Impact of Nicotinic Signaling through Astrocytes on Glutamate Synapse Formation

描述（由申请人提供）：谷氨酸能突触包括大脑中的主要兴奋性通路。确定突触能突触强度的一个关键特征是可用于激活的突触后AMPA受体的数量。我们有初步的证据表明，尼古丁刺激星形胶质细胞导致他们释放一种成分，专门招募AMPA受体的突触后神经元的网站，使这些以前的“沉默”突触功能。这是完全出乎意料的，并提出了一个新的和重要的机制，塑造兴奋性电路。星形胶质细胞是无处不在的和丰富的时候，神经元突触是第一次形成在发展过程中，并有显着数量的？7-含有烟碱乙酰胆碱受体（？7-nAChR）。自发性烟碱胆碱能活性部分通过？7-nAChR在发育早期也广泛存在。我们的初步证据表明是这些？7-负责星形胶质细胞对AMPA受体的作用的nAChR。鉴于星形胶质细胞和？7-nAChR信号，这种机制可能对塑造网络形成和功能输出产生深远的影响。第一个具体目标将测试在细胞培养中的突触的影响，释放独特的尼古丁刺激星形胶质细胞的成分？7-nAChR。将检查突触能突触的突触前和突触后成分，评估突触功能，并开始筛选候选成分。第二个具体目标将测试体内的假设，使用病毒结构和GFAP-Cre系统在突变小鼠，以确定是否星形胶质细胞？7-nAChR在海马神经元上募集突触后AMPA受体中起关键作用。随后的实验将测试星形胶质细胞？7-nAChR也有助于突触可塑性，集中在以前的研究表明，长期增强的结果从AMPA受体的数量增加的位置。除了提供对大脑基本过程的新见解外，这些研究还将具有重要的生物医学意义。发现尼古丁信号会影响神经元突触的功能等基本特征，如果早期暴露于尼古丁（如二手烟或母乳），可能会使系统在发育过程中处于高风险状态，过早刺激或脱敏这种调节输入。此外，这些结果将直接关系到制药公司的全球目标？7-nAChRs在药物设计中没有意识到星形胶质细胞？7-nAChR可能具有这种独特和关键的作用。这个R21项目将测试中心假设，并为未来了解星形胶质细胞和烟碱信号在调节神经系统形式和功能中的作用的项目奠定基础。

DESCRIPTION (provided by applicant): Glutamatergic synapses comprise the major excitatory pathways in brain. A key feature determining the strength of a glutamatergic synapse is the number of postsynaptic AMPA receptors available for activation. We have preliminary evidence that nicotinic stimulation of astrocytes causes them to release a component that specifically recruits AMPA receptors to postsynaptic sites on neurons, rendering these previously "silent" synapses functional. This is completely unexpected and suggests a new and important mechanism for shaping excitatory circuits. Astrocytes are pervasive and abundant when glutamatergic synapses are first forming during development, and have significant numbers of ?7-containing nicotinic acetylcholine receptors (?7-nAChRs). Spontaneous nicotinic cholinergic activity mediated in part through ?7-nAChRs is also widespread early in development. Our preliminary evidence suggests that it is these ?7-nAChRs that are responsible for the astrocyte effect on AMPA receptors. In view of the early appearance and widespread occurrence of astrocytes and ?7-nAChR signaling, such a mechanism could have profound consequences for shaping network formation and functional output. The first Specific Aim will test in cell culture the synaptogenic effects of components released uniquely by nicotinic stimulation of astrocyte ?7-nAChRs. Pre- and postsynaptic components at glutamatergic synapses will be examined, synaptic function assessed, and a screen of candidate components initiated. The second Specific Aim will test the hypothesis in vivo, using viral constructs and a GFAP-Cre system in mutant mice to determine if astrocyte ?7-nAChRs play a critical role in recruiting postsynaptic AMPA receptors on neurons in the hippocampus. Subsequent experiments will test whether astrocyte ?7-nAChRs also contribute to synaptic plasticity, focusing on locations where previous studies have shown that long-term potentiation results from increased numbers of AMPA receptors. In addition to providing new insight into fundamental processes in the brain, these studies will have serious biomedical implications. Finding that nicotinic signaling influences such basic features as the functionality of glutamatergic synapses may put the system at high risk during development if exposed early on to nicotine, such as through secondhand smoke or maternal milk, either prematurely stimulating or desensitizing this regulatory input. Further, the results will have immediate relevance for pharmaceutical companies globally targeting ?7-nAChRs in drug design without realizing that astrocyte ?7-nAChRs may have this unique and critical role. This R21 project will test the central hypotheses and lay the groundwork for future projects understanding the role of astrocytes and nicotinic signaling in regulating nervous system form and function.