Asynchronous Glutamate Release in Vagal Afferent to NTS Neurotransmission

描述（由申请方提供）：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。脑干内的神经回路提供食物摄入和能量稳态的关键控制。在尾侧脑干中，孤束核（NTS）整合来自内脏器官系统的迷走传入信息，以启动稳态反射通路，包括控制食物摄入所必需的通路。在中枢，迷走神经传入纤维会聚形成孤束（ST），并通过强兴奋性突触接触二级NTS神经元。在ST-NTS突触，动作电位侵入释放多个谷氨酸囊泡，这些囊泡与末端去极化精确同步。谷氨酸释放的这种强大的“同步”形式被认为是ST-NTS突触处快速神经传递的主要模式。然而，最近，我们发现了一种新的形式的活动依赖性的“异步”谷氨酸释放迷走神经传入的一个亚组。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地协调，并持续许多秒，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，极大地改变了信息传递的性质。ST传入分为有髓（A-纤维）和无髓（C-纤维）表型，具有生理上不同的功能。亚型之间的一个重要差异是C纤维传入表达钙渗透性非选择性离子通道“瞬时受体电位香草酸1型”（TRPV 1）。在我们的初步实验中，我们发现所有具有活动依赖性异步释放的传入神经也被TRPV 1激动剂辣椒素激活。此外，TRPV 1活性的拮抗作用选择性地降低了异步释放曲线，对同步释放没有影响。衰减的异步释放过程持续在TRPV 1基因敲除小鼠，并减少钌红。总之，这些研究结果表明，膜去极化内源性激活TRPV 1和其他热敏TRP通道，表达在迷走神经传入的中枢末梢，导致异步谷氨酸释放。本申请的目的是1.阐明TRPV 1激活导致谷氨酸非同步释放的机制，2.确定其他热TRP参与异步神经传递的程度，以及3.利用选择性拮抗剂和基因敲除小鼠模型来确定非同步谷氨酸释放在控制食物摄入中的作用。该项目的发现将确定迷走神经传入的异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.