Synaptic Mechanisms Regulating Sympathetic Drive

描述（由申请人提供）：在许多病理生理条件下，包括高血压和充血性心力衰竭，从大脑发出的交感神经驱动增加。下丘脑室旁核（PVN）是控制交感神经流出的重要部位，它通过投射到脑干和脊髓的交感神经相关部位。研究表明，血管紧张素II（Ang II）通过减弱突触GABA的释放而增加PVN前交感神经元的兴奋性。另一方面，一氧化氮（NO）通过增强GABA能输入抑制PVN前交感神经元。然而，重要的信号转导机制负责突触前的行动，血管紧张素II和NO仍然知之甚少。本研究拟以投射到延髓腹外侧头端和脊髓中间外侧细胞柱的PVN神经元为模型系统，验证以下假说：1）Ang Ⅱ通过与抑制性G蛋白偶联的12-脂氧合酶产物和磷脂酶A2激活的电压门控性K+通道，减少GABA能突触对PVN前交感神经元的输入; 2）由于蛋白激酶G激活蛋白磷酸酶，一氧化氮通过抑制电压门控K+通道增强GABA在PVN前交感神经元上的突触释放; 3）形成电压门控K+通道的Kv 1/Kv 4亚基位于PVN中GABA能突触前末梢上。将使用体内逆行追踪、大鼠脑切片中的全细胞膜片钳记录和免疫细胞化学技术的组合来测试这些假设。这些研究将提供重要的新信息的基本细胞和信号机制的对立突触前作用的血管紧张素II和NO在中枢神经系统。这些信息也将是重要的，我们了解的突触机制负责中枢调节交感神经系统的生理和病理生理状态，如高血压，心肌梗死，充血性心力衰竭。

DESCRIPTION (provided by applicant): The sympathetic drive emanating from the brain is increased in many pathophysiological conditions including hypertension and congestive heart failure. The paraventricular nucleus (PVN) of the hypothalamus is an important site for the control of sympathetic outflow through its projections to the sympathetically related sites in the brainstem and spinal cord. It has been shown that angiotensin II (Ang II) increases the excitability of PVN presympathetic neurons by attenuation of the synaptic GABA release. On the other hand, nitric oxide (NO) inhibits PVN presympathetic neurons through potentiation of the GABAergic input. However, the important signal transduction mechanisms responsible for the presynaptic actions of Ang II and NO remain poorly understood. In this proposal, PVN neurons that project to the rostral ventrolateral medulla and spinal intermediolateral cell column in rats will be used as a model system to test the following specific hypotheses: 1) Ang II reduces the GABAergic synaptic input to PVN presympathetic neurons through voltage-gated K+ channels activated by 12-lipoxygenase products and phospholipase A2 coupled to inhibitory G proteins; 2) Nitric oxide potentiates synaptic GABA release onto PVN presympathetic neurons through inhibition of voltage-gated K+ channels, due to activation of protein phosphatases by protein kinase G; and 3) Kv1/Kv4 subunits that form voltage-gated K+ channels are located on GABAergic presynaptic terminals in the PVN. These hypotheses will be tested using a combination of in vivo retrograde tracing, whole-cell patch-clamp recording in rat brain slices, and immunocytochemistry techniques. These studies will provide important new information about the fundamental cellular and signaling mechanisms for the opposing presynaptic actions of Ang II and NO in the central nervous system. This information also will be important for our understanding of the synaptic mechanisms responsible for central regulation of the sympathetic nervous system in physiological and pathophysiological states such as hypertension, myocardial infarction, and congestive heart failure.