Excitability and synaptic function of type II cochlear afferents

描述（由申请人提供）：这是一项旨在确定哺乳动物耳蜗至今神秘的II型传入神经功能特性的建议。虽然只包括一小部分（5-10%）的所有耳蜗传入，其独特的arborization外毛细胞，和终止模式的听觉脑干强烈暗示功能的作用，完全不同于I型传入。有限的数据表明，第二类传入有一个非常高的听觉阈值，也许信号只有创伤或痛苦的声音水平。进一步扩展到躯体疼痛纤维的类比，II型传入神经被耳蜗创伤期间可以释放的ATP激活，因为它在受损的皮肤中。该项目将涉及从离体耳蜗段中的II型传入的千兆欧姆密封细胞内记录，以表征II型传入的兴奋性和突触功能。将确定基本膜特性、动作电位阈值和起始位点以及突触输入的大小和分布。量子分析将确定外毛细胞突触强度。与记录的纤维相关的突触前和突触后结构将被免疫标记。这些数据将被纳入解剖学上正确的房室模型，以获得激活II型传入神经所需的声刺激的估计值。为了进一步探索耳蜗创伤中可能的作用，将在因大声和/或暴露于耳毒素而受损的耳蜗中进行II型记录。 听力损失会导致听觉过敏和耳鸣的幻觉。与周围致敏和“幻肢痛”的类比提示与躯体神经病相似。II型传入的功能作用的描述增加了重要的，长期缺失的信息耳蜗功能，将增强听觉发病机制的理论，并可能提供新的治疗目标。

DESCRIPTION (provided by applicant): This is a proposal to determine the functional properties of till-now-mysterious type II afferents of the mammalian cochlea. Although comprising only a small fraction (5-10%) of all cochlear afferents, their unique arborization to outer hair cells, and termination pattern in the auditory brainstem strongly imply a functional role quite distinct from that of the type I afferents. Limited data suggest that type II afferents have a very high acoustic threshold, perhaps signaling only traumatic or painful levels of sound. Further extending an analogy to somatic pain fibers, type II afferents are activated by ATP that can be released during cochlear trauma, as it is in damaged skin. This project will involve giga-ohm-seal intracellular recording from type II afferents in cochlear segments ex vivo to characterize the excitability and synaptic function of type II afferents. Basic membrane properties, action potential threshold and initiation site, and the size and distribution of synaptic inputs will be determined. Quantal analysis will determine outer hair cell synaptic strength. Pre- and postsynaptic structures associated with recorded fibers will be immunolabeled posthoc. These data will be incorporated into an anatomically-correct, compartmental model to obtain an estimate of the acoustic stimulus required to activate the type II afferent. To explore further a possible role in cochlear trauma, type II recordings will be made in cochleae that have been damaged by loud sound and/or exposure to ototoxins. Hearing loss can lead to hyperacusis and the phantom percept of tinnitus. The analogy to peripheral sensitization and 'phantom limb pain' prompts parallels with somatic neuropathy. Delineation of the functional role of type II afferents adds essential, long-missing information on cochlear function that will enhance theories of auditory pathogenesis, and may provide new therapeutic targets.