Asynchronous Glutamate Release in Vagal Afferent to NTS Neurotransmission

描述（由申请人提供）：肥胖及其相关病理（包括心血管疾病和糖尿病）的患病率增加，占美国医疗保健费用的很大比例。脑干内的神经回路对食物摄入和能量平衡提供关键的控制。在尾侧脑干中，孤立束核（NTS）整合来自内脏器官系统的迷走神经传入信息，启动稳态反射通路，包括控制食物摄入所必需的反射通路。在中枢，迷走神经传入汇聚形成孤立束（ST），并通过强兴奋突触与二级NTS神经元接触。在ST-NTS突触，动作电位侵袭释放多个谷氨酸囊泡，这些囊泡与末端去极化精确同步。这种强大的“同步”形式的谷氨酸释放被认为是ST-NTS突触快速神经传递的主要模式。然而，最近，我们从迷走神经事件的一个亚群中发现了一种新的活动依赖的“异步”谷氨酸释放形式。与同步释放相反，这种额外形式的神经传递仅与去极化松散协调，并持续数秒，有效地使突触强度加倍。由于额外的电荷转移，突触后兴奋期明显延长，显著改变了信息传递的性质。ST传入事件分为有髓鞘（a -纤维）和无髓鞘（c -纤维）表型，具有不同的生理功能。不同亚型之间的一个重要区别是c纤维传入表达钙渗透性非选择性离子通道“瞬时受体电位香草样蛋白1型”（TRPV1）。在我们的初步实验中，我们发现所有具有活性依赖的异步释放的事件也被TRPV1激动剂辣椒素激活。此外，TRPV1活性的拮抗选择性地减少了异步释放，而对同步释放没有影响。在TRPV1 KO小鼠中持续存在衰减的异步释放过程，并被钌红减少。综上所述，这些发现表明膜去极化内源性激活TRPV1和其他热敏- trp通道，这些通道在迷走神经传入中枢末梢表达，导致非同步谷氨酸释放。当前应用程序的目标是1。以描述TRPV1激活导致非同步谷氨酸释放的机制，2。2 .确定其他热TRPs参与非同步神经传递的程度；利用选择性拮抗剂和遗传KO小鼠模型来确定异步谷氨酸释放在控制食物摄入中的作用。该项目的研究结果将确定迷走神经传入的非同步谷氨酸释放的作用及其对食物摄入的影响。

DESCRIPTION (provided by applicant): The increased prevalence of obesity and its associated pathologies, including cardiovascular disease and diabetes mellitus, account for a large percentage of healthcare costs in the United States. Neurocircuitry within the brainstem provides critical controls of food intake and energy homeostasis. In the caudal brainstem the nucleus of the solitary tract (NTS) integrates vagal afferent information arriving from across visceral organ systems to initiate homeostatic reflex pathways, including those essential for the controls of food intake. Centrally, vagal afferents converge to form the solitary tract (ST) and contact second order NTS neurons via strong excitatory synapses. At ST-NTS synapses action-potential invasion releases multiple glutamate vesicles that are precisely synchronized with terminal depolarization. This robust 'synchronous' form of glutamate release is thought to be the predominate mode of fast neurotransmission at the ST-NTS synapse. Recently, however, we identified a novel form of activity-dependent 'asynchronous' glutamate release from a subgroup of vagal afferents. In contrast with synchronous release, this additional form of neurotransmission was only loosely coordinated with depolarization and continued for many seconds, effectively doubling the synaptic strength. As a result of the additional charge transfer the postsynaptic excitatory period was significantly extended, dramatically transforming the nature of information transfer. ST afferents are divided into myelinated (A-fiber) and unmyelinated (C-fiber) phenotypes with physiologically distinct functions. One important difference between subtypes is that C-fiber afferents express the calcium permeable non-selective ion channel 'transient receptor potential vanilloid type 1' (TRPV1). In our preliminary experiments we found all afferents with activity-dependent asynchronous release were also activated by the TRPV1 agonist capsaicin. Further, antagonism of TRPV1 activity selectively reduced the asynchronous release profile with no effect on synchronous. An attenuated asynchronous release process persists in TRPV1 KO mice and is reduced by ruthenium red. Together these findings suggest membrane depolarization endogenously activates TRPV1, and other thermosensitive-TRP channels, expressed in the central terminals of vagal afferents resulting in asynchronous glutamate release. The aims of the current application are 1. to delineate the mechanisms of TRPV1 activation resulting in asynchronous glutamate release, 2. determine the extent to which other thermo- TRPs participate in asynchronous neurotransmission, and 3. utilize selective antagonists and genetic KO mouse models to determine the contribution of asynchronous glutamate release in the control of food intake. The findings from this project will determine the role of asynchronous glutamate release from vagal afferents and its impact on food intake.