Diabetes suppresses sympathetic neurotransmission and thereby glucagon secretion

描述(由申请人提供)： 我们之前已经在非糖尿病动物和人类身上表明，对于中度和显著的胰岛素诱导的低血糖，大多数胰升糖素的反应是由自主神经系统调节的。这种自主神经的激活是由中枢神经糖素减少引起的，包括胰腺交感神经的激活，这直接刺激了胰高血糖素的分泌。最近的数据表明，交感神经的激活甚至可以被短期的糖尿病高血糖显著抑制：在体外，高糖损害了烟碱型乙酰胆碱受体(NAChR)的激活，这是通过典型交感神经节进行神经传递所必需的。在体内，我们的初步数据显示，投射到胰岛的交感神经元的尼古丁激活明显受到抑制。这些数据可能解释了为什么动物在非自身免疫性糖尿病发生后这么快就失去了对胰岛素诱导的低血糖的胰升糖素反应，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患者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-胰岛通路中神经节细胞神经传递所需的糖尿病高血糖的程度和持续时间，以及预防或逆转这种抑制的干预能力。我们将激活腹腔神经节交感神经元上的烟碱型乙酰胆碱受体，并比较非糖尿病动物和糖尿病动物的FOS mRNA反应。我们将在不使用胰岛素的情况下，通过使用新的SGLT2抑制剂达伐他汀增加尿糖排泄来改变糖尿病高血糖的程度。我们将通过调整实验的长度来改变糖尿病高血糖的持续时间。为了确定需要多长时间才能逆转高血糖引起的交感神经节神经传递抑制，我们将通过将瘦素注入STZ糖尿病大鼠的脑室来恢复正常血糖，而不使用胰岛素。为了防止高血糖引起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表明，它对这种形式的神经功能障碍具有抵抗力。我们的第二个具体目标将系统地研究抑制的神经节细胞神经传递对糖尿病患者中受损的胰高血糖素反应的功能后果。首先，我们将通过使用Wlds大鼠来预防高血糖引起的交感神经节神经传递抑制，以证明高血糖可以正常节前神经刺激对胰高血糖素的反应。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效果。我们将使用这些方法来确定抑制交感神经激活对α细胞对胰岛素诱导的低血糖反应的整体损害的具体贡献，因为糖尿病引起的这种胰高血糖素反应的损害可能是由多种因素引起的。

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.