Acute Corticosteriod Actions in the Hypothalamus

描述(由申请人提供)：压力与下丘脑-垂体-肾上腺(HPA)轴的激活和循环中肾上腺皮质类固醇水平的增加有关。糖皮质激素反馈到下丘脑，不仅抑制促肾上腺皮质激素释放激素(CRH)的分泌和HPA的激活，而且还抑制许多其他下丘脑神经内分泌系统。糖皮质激素的负反馈调节发生在两个阶段：急性抑制CRH的释放，缓慢下调下丘脑室旁核(PVN)神经元CRH和加压素的合成。到目前为止，糖皮质激素对下丘脑神经分泌的负反馈调节作用在大脑的哪个部位发挥作用，以及这种反馈的细胞机制是什么，目前还不清楚。这些问题对于治疗影响大量人群的广泛的情感障碍具有深远的意义，包括压力、抑郁和饮食障碍。本研究的总体目的是确定PVN神经内分泌系统的急性糖皮质激素负性调节是否直接发生在PVN内的激素分泌神经元，并表征这种调节的细胞机制。我们有初步证据表明，PVN中糖皮质激素的快速抑制作用是通过激活膜受体和释放逆行的内源性大麻素信使来实现的，该信使抑制兴奋性并促进抑制传入PVN神经元。基于这些发现，我们建议在大鼠急性下丘脑脑片上进行全细胞膜片钳记录，以检验以下特定假设：1.糖皮质激素通过刺激内源性大麻素抑制谷氨酸释放和促进GABA释放直接抑制PVN神经元；2.糖皮质激素通过激活突触后G蛋白偶联受体和脂质信使信号级联激活PVN神经元逆行释放内源性大麻素；3.内大麻素介导的PVN谷氨酸和GABA释放的变化是由突触前、G蛋白和蛋白激酶依赖的信号机制介导的。这些研究将首次揭示下丘脑中快速糖皮质激素作用的部位和生理机制。下丘脑中糖皮质激素的快速反馈在机体对应激的整体反应中起着至关重要的作用，了解下丘脑中糖皮质激素的作用机制将为HPA相关病理的治疗提供重要的细胞靶点。此外，糖皮质激素-内源性大麻素之间的联系为下丘脑功能和大麻素之间的相互作用提供了有趣的可能性。

DESCRIPTION (provided by applicant): Stress is associated with activation of the hypothalamic-pituitary-adrenal (HPA) axis and increased levels of circulating adrenal corticosteroids. Glucocorticoids feed back onto the hypothalamus to inhibit not only corticotropin releasing hormone (CRH) secretion and HPA activation, but also many other hypothalamic neuroendocrine systems. The negative feedback regulation by glucocorticoids occurs in two stages: an acute inhibition of the release of CRH, and a slower down-regulation of CRH and vasopressin synthesis in neurons of the hypothalamic paraventricular nucleus (PVN). To date, it is not known where in the brain glucocorticoids exert their negative feedback regulation of hypothalamic neurosecretion, and what the cellular mechanisms of this feedback are. These questions have profound significance for the treatment of widespread affective disorders, including stress, depression, and eating disorders, that impact large numbers of people. The overall purpose of this proposal is to determine whether acute negative glucocorticoid regulation of PVN neuroendocrine systems occurs directly at the hormone-secreting neurons in the PVN, and to characterize the cellular mechanisms of this regulation. We have preliminary evidence for rapid inhibitory glucocorticoid effects in the PVN mediated by membrane receptor activation and the release of a retrograde endocannabinoid messenger that suppresses excitatory and facilitates inhibitory inputs to PVN neurons. Based on these findings, we propose to conduct whole-cell patch-clamp recordings in acute rat hypothalamic slices to test the following specific hypotheses: 1. glucocorticoids inhibit PVN neurons directly by stimulating an endocannabinoid-mediated suppression of glutamate release and facilitation of GABA release; 2. glucocorticoids elicit retrograde endocannabinoid release from PVN neurons by activation of a postsynaptic G protein-coupled receptor and lipid messenger signaling cascade; 3. the endocannabinoid-mediated changes in glutamate and GABA release in the PVN are mediated by presynaptic, G protein- and protein kinase-dependent signaling mechanisms. These studies will reveal for the first time the site and physiological mechanisms of fast glucocorticoid actions in the hypothalamus. Fast glucocorticoid feedback in the hypothalamus plays a critical role in the organism's holistic response to stress, and understanding the mechanisms of glucocorticoid actions in the hypothalamus will provide important cellular targets for the treatment of HPA-related pathologies. Furthermore, the glucocorticoid-endocannabinoid link opens interesting possibilities for interactions between hypothalamic function and the cannabinoids.