Aged Middle Ear

随着年龄增长而丧失听力是一种众所周知的现象，叫做老年性耳聋。从历史上和正确的角度来看，老年性耳聋很大程度上归因于毛细胞和初级神经元的退化，原因不明，尽管可能是遗传原因。该建议认为，老年人的听力损失也可能是由中耳传导装置的年龄相关变化引起的。人类中耳功能与年龄相关的变化的证据是模棱两可的。这很可能是由于传导性听力损失评估方法的局限性，而不是其他原因。然而，明确的证据表明，人类和动物中耳的传导装置都发生了结构变化。本研究的目的是建立一个动物模型，证明衰老对中耳结构和功能方面的影响。这样的模型将被用来详细描述这些中耳变化对听力的影响。这一目的是通过一系列的实验来评估青年和老年大鼠中耳的结构和功能。比较开始于使用光学和透射电子显微镜对这两个年龄组的鼓膜进行仔细的形态学评估。接下来，采用免疫组织化学方法鉴定与鼓膜相关的细胞外基质蛋白，并寻找两个年龄组之间的差异。然后，采用激光干涉测量法测量两个年龄组的鼓膜速度传递函数。这个函数描述了声音振动传播的频率依赖。最后，使用听觉脑系统反应技术来确定老年大鼠老年性耳聋的传导成分。每项研究都有特定的假设，预测老年大鼠的变化反映了声音传导的普遍恶化。这些实验可能揭示了迄今为止未被认识到的老年人听力损失的组成部分。

Loss of hearing with aging is a well known phenomenon called presbycusis. Presbycusis, historically and correctly, is largely attributed to hair cell and primary neurons degeneration from unknown, though probably genetic, causes. This proposal argues that hearing loss in the elderly may also arise from age-related changes in the conductive apparatus of the middle ear. The evidence for age-related changes in the human middle-ear function is equivocal. This is most likely due to limitations in the way conductive hearing loss is assessed rather than anything else. Nevertheless, clear evidence can be found for structural changes in the conductive apparatus of both the human and animal middle ear. The aim of the present research is to develop an animal model that demonstrates the effects of aging on the structural and functional aspects of the middle ear. Such a model would then be employed to detail the consequences of these middle-ear changes on hearing. This aim is realized in a series of experiments hat evaluate structure and function in the young adult and aged middle-ear of the rat. The comparison begins with i careful morphological assessment of the tympanic membrane using light and transmission electron microscopy in these two age groups. Next, immunohistochemistry is employed to identify extracellular matrix proteins associated with the tympanic membrane and differences are sought between the two age groups. Then, laser interferometry is used to measure the tympanic membrane velocity transfer function in the two age groups. This function describes the frequency dependent transmission of sound vibration. Finally, Auditory Bralnstem Reponse techniques are used to ascertain the conductive component to the presbycusis seen in the aged rat. Hypotheses specific to each of these studies predict changes in the older rats reflecting a general deterioration in sound conduction. These experiments may reveal a heretofore unrecognized component of the hearing loss seen in the elderly population.