Patterned, Stimulus-Independent Neuronal Activity In the Developing Drosophila Visual System: Origin and Contribution to Synaptic Maturation

项目摘要/摘要 突触连接决定神经回路如何处理信息。理解力量和力量如何 建立这些联系的特异性是神经生物学的一个中心挑战。在美国的许多地方 发育中的哺乳动物大脑，刺激非依赖性神经元活动的刻板模式先于感觉- 受驱动的响应。这种发育活动是否以及如何引导突触组装在 已定义的单元类型和电路还没有被很好地理解。在这里，挑战很大程度上是由于规模和 哺乳动物大脑本身的复杂性：即使是在发育活动最活跃的视网膜 特征是，寻求突触水平问题的技术障碍是显著的。我们最近 在大脑中发现了类似的有模式的、与刺激无关的神经活动(PSINA，发音为“see-nah”)。 发育中的果蝇大脑。随着对其神经生物学知识的不断增长，它跨越了连接体 在行为方面，苍蝇在细胞类型和电路水平的研究方面是无与伦比的。PSINA是全球性的 与全脑、周期性的活动期和静止期相协调。在视觉系统中，每种细胞类型都参与 在PSINA中，具有不同和定型的活动时空模式。这些发育活动 在成人中，已知为突触伙伴的成对神经元之间的模式是相关的。我们的长期计划 目的是验证PSINA特定细胞类型的活动模式提炼新出现的 产生野生型突触强度和特异性的连接体。在这里，我们将通过以下方式努力实现这一目标 利用PSINA上的一个新的遗传句柄：Trpγ是一种对钙离子有微弱偏好的阳离子通道 野生型PSINA。在Trpγ突变体中，整个大脑的活动幅度降低了50%，并且 特定细胞类型的活动模式和突触数量会发生变化。Trpγ在1.5%的细胞中表达 大脑中的神经元。值得注意的是，只有这些神经元通过过度表达超极化通道而沉默 使PSINA衰减90%。这表明这个不同的~1,700 Trpγ表达组中的一些或全部(即 Trpγ+)神经元对于协调发育中的大脑中的PSINA是至关重要的。我们假设色氨酸γ+神经元 是特定细胞类型活动模式的来源。在目标1中，我们将识别单个Trpγ+神经元 支配视觉系统并测试这些神经元是否指定其突触后的活动模式 合伙人。确定这些图案的来源将使我们能够问它们是原因还是 突触和回路成熟的结果。在目标2中，我们将专注于一个特定的神经元，它是 研究了运动检测电路，并询问其突触后接触的强度在Trpγ中是否发生了变化 变种人。确定活动模式的细胞来源并了解PSINA对 突触的发展将允许我们可逆地沉默、改变或可能重新编程PSINA。有了这个 知识，我们将能够定义发展活动对结构和功能的贡献 突触和回路的成熟，到感觉处理，到学习、记忆和行为。

Project Summary/Abstract Synaptic connections determine how neural circuits process information. Understanding how the strength and specificity of these connections is established is a central challenge in neurobiology. In many parts of the developing mammalian brain, stereotyped patterns of stimulus-independent neuronal activity precede sensory- driven responses. Whether and how this developmental activity guides synapse assembly at the level of defined cell types and circuits is not well-understood. Here, much of the challenge is due to the size and complexity of the mammalian brain itself: Even in the retina, where developmental activity is best characterized, the technical barriers to pursuing synapse level questions are significant. We recently discovered analogous patterned, stimulus-independent neural activity (PSINA, pronounced `see-nah') in the developing Drosophila brain. With the ever-growing knowledge of its neurobiology, spanning the connectome to behavior, the fly is unmatched in its promise for cell type- and circuit- level studies. PSINA is globally coordinated with brain-wide, periodic active and silent phases. In the visual system, each cell type participates in PSINA with distinct and stereotyped spatio-temporal patterns of activity. These developmental activity patterns are correlated between pairs of neurons known to be synaptic partners in the adult. Our long term goal is to test the hypothesis that the cell-type-specific activity patterns of PSINA refine the emerging connectome to generate wild-type synaptic strength and specificity. Here, we will work toward this goal by leveraging a new genetic handle on PSINA: Trpγ, a cation channel with a weak preference for Ca2+, is required for wild-type PSINA. In trpγ mutants, the amplitude of activity is reduced by >50% across the whole brain, and cell-type-specific activity patterns and synapse numbers are altered. Trpγ is expressed in <1.5% of the neurons in the brain. Notably, silencing only these neurons by overexpressing a hyperpolarizing channel attenuates PSINA by >90%. This indicates that some or all of this diverse group of ~1,700 Trpγ-expressing (i.e. Trpγ+) neurons are critical to coordinating PSINA in the developing brain. We hypothesize that Trpγ+ neurons are the source of the cell-type-specific activity patterns. In Aim 1, we will identify individual Trpγ+ neurons that innervate the visual system and test if these neurons specify the activity patterns of their post-synaptic partners. Determining the origin of these patterns will allow us to ask whether they are the cause or consequence of synapse and circuit maturation. In Aim 2, we will focus on a specific neuron that is part of the well-studied motion detection circuit and ask if the strength of its post-synaptic contacts are altered in trpγ mutants. Identifying the cellular origin of the activity patterns and understanding the effect of PSINA on synaptic development will allow us to reversibly silence, alter, or possibly re-program PSINA. With this knowledge, we will be able to define the contribution of developmental activity to the structural and functional maturation of synapses and circuits, to sensory processing, to learning, memory, and behavior.