Development & Connections of Cochlear Spiral Ganglion

这项拟议的研究解决了有关耳蜗发育的具体问题， 建立螺旋神经节投射到耳蜗核（CN）的拓扑结构。 细胞化学标记技术（NB和Dil）用于神经束示踪结合电生理 将采用记录和广泛的定量光和电子显微镜分析。我们最近 研究表明，从螺旋神经节基底节到CN各亚部的投射 在出生后的早期发育中经历了显著的精炼。投射到前腹侧 当对CN大小进行标准化时，新生儿的AVCN比成人宽50%以上， 这些神经元投射到背侧（DCN）和后腹侧（posteroventral）， （PVCN）的细分比成年人的细分宽30%。拟议实验的目标包括： 1)进一步研究妊娠晚期地形细化的时间和顺序的细节 和出生后早期发育的投影到CN的每个细分。2)检查投影 以确定其CN投射的成熟是否与基底到顶端平行 Corti器官的成熟。3)完成新生儿耳聋影响的定量研究 在成年后的严重听觉剥夺后检查CN预测的特异性。 4)确定CN预测是否正常发展或是否发生重大重组， 螺旋神经节在早期发育过程中产生的限制性病变的结果。5)以确定 CN投射的解剖学重构是否是频率选择性明显丧失的基础 由慢性脑内电刺激引起。6)为了探索正常的 通过检查自发活动的性质（如果有的话）， 螺旋神经节7)描述猫出生后发育的选定超微结构特征 Corti器官在特定的频率位置。拟议的实验将增加我们对 在发育中的听觉系统的信息处理机制的解剖框架，并将 解决关于关键期和可塑性的重要问题。此外，将在以下领域开展研究： 人工耳蜗植入对儿童的实际应用具有重要意义。

This proposed research addresses specific questions regarding the development of the cochlea and the establishment of the topographic organization of spiral ganglion projections to the cochlear nuclei (CN). Cytochemical labeling techniques (NB and Dil) for neuronal tract tracing combined with electrophysiological recording and extensive quantitative light and electron microscopic analyses will be employed. Our recent studies have shown that projections from basal sectors of the spiral ganglion to each subdivision of the CN undergo significant refinement during early postnatal development. Projections to the anteroventral subdivision (AVCN) are more than 50% broader in neonates than in adults when normalized for CN size, and the descending collaterals of these same neurons projecting to the dorsal (DCN) and posteroventral (PVCN) subdivisions are 30% broader than their adult counterparts. Goals of proposed experiments include: 1) To further investigate the details of timing and sequence of topographic refinement during late gestation and early postnatal development of the projections to each subdivision of the CN. 2) To examine projections from the apical cochlea to determine if maturation of its CN projections parallels the basal-to-apical maturation of the organ of Corti. 3) To complete quantitative studies of the effects of neonatal deafening upon the specificity of CN projections examined in adulthood after a lifetime of severe auditory deprivation. 4) To determine whether CN projections develop normally or if significant reorganization occurs as a consequence of restricted lesions of the spiral ganglion created during early development. 5) To determine whether anatomical remodeling of CN projections underlies the apparent loss of frequency selectivity induced by chronic intracochlear electrical stimulation. 6) To explore the mechanisms which underlie normal development of the auditory nerve projections by examining the nature of spontaneous activity (if any) in spiral ganglion. 7) To characterize selected ultrastructural features of postnatal development of the cat organ of Corti at specific frequency locations. The proposed experiments will increase our understanding of the anatomical framework for information processing mechanisms in the developing auditory system and will address important questions regarding critical periods and plasticity. In addition, studies to be conducted in deafened animals have practical implications regarding application of cochlear implants in children.