Moore D R, Hutchings M E, King A J, Kowalchuk N E
University Laboratory of Physiology, Oxford, United Kingdom.
J Neurosci. 1989 Apr;9(4):1213-22. doi: 10.1523/JNEUROSCI.09-04-01213.1989.
To examine the influence of acoustic experience on the development of the mammalian auditory brain stem, darkly pigmented ferrets were reared with a plug inserted in the right outer ear. The plugs were first inserted on postnatal day 23-34 and produced a variable, frequency-dependent attenuation of up to 60 dB. Between 3-15 months after the ear plug was begun, animals were prepared for physiological recording and injection of wheat germ agglutinin-HRP (WGA-HRP) in the left inferior colliculus (IC). The plug was removed and the condition of the right ear was assessed by pure-tone stimulation and recordings from neurons in the left IC. Neural audiograms for each animal showed a residual deficit in most cases. Following 24-60 hr survival, the animals were perfused and the right ear was examined. Brain-stem sections were reacted with tetramethylbenzidine. Outer and/or middle ear pathology was present in over half of the animals. However, the cochleas appeared to be normal and the spiral ganglion cells were normal by several quantitative criteria: number, area, and nucleolar eccentricity. The volume of each division of the cochlear nuclei (CN) and the areas of individual neurons in the anteroventral CN were the same on the right and left sides. The number of CN neurons retrogradely labeled from the left IC injection of WGA-HRP was found to be significantly increased in the left CN, relative to normal animals, when expressed as a ratio of the number labeled in the right CN. We conclude that the residual hearing loss in the previously plugged ears was predominantly or exclusively conductive. Neonatal, unilateral conductive hearing loss in the ferret does not lead to degeneration of the CN on the side of the loss, but it does lead to at least one rearrangement of auditory brain-stem connectivity. We suggest that the extent to which the brain stem is modified by early auditory deprivation is dependent on the type, degree, and symmetry of the hearing loss.
为研究声学经验对哺乳动物听觉脑干发育的影响，将深色雪貂饲养时在其右外耳插入耳塞。耳塞于出生后第23至34天首次插入，可产生高达60分贝的可变频率依赖性衰减。在开始佩戴耳塞3至15个月后，对动物进行生理记录准备，并在左侧下丘（IC）注射麦胚凝集素-HRP（WGA-HRP）。取下耳塞，通过纯音刺激和记录左侧IC中的神经元来评估右耳状况。多数情况下，每只动物的神经听力图显示有残余听力缺陷。在存活24至60小时后，对动物进行灌注并检查右耳。脑干切片用四甲基联苯胺反应。超过半数的动物存在外耳和/或中耳病变。然而，通过几个定量标准来看，耳蜗似乎正常，螺旋神经节细胞也正常：数量、面积和核仁偏心度。耳蜗核（CN）各部分的体积以及前腹侧CN中单个神经元的面积在左右两侧相同。当以右侧CN中标记的数量之比表示时，发现从左侧IC注射WGA-HRP逆行标记的CN神经元数量相对于正常动物在左侧CN中显著增加。我们得出结论，先前佩戴耳塞耳朵中的残余听力损失主要或完全是传导性的。雪貂新生儿期单侧传导性听力损失不会导致听力损失侧的CN退化，但确实会导致听觉脑干连接至少发生一种重排。我们认为，早期听觉剥夺对脑干的改变程度取决于听力损失的类型、程度和对称性。
