Leake P A, Snyder R L, Hradek G T, Rebscher S J
Department of Otolaryngology, University of California San Francisco 94143-0526, USA.
Hear Res. 1995 Jan;82(1):65-80. doi: 10.1016/0378-5955(94)00167-o.
This investigation examined the consequences of neonatal deafness and chronic electrical stimulation of the cochlea in the developing auditory system. Cats were bilaterally deafened by daily ototoxic drug administration for two weeks after birth. Electrical stimulation was initiated at 6-9 weeks of age and continued for up to 6 months, using monopolar round window electrodes that synchronously excited auditory neurons throughout the cochlea. Morphometric evaluation of the density of spiral ganglion cell somata within Rosenthal's canal demonstrated that chronic stimulation induced an increase of about 6% in neuronal survival. Although this difference was statistically significant, extracochlear stimulation in these cats was less effective in preventing neural degeneration than lower intensity, more restricted intracochlear stimulation that was shown in a previous study to induce an average increase of about 13% in neuronal survival. Electrophysiological recording experiments conducted in the inferior colliculus in these animals indicated that monopolar extracochlear stimulation can induce profound alterations in the spatial (frequency) selectivity of the auditory midbrain. On average, results were similar to those previously reported for bipolar intracochlear stimulation, showing about a two-fold expansion of the central representation of chronically stimulated electrodes. However, results with extracochlear stimulation showed much greater variability among individual animals. The results presented suggest that it is problematic to effect consistent 'whole' nerve stimulation using monopolar round window electrodes. Moreover, this mode of stimulation can induce profound functional alterations in the central nervous system and is substantially less effective in forestalling the degeneration of auditory neurons than intracochlear stimulation. Both these results contraindicate the implantation of such electrodes in young children for the purpose of maintaining the integrity of the auditory system for later application of a multichannel cochlear implant.
本研究探讨了新生期耳聋及对发育中的听觉系统进行慢性耳蜗电刺激的后果。在出生后两周内，每天给猫双侧注射耳毒性药物使其致聋。在6 - 9周龄开始电刺激，并持续长达6个月，使用单极圆窗电极同步激发整个耳蜗的听觉神经元。对罗森塔尔管内螺旋神经节细胞胞体密度进行形态学评估表明，慢性刺激使神经元存活率提高了约6%。虽然这一差异具有统计学意义，但与先前研究中显示能使神经元存活率平均提高约13%的较低强度、更局限的耳蜗内刺激相比，这些猫的耳蜗外刺激在预防神经退变方面效果较差。在这些动物的下丘进行的电生理记录实验表明，单极耳蜗外刺激可引起听觉中脑空间（频率）选择性的深刻改变。平均而言，结果与先前报道的双极耳蜗内刺激相似，显示慢性刺激电极的中枢表征扩大了约两倍。然而，耳蜗外刺激的结果在个体动物之间差异更大。所呈现的结果表明，使用单极圆窗电极实现一致的“全”神经刺激存在问题。此外，这种刺激方式可引起中枢神经系统的深刻功能改变，并且在防止听觉神经元退变方面比耳蜗内刺激效果要差得多。这两个结果均不支持为了维持听觉系统的完整性以便日后应用多通道人工耳蜗而在幼儿中植入此类电极。
