Synaptic Mechanisms Regulating Sympathetic Drive

描述(申请人提供)：在包括高血压和充血性心力衰竭在内的许多病理生理条件下，来自大脑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。已有研究表明，血管紧张素II(Ang II)通过抑制突触GABA的释放而增加PVN交感前神经元的兴奋性。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，Ang II和NO突触前活动的重要信号转导机制仍然知之甚少。在这一建议中，将以投射到大鼠延髓头端腹外侧区和脊髓中间外侧细胞柱的PVN神经元作为模型系统，验证下列特定假设：1)Ang II通过12-脂氧合酶产物激活的电压门控性K+通道和与抑制性G蛋白偶联的磷脂酶A2激活电压门控性K+通道，减少GABA能突触输入到PVN前交感神经元；2)一氧化氮通过抑制电压门控性K+通道促进GABA向PVN前交感神经元的释放；3)蛋白激酶G激活蛋白磷酸酶，形成电压门控性K+通道的KV1/Kv4亚单位位于PVN的GABA能突触前终末。这些假说将使用体内逆行追踪、大鼠脑片全细胞膜片钳记录和免疫细胞化学技术相结合的方法进行验证。这些研究将为中枢神经系统中Ang II和NO相互对立的突触前活动的基本细胞和信号机制提供重要的新信息。这些信息对于我们理解在生理和病理生理状态如高血压、心肌梗死和充血性心力衰竭中负责交感神经系统中枢调节的突触机制也很重要。

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.