Central Mechanisms Underlying the Stress Dampening Effects of Acute Hypernatremia

描述（由申请人提供）：压力性生活事件促进焦虑和高血压，并显着增加心血管疾病的风险，这是美国死亡的主要原因。开发限制压力反应以预防情感和心血管疾病的策略是该项目的长期目标。焦虑，下丘脑垂体 肾上腺（HPA）轴功能障碍和增强的心血管对应激的反应性有助于情感和心血管疾病的发作，限制这些应激反应指数可能是治疗性的。催产素（OT）被用于治疗与压力相关的疾病;然而，催产素受体（OTR）的激活可能具有不同的效果，因此，识别调节压力反应的特定OTR可能会改善治疗。大细胞OT神经元被高钠血症兴奋，血浆钠浓度（pNa+）增加，这导致OT中枢水平的长期增加。在啮齿动物中通过升高pNa+驱动内源性OT释放引起OTR的激活，OTR抑制中央杏仁核（CeA）和室旁核（PVN）中的促肾上腺皮质激素释放因子（CRF）神经元。这些神经元与焦虑和高血压的病因学有关，有趣的是，OTR介导的CRF神经元抑制减少了焦虑样行为，减弱了HPA激活并减弱了对应激的心血管反应。确定发生这种情况的神经机制是本提案的主要目标。在这方面，高钠血症与应激相互作用，以增加终纹床核（BNST）和腹侧隔（LVS）中的神经元活化，其表达OTR并连接到介导应激反应的脑区域。正在进行的研究表明，在BNST和LVS中表达OTR的神经元投射到CeA或作为GABA能中间神经元起作用。这些结果表明，高钠血症激活大细胞催产素能神经元，在BNST和LVS中释放OT，刺激GABA能神经元上表达的OTR，抑制CRF神经元，从而减轻焦虑，HPA激活和心血管对应激的反应。目的1将使用具有OTR特异性Cre表达的小鼠，神经解剖学追踪和体外膜片钳电生理学来验证大细胞OT神经元通过激活OTR来发送轴突以使BNST和LVS中的神经元退化的假设。目的2将利用Cre诱导的腺相关病毒（AAV）和光遗传学来验证在BNST和LVS中表达OTR的神经元具有抑制CeA和PVN中的CRF神经元的GABA能传出的假设。目的3将删除小鼠BNST和LVS中的OTR，以检验这些受体介导高钠血症的应激抑制作用的假设。这些实验的完成将确定由内源性释放的OT激活以限制应激反应的特定OTR群体，从而产生可指导共病情感和心血管疾病的治疗剂开发的重要信息。

DESCRIPTION (provided by applicant): Stressful life events promote anxiety and hypertension and significantly increase the risk for cardiovascular disease which the leading cause of death in the U.S. Developing strategies that limit stress responding to prevent affective and cardiovascular disorders is the long-term goal of this project. Anxiety, hypothalamic pituitary adrenal (HPA) axis dysfunction and enhanced cardiovascular reactivity to stress contribute to the onset of affective and cardiovascular disorders and limiting these indices of stress responding may be therapeutic. Oxytocin (OT) is being used to treat stress-related disorders; however, activation of oxytocin receptors (OTRs) can have diverse effects, and consequently, identifying specific OTRs regulating stress responding may improve treatments. Magnocellular OT neurons are excited by hypernatremia, increases in the plasma sodium concentration (pNa+), and this results in long-lasting increases in central levels of OT. Driving endogenous OT release by elevating the pNa+ in rodents causes activation of OTRs that inhibit corticotropin-releasing-factor (CRF) neurons in the central amygdala (CeA) and paraventricular nucleus of the hypothalamus (PVN). These neurons are implicated in the etiology of anxiety and hypertension, and intriguingly, OTR mediated inhibition of CRF neurons decreased anxiety-like behavior, blunted HPA activation and attenuated cardiovascular responses to stress. Determining the neural mechanism(s) by which this occurs is the main objective of this proposal. In this regard, hypernatremia interacts with stress to increase neuronal activation in the bed nucleus of the stria terminalis (BNST) and the lateral ventral septum (LVS), which express OTRs and connect to brain regions mediating stress responding. Ongoing studies suggest that OTR expressing neurons in the BNST and LVS project to the CeA or function as GABAergic interneurons. These results suggest that hypernatremia activates magnocellular oxytocinergic neurons that release OT in the BNST and LVS, stimulating OTRs expressed on GABAergic neurons that inhibit CRF neurons, thereby attenuating anxiety, HPA activation and cardiovascular responses to stress. Aim 1 will use mice with OTR-specific Cre expression, neuroanatomical tract-tracing and in vitro patch-clamp electrophysiology to test the hypothesis that magnocellular OT neurons send axons that depolarize neurons in the BNST and LVS by activating OTRs. Aim 2 will utilize Cre-inducible adenoassociated virus (AAV) and optogenetics to test the hypothesis that neurons expressing OTRs in the BNST and LVS have GABAergic efferents that inhibit CRF neurons in the CeA and PVN. Aim 3 will delete OTRs in the BNST and LVS of mice to test the hypothesis that these receptors mediate the stress dampening effects of hypernatremia. Completion of these experiments will determine the specific population of OTRs that are activated by endogenously released OT to limit stress responding, thereby producing important information that may guide the development of therapeutics for comorbid affective and cardiovascular disorders.