PHYSIOLOGICAL DEVELOPMENT OF THE EFFERENT SYSTEM

虽然人们对橄榄耳的生理学有很多了解 成年哺乳动物的反射，对其发育情况知之甚少 生理学。内侧橄榄蜗束的组织结构 (OCB)在耳蜗内的投射似乎是在出生后在 猫。在围产期的动物中，解剖学研究表明传出神经 仅投射到内毛细胞区域，与 成人的一些投射形成直接的轴体突触。传出 另一方面，外毛细胞区域的神经支配被延迟。 好几天了。因此，耳蜗神经支配被独特地组织起来 在围产期动物中，我们打算利用的一种情况 生理上的。成人型神经模式被认为是后天习得的 在出生后的头几周。在拟议的调查中， 将对橄榄耳蜗环的两个肢体进行神经生理学研究， 使用了多种方法。首先，声音诱发的反应 单独的传出纤维，记录在内耳道内， 将在猫的发育过程中进行检查，以确定这些细胞的成熟 神经元与初级传入神经元的发育或 更靠近嘴部的橄榄耳蜗区的发育是否延迟 神经元。此外，OCB将在 第四脑室底部，从而绕过听觉外周，以及 使我们能够检查OCB纤维的内在特性 发展。最后，分析了影响农业产业化经营发展的因素。 将通过检查以下疾病的后果来调查橄榄耳蜗环 OCB刺激和去传出对听神经反应的影响(个体 纤维和诱发电位)处于适当的发育阶段。这个 有待检验的总体假设是，橄榄耳耳蜗环是 猫在出生时还不成熟，某些反应特征，如 频率选择性，与频率的发展同步发展 以及第二组响应属性，例如 最大驱动放电率和穗列规律性变得成人化 在较长的产后期内的特征。全球的、长期的 拟议研究的目的是扩大我们对听觉的理解 在未成熟动物和成年动物中的功能，并为 未来的研究旨在关注早期感染的后果 潜在危险环境物质的暴露及其改善 先天听力异常。

Although a great deal is known about the physiology of the olivocochlear reflex in adult mammals, very little is known about its developmental physiology. The organization of the lateral an medial olivocochlear bundle (OCB) projections within the cochlea appears to develop postnatally in the cat. In perinatal animals, anatomical studies have shown that efferents project exclusively to the region of inner hair cells, where, unlike in adults, some projections form direct axosomatic synapses. Efferent innervation to the outer hair cell region, on the other hand, is delayed for several days. Consequently, cochlear innervation is uniquely organized in perinatal animals, a condition that we propose to exploit physiologically. Adultlike innervaion patterns are thought to be acquired during the first several postnatal weeks. In the proposed investigation, both limbs of the olivocochlear loop will be studied neurophysiologically, using a variety of methods. First, acoustically-evoked responses of individual efferent fibers, recorded within the internal auditory canal, will be examined in developing cats to determine if the maturation of these neurons coincides with the development of primary afferent neurons or whether development is delayed for the more rostrally-located olivocochlear neurons. Additionally, the OCB will be electrically stimulated at the floor of the fourth ventricle, thus bypassing the auditory periphery, and allowing us to examine the intrinsic properties of OCB fibers during development. Lastly, factors influencing the development of the olivocochlear circuit will be investigated by examining the consequences of OCB stimulation and deefferentation on auditory nerve responses (individual fibers and evoked potentials) at appropriate developmental stages. The overall hypothesis to be tested is that the olivocochlear circuit is immature at birth in the cat and that certain response features, such as frequency selectivity, develop coincidently with the development of the auditory periphery and that a second set of response properties, such as maximum driven discharge rate and spike train regularity acquire adultlike characteristics over an extended postnatal period. The global, long-term purpose of the proposed research is to extend our understanding of auditory function in both immature and adult animals, and to provide a basis for future research aimed at concerns regarding the consequences of early exposure to potentially hazardous environmental agents and the amelioration of congenital hearing anomalies.