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)发病机制的主要因素。有两个因素似乎是产生交感兴奋状态的关键。首先，CHF患者血浆血管紧张素II(Ang II)水平升高会在脑内起作用，增加交感神经活动(SNA)。第二，慢性细胞外液积聚降低了心肺反射功能，从而抑制了SNA的抑制。这些发现是目前这一提议的关键，因为下丘脑室旁核(PVN)中的神经元既需要升高的Ang II的交感兴奋作用，也需要交感抑制容量扩张的作用。实验将在结扎左冠状动脉前降支诱导的CHF大鼠和假手术对照组大鼠身上进行。我们将验证一种假设，即CHF的交感神经过度活动是由于血管紧张素II介导的突触传入PVN增加所致，并且由于GABA介导的心肺反射抑制的同时减少，这具有增强的兴奋效应。在目标1中，将确定急性阻断PVN内GABA-A和Ang II AT1受体对正在进行的肾脏和腰椎SNA水平的影响。将在CHF分级水平的大鼠之间进行效果比较。研究还将确定SNA对Ang II和GABA输入到PVN的生理激活的反应在CHF中是如何改变的。在目标2中，我们将在体内记录单个RVLM、IML和NTS投射的PVN神经元对容量/机械敏感的心肺输入和Ang II敏感输入的反应。我们预计心衰时室旁核单位对心肺输入的反应将显著减弱。反过来，这又被认为使中枢Ang II的交感兴奋效应相对不被对抗。因此，我们预计Ang II对SNA和PVN单位放电的影响将会增强。在目标3中，将制备脑片，并在体外对从RVLM、IML和NTS逆行标记的PVN神经元进行全细胞膜片钳记录。我们将确定在CHF的每个细胞组中突触活动的幅度和频率是如何改变的。我们将确定Ang II和GABA输入之间在调节PVN神经元兴奋性方面的相互作用，以及这些在CHF中是如何改变的。最后，我们还将确定CHF中突触后去极化、放电和内向电流对Ang II的反应是如何改变的。这项拟议的研究是第一次在已识别的交感神经调节神经元中检查CHF中突触可塑性的机制。这些信息将对导致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.