CNS Stress Pathways and the Development of Acute HAAF

描述（由申请人提供）：需要胰岛素的糖尿病患者的一个主要并发症是发生低血糖相关的自主神经功能衰竭或HAAF。在急性形式的综合征中，在24小时内经历两次或更多次低血糖发作导致神经内分泌反调节反应钝化，该反应通常会纠正血糖水平。这种现象可以在非糖尿病人类和实验动物中模拟，似乎代表了一种“压力适应”形式。对于其他应激源，重复暴露于相同的应激源会导致神经内分泌应激对该应激的反应钝化。我们已经建立了一个HAAF大鼠模型，发现当大鼠在24小时内暴露于三次（相对于一次）低血糖发作时，伴随着钝化的神经内分泌反应，脑激活模式（反映在c-fos的表达中）发生改变。具体c-fos减少室旁核（PVN）和背内侧（DMH）下丘脑区，与丘脑后室旁核（THPVP）的激活没有变化，该区域具有净抑制输入的PVN。我们的结论是，减少刺激性输入（DMH）和不变的抑制性输入（THPVP）的PVN的组合可能在减少PVN的神经激活，从而减少下游神经内分泌激活中发挥了重要作用。在这一系列的研究中，我们建议测试这两个大脑区域的作用，这是重要的神经endocnne对其他类型的应激反应的调解，在神经内分泌对低血糖应激反应和HAAF的发展。我们将用利多卡因或抑制性GABA类似物蝇蕈醇可逆地阻断THPVP和DMH，并测量神经内分泌对低血糖的反应，分别假设HAAF逆转或HAAF模拟的结果。此外，我们将测试以下假设：PVN处抑制性输入的净增加（由GABA能传递反映）通过阻断正在经历第三轮低血糖的大鼠PVN中的GABA能活性而引起HAAF的表达。总之，这些研究将提供新的见解的作用，两个应激调节脑区在正常的反调节反应低血糖，并在HAAF的表达，他们将进一步验证PVN介导的反调节低血糖的作用。

DESCRIPTION (provided by applicant): A major complication for insulin-requiring diabetic individuals is the development of Hypoglycemia Associated Autonomic Failure, or HAAF. In the acute form of the syndrome the experience of two or more bouts of hypoglycemia within a 24-hour period results in a blunting of the neuroendocnne counterregulatory response which would normally correct plasma glucose levels. This phenomenon can be modeled in non-diabetic humans and experimental animals, and appears to represent a form of 'stress adaptation'. With other stressors, repeated exposure to the same stressor results in a blunting of the neuroendocrine stress response to that stress. We have developed a rat model of HAAF and have found that, concomitant with the blunted neuroendocnne response, patterns of brain activation (reflected in expression of c-fos) are altered when rats are exposed to three (vs. one) bouts of hypoglycemia in a 24-hr period. Specifically c-fos was decreased in the paraventricular (PVN) and dorsomedial (DMH) hypothalamic areas, with no change in activation of the posterior paraventricular nucleus of the thalamus (THPVP), a region which has net inhibitory input to the PVN. We concluded that a combination of decreased stimulatory input (DMH) and unchanged inhibitory input (THPVP) to the PVN may play a significant role in the decreased neural activation of the PVN and thus decreased downstream neuroendocrine activation. In this series of studies we propose to test the roles of these two brain areas, which are important in the mediation of neuroendocnne responses to other types of stressors, in the neuroendocrine response to hypoglycemic stress and in the development of HAAF. We will reversibly inactivate the THPVP and the DMH with lidocaine or the inhibitory GABA analog muscimol and measure neuroendocnne responses to hypoglycemia, with hypothesized outcomes of reversal of HAAF or simulation of HAAF, respectively. Additionally, we will test the hypothesis that a net increase of inhibitory input at the PVN (reflected by GABAergic transmission) causes the expression of HAAF, by blocking GABAergic activity in the PVN in rats that are experiencing a third bout of hypoglycemia. Together these studies will provide new insight into the role of two stress-regulatory brain regions in the normal counterrregulatory response to hypoglycemia, and in the expression of HAAF; and they will further validate the role of the PVN in mediating counterregulation to hypoglycemia.