Diabetes suppresses sympathetic neurotransmission and thereby glucagon secretion

描述（由申请人提供）： 我们先前在非糖尿病动物和人类中已经表明，胰高血糖素对中度和显著胰岛素诱导的低血糖的反应大多数是由自主神经系统介导的。这种自主激活由中枢神经性血糖减少症引起，包括直接刺激胰高血糖素分泌的胰腺交感神经的激活。最近的数据表明，交感神经的激活可以显着抑制，即使是短期的糖尿病高血糖症：在体外，高葡萄糖损害的烟碱乙酰胆碱受体（nAChR）的激活，需要跨原型交感神经节的神经传递。在体内，我们的初步数据表明，对投射到胰岛的交感神经元的烟碱激活的显著抑制。这些数据可以解释为什么在非自身免疫性糖尿病发展后不久，胰高血糖素对胰岛素诱导的低血糖的反应在动物中丢失，尽管在疾病的早期阶段没有结构性神经病变。因此，本项目的总体目标是确定糖尿病高血糖与交感神经节神经传递抑制的关系，并确定这种抑制对糖尿病胰高血糖素反应受损的贡献。我们的第一个具体目标是确定抑制交感神经-胰岛通路中神经节神经传递所需的糖尿病高血糖的程度和持续时间，以及干预措施预防或逆转这种抑制的能力。我们将激活腹腔神经节交感神经元上的烟碱乙酰胆碱受体，并比较非糖尿病和糖尿病动物之间的fos mRNA反应。我们将通过使用一种新的SGLT 2抑制剂达格列净增加尿糖排泄来改变糖尿病高血糖的程度，不使用胰岛素。我们将简单地通过调整实验的长度来改变糖尿病高血糖的持续时间。为了确定逆转高血糖诱导的交感神经节神经传递的抑制需要多长时间，我们将通过向STZ糖尿病大鼠的脑室输注瘦素来恢复正常，而不使用胰岛素.为了防止高血糖症诱导的交感神经节神经传递抑制，我们将使用沃勒变性缓慢（Wlds）大鼠，我们的新的初步数据显示其对这种形式的神经功能障碍具有抗性。我们的第二个具体目标将系统地检查糖尿病中所见的胰高血糖素反应受损的神经节神经传递抑制的功能后果。首先，我们将通过使用Wlds大鼠来防止高血糖诱导的交感神经节神经传递的抑制，以证明其使胰高血糖素对节前神经刺激的反应正常化。其次，我们还将评估抗氧化剂治疗逆转交感神经节神经传递抑制和恢复胰高血糖素反应的疗效。我们将使用这些方法来确定抑制的交感神经激活对α细胞对胰岛素诱导的低血糖反应的总体损害的具体贡献，因为糖尿病诱导的这种胰高血糖素反应的损害可能是由于多种因素。

DESCRIPTION (provided by applicant): We have previously shown in non-diabetic animals and humans that the majority of the glucagon response to both moderate and marked insulin-induced hypoglycemia is mediated by the autonomic nervous system. This autonomic activation is caused by central neuroglucopenia and includes activation of pancreatic sympathetic nerves, which directly stimulate glucagon secretion. Very recent data demonstrate that activation of sympathetic nerves can be markedly suppressed by even short-term diabetic hyperglycemia: in vitro, high glucose impairs the activation of the nicotinic acetylcholine receptor (nAChR) that is required for neurotransmission across a prototypic sympathetic ganglion. In vivo, our preliminary data demonstrate marked suppression of nicotinic activation of the sympathetic neurons that project to the pancreatic islet Such data may explain why the glucagon response to insulin-induced hypoglycemia is lost in animals so soon after the development of non-autoimmune diabetes, despite the absence of structural neuropathies at this early stage of the disease. Therefore, the overall goal of this project is to determine the relationship of diabetic hyperglycemia to this suppression of sympathetic ganglionic neurotransmission and to determine the contribution of this suppression to impaired glucagon responses in diabetes. Our first Specific Aim is to determine the magnitude and duration of diabetic hyperglycemia needed to suppress ganglionic neurotransmission in the sympathetic-islet pathway and the ability of interventions to prevent or reverse that suppression. We will activate nicotinic acetylcholine receptors on the sympathetic neurons in the celiac ganglion and compare their fos mRNA responses between non-diabetic and diabetic animals. We will vary the magnitude of diabetic hyperglycemia, without insulin, by increasing urinary glucose excretion with a new SGLT2 inhibitor, dapagliflozin. We will vary the duration of diabetic hyperglycemia simply by adjusting the length of the experiment. To determine how long it takes to reverse the hyperglycemia- induced suppression of sympathetic ganglionic neurotransmission, we will restore euglycemia, without insulin, by infusing leptin into the cerebral ventricles of STZ diabetic rats. To prevent hyperglycemia-induced suppression of sympathetic ganglionic neurotransmission, we will use the Wallerian Degeneration Slow (Wlds) rat which our new Preliminary Data show to be resistant to this form of neural dysfunction. Our second Specific Aim will systematically examine the functional consequences of suppressed ganglionic neurotransmission for the impaired glucagon responses seen in diabetes. First we will prevent hyperglycemia- induced suppression of sympathetic ganglionic neurotransmission by using Wlds rats to demonstrate that it normalizes the glucagon response to the preganglionic nerve stimulation. Second, we will also evaluate the efficacy of antioxidant treatment to both reverse this suppression of sympathetic ganglionic neurotransmission and to restore this glucagon response. We will use these approaches to determine the specific contribution of that suppressed sympathetic activation makes to the overall impairment of the alpha cell's response to insulin- induced hypoglycemia, since the diabetes-induced impairment of this glucagon response may be due to multiple factors.