PDF(Pubmed)
Abstract：
UNASSIGNED: Age-related hearing difficulties have a complex etiology that includes degenerative processes in the sensory cochlea. The cochlea comprises the start of the afferent, ascending auditory pathway, but also receives efferent feedback innervation by two separate populations of brainstem neurons: the medial olivocochlear and lateral olivocochlear pathways, innervating the outer hair cells and auditory-nerve fibers synapsing on inner hair cells, respectively. Efferents are believed to improve hearing under difficult conditions, such as high background noise. Here, we compare olivocochlear efferent innervation density along the tonotopic axis in young-adult and aged gerbils (at ~50% of their maximum lifespan potential), a classic animal model for age-related hearing loss.
UNASSIGNED: Efferent synaptic terminals and sensory hair cells were labeled immunohistochemically with anti-synaptotagmin and anti-myosin VIIa, respectively. Numbers of hair cells, numbers of efferent terminals, and the efferent innervation area were quantified at seven tonotopic locations along the organ of Corti.
UNASSIGNED: The tonotopic distribution of olivocochlear innervation in the gerbil was similar to that previously shown for other species, with a slight apical cochlear bias in presumed lateral olivocochlear innervation (inner-hair-cell region), and a broad mid-cochlear peak for presumed medial olivocochlear innervation (outer-hair-cell region). We found significant, age-related declines in overall efferent innervation to both the inner-hair-cell and the outer-hair-cell region. However, when accounting for the age-related losses in efferent target structures, the innervation density of surviving elements proved unchanged in the inner-hair-cell region. For outer hair cells, a pronounced increase of orphaned outer hair cells, i.e., lacking efferent innervation, was observed. Surviving outer hair cells that were still efferently innervated retained a nearly normal innervation.
UNASSIGNED: A comparison across species suggests a basic aging scenario where outer hair cells, type-I afferents, and the efferents associated with them, steadily die away with advancing age, but leave the surviving cochlear circuitry largely intact until an advanced age, beyond 50% of a species\' maximum lifespan potential. In the outer-hair-cell region, MOC degeneration may precede outer-hair-cell death, leaving a putatively transient population of orphaned outer hair cells that are no longer under efferent control.
UNASSIGNED: Efferent synaptic terminals and sensory hair cells were labeled immunohistochemically with anti-synaptotagmin and anti-myosin VIIa, respectively. Numbers of hair cells, numbers of efferent terminals, and the efferent innervation area were quantified at seven tonotopic locations along the organ of Corti.
UNASSIGNED: The tonotopic distribution of olivocochlear innervation in the gerbil was similar to that previously shown for other species, with a slight apical cochlear bias in presumed lateral olivocochlear innervation (inner-hair-cell region), and a broad mid-cochlear peak for presumed medial olivocochlear innervation (outer-hair-cell region). We found significant, age-related declines in overall efferent innervation to both the inner-hair-cell and the outer-hair-cell region. However, when accounting for the age-related losses in efferent target structures, the innervation density of surviving elements proved unchanged in the inner-hair-cell region. For outer hair cells, a pronounced increase of orphaned outer hair cells, i.e., lacking efferent innervation, was observed. Surviving outer hair cells that were still efferently innervated retained a nearly normal innervation.
UNASSIGNED: A comparison across species suggests a basic aging scenario where outer hair cells, type-I afferents, and the efferents associated with them, steadily die away with advancing age, but leave the surviving cochlear circuitry largely intact until an advanced age, beyond 50% of a species\' maximum lifespan potential. In the outer-hair-cell region, MOC degeneration may precede outer-hair-cell death, leaving a putatively transient population of orphaned outer hair cells that are no longer under efferent control.
摘要：
■年龄相关的听力困难具有复杂的病因，包括感觉耳蜗的退行性过程。耳蜗包括传入的开始，上行听觉通路，但也接受传出反馈神经支配的两个独立群体的脑干神经元：内侧耳蜗和外侧耳蜗途径，支配外毛细胞和听觉神经纤维在内毛细胞上突触，分别。人们认为，在困难的条件下，会改善听力，例如高背景噪声。这里,我们比较了年轻成年沙鼠和老年沙鼠沿音调轴的橄榄耳蜗传出神经支配密度（约为其最大寿命潜力的50％），与年龄相关的听力损失的经典动物模型。
■用抗突触蛋白和抗肌球蛋白VIIa免疫组织化学标记传入突触末端和感觉毛细胞，分别。毛细胞的数量，传出端子的数量，并在Corti器官的七个位置对传出神经支配区域进行了量化。
■沙鼠中人工耳蜗神经支配的位素分布与先前显示的其他物种相似，假定的外侧耳蜗神经支配（内毛细胞区域）有轻微的顶端耳蜗偏向，和假定的内侧橄榄耳蜗神经支配的宽中耳蜗峰（外毛细胞区域）。我们发现有意义，与年龄相关的内毛细胞和外毛细胞区域的总体传出神经支配下降。然而,在计算传出目标结构中与年龄相关的损失时，在内毛细胞区域中存活元素的神经支配密度没有变化。对于外毛细胞，孤儿的外毛细胞明显增加，即，缺乏传出神经支配，被观察到。仍然受到神经支配的存活外毛细胞保留了几乎正常的神经支配。
■跨物种的比较表明了一种基本的衰老情况，即外部毛细胞，I型传入，以及与之相关的传出者，随着年龄的增长稳步消亡，但是保留幸存的耳蜗电路基本完好无损，直到高龄，超过物种最大寿命潜力的50%。在外毛细胞区域,MOC变性可能先于外毛细胞死亡，留下假定的瞬时孤儿外毛细胞群，不再受到传出控制。
■用抗突触蛋白和抗肌球蛋白VIIa免疫组织化学标记传入突触末端和感觉毛细胞，分别。毛细胞的数量，传出端子的数量，并在Corti器官的七个位置对传出神经支配区域进行了量化。
■沙鼠中人工耳蜗神经支配的位素分布与先前显示的其他物种相似，假定的外侧耳蜗神经支配（内毛细胞区域）有轻微的顶端耳蜗偏向，和假定的内侧橄榄耳蜗神经支配的宽中耳蜗峰（外毛细胞区域）。我们发现有意义，与年龄相关的内毛细胞和外毛细胞区域的总体传出神经支配下降。然而,在计算传出目标结构中与年龄相关的损失时，在内毛细胞区域中存活元素的神经支配密度没有变化。对于外毛细胞，孤儿的外毛细胞明显增加，即，缺乏传出神经支配，被观察到。仍然受到神经支配的存活外毛细胞保留了几乎正常的神经支配。
■跨物种的比较表明了一种基本的衰老情况，即外部毛细胞，I型传入，以及与之相关的传出者，随着年龄的增长稳步消亡，但是保留幸存的耳蜗电路基本完好无损，直到高龄，超过物种最大寿命潜力的50%。在外毛细胞区域,MOC变性可能先于外毛细胞死亡，留下假定的瞬时孤儿外毛细胞群，不再受到传出控制。
