Cell-specific Synaptic Plasticity in the Auditory Brainstem

项目摘要 作为细胞功能的必需元素，二价锌是大量酶的辅因子， 调节蛋白自从令人惊讶地发现锌集中在许多神经元的突触囊泡中， 兴奋性突触在大脑中，包括在超过50%的兴奋性突触前末梢在新皮质 许多研究人员已经研究了这种金属在神经传递过程中的可能作用。 尽管如此，由于缺乏针对神经生物学研究优化的锌选择性工具， 锌在突触传递过程中的作用直到最近才被发现。我们最近的研究， 格兰特，使用新的工具螯合和跟踪锌在中央突触，并建立锌作为一种抑制 兴奋性突触中的神经调质。在对单个突触前动作电位的反应中， 释放并抑制突触后谷氨酸AMPA受体（AMPAR）。此外，在重复突触 刺激，锌抑制突触外谷氨酸NMDA受体（NMDAR），并且是沿着 GPR39，一种假定的代谢型锌敏感受体，用于激活内源性大麻素信号传导， 谷氨酸释放抑制。这些影响是经验依赖，因为响亮的声音减少 突触前锌水平和取消锌抑制AMPAR，暗示锌在经验依赖性 AMPAR突触可塑性。建立一种新的内源性神经调质，在许多 兴奋性突触在整个大脑，揭示了这项工作的意义，并提出了三个问题， 兴奋性突触信号和听觉处理的基本重要性：a）什么是动力学 不同形式的锌介导的抑制，以及它们如何相互作用，并与谷氨酸 B）什么是分子机制 突触前锌水平的潜在的持久的、活动依赖性的变化，以及它们如何与 其他已建立的可塑性机制，以及c）听觉刺激触发锌的特征是什么 体内锌的释放以及锌的释放如何影响清醒动物的自发活动和声音诱发的活动。 解决这些问题不仅对锌生物学和听力领域有重大贡献， 研究，但也将揭示一般机制，将极大的兴趣，更广泛的神经科学 社区在目标1和2中，我们将采用体外脑切片实验，并使用听觉脑干 突触作为研究锌在神经传递和可塑性中的作用的模型。在目标3中，我们将采用 在体内成像，以调查这些机制在未麻醉的听皮层处理中的作用， 小鼠

Project Summary As an essential element for cellular function, divalent zinc is a cofactor in a large number enzymes and regulatory proteins. Since the surprising discovery that zinc is concentrated within synaptic vesicles in many excitatory synapses in the brain, including in more than 50% of excitatory presynaptic terminals in neocortical areas, numerous investigators have studied the possible roles of this metal during neurotransmission. Nonetheless, due to the paucity of zinc–selective tools optimized for neurobiological studies, the physiological roles of zinc during synaptic transmission remained elusive until recently. Our recent studies, funded by this grant, used novel tools for chelating and tracking zinc in central synapses and established zinc as an inhibitory neuromodulator in excitatory synapses. In response to a single presynaptic action potential, synaptic zinc is released and inhibits postsynaptic glutamate AMPA receptors (AMPARs). Moreover, during repetitive synaptic stimulation, zinc inhibits extrasynaptic glutamate NMDA receptors (NMDARs) and is necessary along with GPR39, a putative metabotropic zinc-sensing receptor, for activation of endocannabinoid signaling and glutamate release inhibition. These effects are experience-dependent because loud sound reduced presynaptic zinc levels and abolished zinc inhibition of AMPARs, implicating zinc in experience-dependent AMPAR synaptic plasticity. The establishment of a novel endogenous neuromodulator, acting in many excitatory synapses throughout the brain, reveals the significance of the work and poses three questions of fundamental importance to excitatory synaptic signaling and auditory processing: a) what are the dynamics of the different forms of zinc-mediated inhibition and how do they interact among themselves and with glutamate neurotransmission to shape excitatory glutamatergic signaling, b) what are the molecular mechanisms underlying long-lasting, activity-dependent changes in presynaptic zinc levels and how do they interact with other established plasticity mechanisms, and c) what are the characteristics of auditory stimuli that trigger zinc release in vivo and how does zinc release affect spontaneous and sound-evoked activity in awake animals. Answering these questions will contribute significantly not only to the fields of zinc biology and hearing research, but will also reveal general mechanisms that will be of great interest to the wider neuroscience community. In Aims 1 and 2, we will employ in vitro brain slice experiments and use auditory brainstem synapses as models for studying the role of zinc in neurotransmission and plasticity. In Aim 3, we will employ in vivo imaging to investigate the role of these mechanisms in auditory cortical processing in unanesthetized mice.