Spontaneous activity in the developing cochlea

发育中的耳蜗的自发活动

• 批准号: 7371184
• 负责人: DWIGHT E BERGLES
• 金额: $ 34.85万
• 依托单位: JOHNS HOPKINS UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-12-01 至 2010-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7371184
• 关键词: ATP Receptors; Acoustic Nerve; Action Potentials; Acute; Afferent Neurons; Anions; Auditory; Automobile Driving; Biological Preservation; Brain; Brain Stem; Cell Communication; Cell Nucleus; Cells; Characteristics; Cochlea; Condition; Connexins; Dendrites; Development; Event; Exhibits; Fire - disasters; Frequencies; Gap Junctions; Generations; Growth; Hair Cells; Hearing; Human; Image; Inner Hair Cells; Inner Supporting Cell; Ions; Lead; Maintenance; Maps; Measures; Mediating; Membrane; Membrane Potentials; Monitor; Mutation; Nerve; Nerve Fibers; Neurons; Optics; Organ of Corti; Outer Hair Cells; Pattern; Permeability; Physiological; Play; Property; Proteins; Purinergic P2 Receptors; Rattus; Relative (related person); Resistance; Rest; Rodent; Role; Sensory; Signal Transduction; Stimulus; Supporting Cell; Synapses; Testing; Time; Tinnitus; Tissues; Whole-Cell Recordings; afferent nerve; auditory pathway; caged IP3; deafness; extracellular; fluorescence imaging; human GJB2 protein; inhibitor/antagonist; photolysis; response; sensory system; sound; spiral ganglion

DESCRIPTION (provided by applicant): Spontaneous activity in developing sensory systems has been shown to be important for the growth and survival of projection neurons as well as the refinement and stabilization of sensory maps in the brain. In the developing cochlea, bursts of action potentials occur in afferent spiral ganglion neurons prior to the onset of hearing, activity that has been traced to inner hair cells (IHCs). Although IHCs are capable of generating Ca2+ action potentials during this period, the depolarizing stimulus required to initiate these events has not been identified. Whole-cell recordings from IHCs and supporting cells located adjacent in IHCs in ex vivo cochleas from young rodents revealed the presence of spontaneous inward currents that were capable of inducing large depolarizations. This activity was coincident with changes in the optical properties of the tissue when visualized using IR/DIC imaging, indicating that these events can be monitored non- invasively. Spontaneous electrical and optical activity was blocked by P2 purinergic receptor antagonists and gap junction inhibitors, suggesting that ATP and gap junctions/hemichannels are involved in initiating these events. Remarkably, this activity is no longer observed after the onset of hearing. This discovery of spontaneous purinergic signaling in the developing organ of Corti raises many new questions about the mechanisms responsible for producing this activity, the role that this ATP-mediated signaling plays in driving afferent firing, and the cause of the disappearance of the activity after hearing onset. We hypothesize that these ATP driven depolarizations of IHCs are responsible for initiating activity in developing auditory pathways. The preservation of this activity in both acute and cultured cochleas in which appropriate cell- cell interactions are maintained provides us with an unprecedented opportunity to understand the mechanisms responsible for these robust phenomena. We propose to use IR/DIC and confocal fluorescence imaging, photolysis, and both whole cell and extracellular recording to investigate the mechanisms underlying spontaneous activity in supporting cells and hair cells in the developing organ of Corti. These studies will evaluate the specific hypothesis that spontaneous oscillations in [Ca2+]i within supporting cells triggers both inward currents and the release of ATP that depolarizes IHCs.Relevance The studies outlined in this proposal seek to understand the mechanisms responsible for initiating spontaneous activity in supporting cells, hair cells, and afferent dendrites in the developing cochlea. This activity has been shown to have a profound influence on survival of target neurons in brainstem nuclei, the physiological properties of these auditory neurons, and the pattern of synaptic connectivity in these regions. Most congenital forms of deafness result from mutations in connexin 26, a gap junction protein highly expressed by cochelar supporting cells. As our preliminary results suggest that connexin hemichannels may play a role in ATP release from supporting cells, the studies outlined here may help explain how these mutations lead to deafness. Furthermore, these studies may reveal one mechanism by which activity can be induced in afferent nerves in the absence of sound, which may have direct relevance to human conditions such as tinnitus.

描述（由申请人提供）：发展中的感觉系统中的自发活动对于投射神经元的生长和存活以及大脑中感觉图的完善和稳定至关重要。在发育中的耳蜗中，在听力发作之前，传染性的螺旋神经节神经元中发生了动作电位爆发，这已追溯到内毛细胞（IHC）。尽管在此期间，IHC能够产生Ca2+动作电位，但尚未确定启动这些事件所需的去极化刺激。来自IHCS的全细胞记录和位于IHC附近的幼啮齿动物的IHC中的支撑细胞显示出存在能够诱导大型去极化的自发内向电流。当使用IR/DIC成像可视化时，该活性与组织的光学特性的变化一致，这表明这些事件可以非侵入性地监测。 P2嘌呤能受体拮抗剂和间隙连接抑制剂阻断了自发的电和光活性，这表明ATP和GAP连接/半通道参与了启动这些事件。值得注意的是，听证会后不再观察到这种活动。在Corti发育的器官中发现自发的嘌呤能信号传导引发了许多有关负责产生此活动的机制的新问题，该ATP介导的信号在驱动传入的发射方面起着作用以及听力发作后活动消失的原因。我们假设这些ATP驱动的IHC驱动去极化是负责在开发听觉途径中启动活动的原因。维持适当的细胞相互作用的急性和培养的耳蜗中这种活性的保存为我们提供了前所未有的机会，可以理解负责这些强大现象的机制。我们建议使用IR/DIC和共聚焦荧光成像，光解以及全细胞和细胞外记录来研究Corti发育器官中支持细胞和毛细胞的自发活性的机制。这些研究将评估以下具体假设：在支持细胞内[Ca2+] I中的自发振荡触发了内向电流和ATP的释放，该ATP的释放使IHCS.RELEVANCE中概述了该提议中概述的研究旨在理解负责在支持细胞，毛发细胞，毛发和副词中的自发性活性的机制。该活性已被证明对靶神经元在脑干核的存活，这些听觉神经元的生理特性以及这些区域突触连通性的模式具有深远的影响。大多数先天性的耳聋形式是由连接素26突变引起的，连接素26（一种由Cchelar支持细胞高度表达的间隙连接蛋白。由于我们的初步结果表明，连接蛋白半通道可能在支持细胞中的ATP释放中发挥作用，因此此处概述的研究可能有助于解释这些突变如何导致耳聋。此外，这些研究可能揭示了一种机制，在没有声音的情况下，可以在传入神经中诱导活性，这可能与人类条件（如耳鸣）直接相关。