Central Mechanisms Underlying the Stress Dampening Effects of Acute Hypernatremia

描述(由申请人提供)：应激性生活事件会导致焦虑和高血压，并显著增加心血管疾病的风险，心血管疾病是美国主要的死亡原因。开发限制应激反应的策略，以预防情感和心血管疾病是该项目的长期目标。焦虑症，下丘脑-垂体 肾上腺(HPA)轴功能障碍和心血管对应激的反应性增强导致情感和心血管疾病的发生，限制这些应激反应指标可能是有疗效的。催产素(OT)被用于治疗应激相关疾病；然而，催产素受体(OTRs)的激活可以有不同的作用，因此，识别调节应激反应的特定OTRs可能会改善治疗。大细胞催产素神经元在高钠血症、血浆钠浓度(PNA+)升高时兴奋，导致中枢催产素水平持续升高。在啮齿类动物中，通过升高PNA+来驱动内源性OT的释放会导致OTRs的激活，从而抑制杏仁中央核(CEA)和下丘脑室旁核(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有关，有趣的是，OTR介导的对CRF神经元的抑制减少了焦虑样行为，钝化了HPA的激活，并减弱了心血管对应激的反应。确定这种情况发生的神经机制(S)是这项提议的主要目标。在这一点上，高钠血症与应激相互作用，增加了终纹床核(BNST)和外侧腹隔(LVS)的神经元激活，这些神经元表达OTRs，并与介导应激反应的脑区相连。正在进行的研究表明，在BNST和LVS表达OTR的神经元投射到CEA或起GABA能中间神经元的作用。这些结果表明，高钠血症激活了BNST和LVS释放OT的大细胞催产素能神经元，刺激GABA能神经元上表达的OTRs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利用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，验证大细胞OT神经元发送轴突，通过激活OTRs使BNST和LVS神经元去极化的假说。目的2将利用Cre诱导的腺相关病毒(AAV)和光遗传学来验证BNST和LVS中表达OTRs的神经元具有GABA能传出抑制CEA和PVN中CRF神经元的假说。目的3将删除小鼠BNST和LVS中的OTRs，以验证这些受体介导高钠血症应激抑制效应的假设。这些实验的完成将确定内源性释放的OT激活的OTRs的特定群体，以限制应激反应，从而产生重要的信息，可能指导治疗共病的情感和心血管疾病的发展。

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.