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主要并发症是低血糖相关自主神经衰竭（HAAF）的发展。在该综合征的急性形式中，24小时内经历两次或更多次低血糖会导致神经内分泌反调节反应的减弱，而神经内分泌反调节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进行模拟，似乎代表了一种“压力适应”形式。对于其他压力源，反复暴露于相同的压力源会导致神经内分泌压力对该压力的反应减弱。我们已经建立了HAAF大鼠模型，并发现，当大鼠在24小时内暴露于三次（相对于一次）低血糖发作时，伴随着神经内分泌反应减弱，大脑激活模式（反映在c-fos的表达上）发生改变。特别是，c-fos在下丘脑室旁核（PVN）和背内侧核（DMH）区域减少，而对PVN有净抑制输入的丘脑室旁核后区（THPVP）的激活没有变化。我们得出结论，PVN的刺激输入（DMH）减少和抑制输入（THPVP）不变的组合可能在PVN的神经激活减少中发挥重要作用，从而降低下游神经内分泌激活。在这一系列的研究中，我们建议测试这两个脑区域的作用，这两个脑区域在调解神经内分泌对其他类型的应激源的反应，在低血糖应激的神经内分泌反应和HAAF的发展中是重要的。我们将使用利多卡因或抑制性GABA类似物muscimol可逆地灭活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，我们将验证以下假设：在经历第三轮低血糖的大鼠中，PVN抑制输入的净增加（通过gabaergy传递反映）通过阻断PVN中的gabaergy活性导致HAAF的表达。总之，这些研究将为两个应激调节脑区在正常的低血糖反调节反应和HAAF表达中的作用提供新的见解；他们将进一步验证PVN在介导低血糖反调节中的作用。

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.