The role of activity in auditory system development

描述（由申请人提供）：已证明发育中的感觉系统的自发活动对投射神经元的生长和存活很重要，并可能有助于改善和稳定大脑中的感觉图。最近在体内的研究表明，动作电位的爆发发生在传入螺旋神经节神经元的听力发作之前，但负责产生这种活动的机制尚未确定。我们的初步研究表明，内毛细胞（IHC）在发育中的耳蜗周期性去极化的ATP，是从邻近的支持细胞自发释放。这些ATP依赖的去极化可以触发内毛细胞中的Ca 2+动作电位，这表明细胞外ATP可能负责启动听觉神经纤维的活动。在这里，我们建议测试这样的假设：在听力开始之前，初级传入螺旋神经节神经元的“自发”活动需要嘌呤能受体激活。我们将使用耳蜗外植体培养制备的prehearing大鼠的螺旋神经节神经元自发活动的模式，并确定这种活动是否依赖于ATP受体，并需要间隙连接/半通道。此外，我们将研究在体内的螺旋神经节神经元的放电模式，从这些神经元在prehearing大鼠的细胞外记录。为了测试螺旋神经节神经元的体内放电是否由ATP介导，我们将P2受体拮抗剂注入耳蜗，同时记录这些神经元的细胞外动作电位。这些实验试图确定听觉神经纤维在听前阶段的活动模式，并确定这种活动是否由耳蜗内ATP的释放介导。最终，从这些机制研究中获得的数据将使我们能够在体内操纵这种活动，以确定活动在听觉系统发育中发挥的特定作用。公共卫生相关性：该提案旨在确定负责在听力开始之前启动听觉神经中的感觉无关活动的机制。由于我们的初步研究结果表明，支持细胞释放的ATP可能在启动这种活动中发挥重要作用，这些研究可能会产生新的见解，了解间隙连接和其他支持细胞相关基因的突变如何导致耳聋。此外，我们的实验可能与人类的条件直接相关，其中声音在没有感觉输入的情况下被感知，例如周围性耳鸣。

DESCRIPTION (provided by applicant): Spontaneous activity in developing sensory systems has been shown to be important for the growth and survival of projection neurons and may help to refine and stabilize sensory maps in the brain. Recent in vivo studies indicate that bursts of action potentials occur in afferent spiral ganglion neurons prior to the onset of hearing; however the mechanisms responsible for generating this activity have not been determined. Our preliminary studies indicate that inner hair cells (IHCs) in the developing cochlea are periodically depolarized by ATP that is released spontaneously from neighboring supporting cells. These ATP-dependent depolarizations can trigger Ca2+ action potentials in IHCs, suggesting that extracellular ATP may be responsible for initiating activity in auditory nerve fibers. Here, we propose to test the hypothesis that `spontaneous' activity in primary afferent spiral ganglion neurons prior to the onset of hearing requires purinergic receptor activation. We will use cochlear explant cultures prepared from prehearing rats to characterize the patterns of spontaneous activity that occur in spiral ganglion neurons, and determine whether this activity is dependent on ATP receptors and requires gap junctions/hemichannels. In addition, we will examine the firing patterns of spiral ganglion neurons in vivo, by making extracellular recordings from these neurons in prehearing rats. To test whether the in vivo firing of spiral ganglion neurons is mediated by ATP, we will infuse P2 receptor antagonists into the cochlea while recording extracellular action potentials from these neurons. These experiments seek to define the patterns of activity carried by auditory nerve fibers during the prehearing period and determine if this activity is mediated by the release of ATP within the cochlea. Ultimately, the data gained from these mechanistic studies will enable us manipulate this activity in vivo to determine the specific role that activity plays in auditory system development. PUBLIC HEALTH RELEVANCE: This proposal seeks to determine the mechanisms responsible for initiating sensory-independent activity in auditory nerves before the onset of hearing. As our preliminary findings suggest that ATP release from supporting cells may play an important role in the initiation of this activity, these studies may yield new insight into how mutations in gap junctions and other supporting cell-associated genes result in deafness. Furthermore, our experiments may have direct relevance to human conditions where sound in perceived in the absence of sensory input, such as peripheral tinnitus.