Leake Patricia A, Hradek Gary T, Chair Leila, Snyder Russell L
Epstein Hearing Research Laboratory, Department of Otolaryngology - Head and Neck Surgery, University of California San Francisco, San Francisco, California 94143-0526, USA.
J Comp Neurol. 2006 Jul 1;497(1):13-31. doi: 10.1002/cne.20968.
We previously examined the early postnatal maturation of the primary afferent auditory nerve projections from the cat cochlear spiral ganglion (SG) to the cochlear nucleus (CN). In normal kittens these projections exhibit clear cochleotopic organization before birth, but quantitative data showed that their topographic specificity is less precise in perinatal kittens than in adults. Normalized for CN size, projections to the anteroventral (AVCN), posteroventral (PVCN), and dorsal (DCN) subdivisions are all significantly broader in neonates than in adults. By 6-7 postnatal days, projections are proportionate to those of adults, suggesting that significant refinement occurs during the early postnatal period. The present study examined SG projections to the CN in adult cats deafened as neonates by ototoxic drug administration. The fundamental organization of the SG-to-CN projections into frequency band laminae is clearly evident despite severe auditory deprivation from birth. However, when normalized for the smaller CN size in deafened animals, projections are disproportionately broader than in controls; AVCN, PVCN, and DCN projections are 39, 26, and 48% broader, respectively, than predicted if they were precisely proportionate to projections in normal hearing animals. These findings suggest that normal auditory experience and neural activity are essential for the early postnatal development (or subsequent maintenance) of the topographic precision of SG-to-CN projections. After early deafness, the basic cochleotopic organization of the CN is established and maintained into adulthood, but the CN is severely reduced in size and the topographic specificity of primary afferent projections that underlies frequency resolution in the normal central auditory system is significantly degraded.
我们之前研究了从猫的耳蜗螺旋神经节（SG）到耳蜗核（CN）的初级传入听觉神经投射在出生后的早期成熟情况。在正常小猫中，这些投射在出生前就表现出清晰的耳蜗拓扑组织，但定量数据显示，它们的拓扑特异性在围产期小猫中不如在成年猫中精确。以CN大小进行归一化后，到前腹侧（AVCN）、后腹侧（PVCN）和背侧（DCN）亚区的投射在新生儿中都比在成年猫中显著更宽。到出生后6 - 7天，投射与成年猫的投射成比例，这表明在出生后的早期阶段发生了显著的精细化。本研究检查了成年猫在新生儿期因耳毒性药物给药而致聋后的SG到CN的投射。尽管从出生就严重缺乏听觉，但SG到CN投射到频带层的基本组织仍然清晰可见。然而，当以耳聋动物较小的CN大小进行归一化时，投射比对照组不成比例地更宽；AVCN、PVCN和DCN的投射分别比正常听力动物的投射精确成比例时预测的宽39%、26%和48%。这些发现表明，正常的听觉经验和神经活动对于SG到CN投射的拓扑精度在出生后的早期发育（或随后的维持）至关重要。早期耳聋后，CN的基本耳蜗拓扑组织在成年期得以建立和维持，但CN的大小严重减小，并且在正常中枢听觉系统中构成频率分辨率基础的初级传入投射的拓扑特异性显著降低。
