how SNA responses to physiological activation of ANG II and GABA inputs to the PVN are altered in CHF. In Aim 2, we will record the response of individual RVLM-, IML- and NTS-projecting PVN neurons to activation of volume-/mechanosensitive cardiopulmonary inputs and ANG II-sensitive inputs in vivo. We anticipate that PVN unit responses to cardiopulmonary input will be significantly attenuated in CHF. This, in turn, is postulated to leave sympathoexcitatory effects of central ANG II relatively unopposed. Therefore, we expect ANG II effects on SNA and PVN unit discharge to be enhanced. In Aim 3, brain slices will be prepared and whole cell patch-clamp recordings will be performed in vitro from PVN neurons retrogradely labelled from the RVLM, IML and NTS. We will determine how the amplitude and frequency of synaptic activity are altered in each cell group in CHF. We will determine interactions between ANG II and GABA inputs in regulating PVN neuronal excitability and how these are altered in CHF. Finally, we will also determine how postsynpatic depolarization, discharge and inward current responses to ANG II are altered in CHF. The proposed studies are the first to examine mechanisms of synaptic plasticity in CHF among identified sympathetic-regulatory neurons. This information will yeild new and potentially important insight into the processes that lead to sympathetic activation and progression of disease severity in CHF.