Repeated TTS exposures in monkeys: alterations in hearing, cochlear structure, and single-unit thresholds.
Repeated TTS exposures in monkeys: alterations in hearing, cochlear structure, and single-unit thresholds.
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DOI：
10.1121/1.394503
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发表时间：
1987-05
期刊：
影响因子：
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通讯作者：
B. Lonsbury-Martin;G. Martin;B. Bohne
中科院分区：
文献类型：
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作者：
B. Lonsbury-Martin;G. Martin;B. Bohne
大量研究过量声音对听力影响的研究结果表明，噪声引起的听力损失的行为、生理和组织学指标之间的一致性可能显著依赖于特定措施的敏感性。最近的研究表明，单一听觉神经元在短暂暴露于纯音后的反应发生了显着变化，这表明单一单位的活动可能是对Corti感觉细胞器官生理损害的敏感指标。此外，神经反应性变化的长期性质表明，每一次临时性阈值漂移(TTS)事件都可能对耳朵造成损害，最终导致可测量的永久性阈值漂移(PTS)。这一含义的合乎逻辑的延伸是这样一种提议，即反复发作TTS首先会影响单位阈值，这种损害最终将表现为PTS。对这一概念的测试是通过让猴子反复接触短暂的TTS声音长达数月来进行的。在每次TTS诱导之前和之后使用反应时任务监测行为阈值。两名受试者参加了18个月的暴露会议，而其余的猴子则暴露在相同的刺激下6个月。在行为学测试结束时，准备从耳蜗核的单个细胞进行慢性记录。记录期结束后，准备耳蜗，作为塑料植入的整体支架进行检查。制作耳蜗管平面标本，确定耳蜗管对Corti器和有髓神经纤维的损伤位置和程度。在接受6个月的声音暴露经验的猴子中，没有注意到行为阈值的升高，而对于两个暴露在18个月的受试者，在暴露的最后几个月，显著的高频听力损失变得明显。对于受损的耳朵，同侧耳蜗核单位的特征频率(CFs)升高，特征频率(CFs)对应于行为阈值移位的频率区域。在暴露6个月的动物中，高频CFS单位的阈值也显示出敏感度的下降。对患有永久性听力损失的猴子的耳蜗组织学检查发现，Corti器官的高频区域也受到了相应的损害。暴露6个月的猴子，仅表现出单位阈值的升高，也有高频病变。
The findings of a number of studies investigating the effects of excessive sound on hearing have indicated that the correspondence between behavioral, physiological, and histological measures of noise-induced hearing loss may be markedly dependent upon the sensitivity of the particular measure. Recent studies demonstrating significant changes in the responses of single auditory neurons following brief exposures to pure tones suggest that single-unit activity may be a sensitive indicator of physiological insult to the organ of Corti's sensory cells. In addition, the long-lasting nature of the changes in neural responsiveness suggests that each temporary threshold shift (TTS) episode may produce an increment of damage to the ear that eventually contributes to a measurable permanent threshold shift (PTS). A logical extension of this implication is the proposal that repeated episodes of TTS would first affect single-unit thresholds, and that such damage would eventually manifest itself as PTS. A test of this notion was performed by repeatedly exposing monkeys to short-lasting TTS sounds for many months. Behavioral thresholds were monitored using a reaction-time task before and after each inducement of TTS. Two subjects participated in exposure sessions for 18 months, while the remaining monkey was exposed to identical stimuli for 6 months. At the end of behavioral testing, the monkeys were prepared for chronic recording from single cells of the cochlear nucleus. Following the recording period, cochleas were prepared for examination as plastic-embedded whole mounts. Flat preparations of the cochlear duct were made and the position and extent of damage to the organ of Corti and myelinated nerve fibers were determined. No elevations in behavioral threshold were noted for the monkey receiving 6 months of sound-exposure experience, while for both subjects exposed for 18 months, a significant high-frequency hearing loss became apparent during the final months of exposure. For damaged ears, the thresholds of ipsilateral cochlear nucleus units were elevated for characteristic frequencies (CFs) corresponding to the frequency regions where behavioral thresholds were shifted. Thresholds for units with high-frequency CFs in the animal exposed for 6 months also demonstrated a loss in sensitivity. Histological examination of the cochleas of monkeys with permanent hearing losses revealed corresponding damage to the high-frequency region of the organ of Corti. The monkey exposed for 6 months, which demonstrated only elevated unit thresholds, also had high-frequency lesions.(ABSTRACT TRUNCATED AT 400 WORDS)