Asynchronous Glutamate Release in Vagal Afferent to NTS Neurotransmission

描述(申请人提供)：肥胖症及其相关疾病，包括心血管疾病和糖尿病，在美国的医疗费用中占很大比例。脑干内的神经回路提供了食物摄入量和能量平衡的关键控制。在尾侧脑干，孤束核(NTS)整合了来自内脏器官系统的迷走神经传入信息，以启动动态平衡反射通路，包括那些对控制食物摄入量至关重要的通路。在中枢，迷走神经传入汇聚形成孤束(ST)，并通过强兴奋性突触与二阶NTS神经元联系。在ST-NTS突触，动作电位的侵入释放了多个与末端去极化精确同步的谷氨酸小泡。这种强劲的“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，我们从迷走神经传入的一个亚群中发现了一种新的依赖活动的“异步”谷氨酸释放形式。与同步释放相比，这种额外的神经传递形式只与去极化松散地协调，并持续了许多秒，有效地使突触强度加倍。由于额外的电荷转移，突触后兴奋期显著延长，极大地改变了信息转移的性质。ST传入神经元分为有髓(A-纤维)和无髓(C-纤维)两种表型，具有不同的生理功能。亚型之间的一个重要区别是C纤维传入表达非选择性钙离子通道的瞬时受体电位香草样物质类型1(TRPV1)。在我们的初步实验中，我们发现所有依赖活性的非同步释放的传入神经也被TRPV1激动剂辣椒素激活。此外，拮抗TRPV1活性选择性地降低了异步化释放谱，而对同步化没有影响。在TRPV1 KO小鼠体内存在减弱的非同步释放过程，并被Ru红还原。总之，这些发现表明，膜去极化内源性激活了TRPV1和其他温度敏感的Trp通道，这些通道在迷走神经传入的中央终末表达，导致谷氨酸的异步释放。目前应用的目的是：1.阐明TRPV1激活导致谷氨酸非同步释放的机制；2.确定其他温度-TRP参与非同步神经传递的程度；3.利用选择性拮抗剂和遗传KO小鼠模型来确定非同步谷氨酸释放在控制摄食量中的作用。该项目的发现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取的影响。

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.