The role of activity in auditory system development

描述(申请人提供)：感觉系统发育中的自发活动已被证明对投射神经元的生长和存活非常重要，并可能有助于完善和稳定大脑中的感觉图。最近的活体研究表明，在听力开始之前，传入螺旋神经节神经元就发生了动作电位的爆发；然而，产生这种活动的机制尚未确定。我们的初步研究表明，发育中的耳蜗内毛细胞(IHC)周期性地被邻近支持细胞自发释放的ATP去极化。这些依赖于ATP的去极化可以触发IHC中的Ca~(2+)动作电位，提示细胞外的ATP可能是启动听神经纤维活动的原因。在这里，我们建议检验一种假设，即初级传入螺旋神经节神经元在听力开始之前的自发活动需要嘌呤能受体的激活。我们将使用从预听大鼠制备的耳蜗外植体培养来表征螺旋神经节神经元中发生的自发活动的模式，并确定这种活动是否依赖于ATP受体，以及是否需要缝隙连接/半突触。此外，我们将通过对预听大鼠的螺旋神经节神经元进行细胞外记录，来研究体内螺旋神经节神经元的放电模式。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区，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力前期听神经纤维携带的活动模式，并确定这种活动是否由耳蜗内ATP的释放所调节。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一活动，以确定活动在听觉系统发育中所起的具体作用。公共卫生相关性：这项建议试图确定在听力开始之前启动听神经中非感官活动的机制。由于我们的初步发现表明，支持细胞的ATP释放可能在这种活动的启动中发挥重要作用，这些研究可能会对缝隙连接和其他支持细胞相关基因的突变如何导致耳聋提供新的见解。此外，我们的实验可能与在没有感觉输入的情况下感知声音的人类条件有直接关联，例如外周耳鸣。

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.