Auditory and visual dysfunction following lead exposure.
Auditory and visual dysfunction following lead exposure.
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作者：
D. Otto;D. Fox
在过去的十年中，人们对铅暴露对认知功能的影响进行了深入研究，但对铅暴露对感觉功能的影响却知之甚少。然而，视觉和/或听觉处理的细微损伤可能对学习产生深远的影响。本文的目的是回顾已知的铅暴露对视觉和听觉功能的影响，并确定相关的研究需求。特别是，铅暴露对儿童感觉功能的影响，尚未得到充分的研究，将讨论。来自人类和动物研究的证据表明，铅暴露会损害听觉功能。在发育和成熟的人和实验动物中，耳蜗神经和更多的中枢结构似乎都是优先敏感的。在中低水平的铅暴露中，听力阈值升高和脑干听觉诱发电位潜伏期增加已被报道。高剂量的铅使听神经动作电位阈值升高，引起耳蜗神经节段性脱髓鞘和轴突变性，但似乎对耳蜗的微音或结构没有影响。铅暴露影响视网膜和视觉皮层的发展和成熟的视觉系统。低至中等水平的发育性铅暴露会产生选择性的视杆缺陷，这可以通过电生理和行为技术来检测。稍高水平的铅暴露会影响视觉皮层。在大鼠中观察到，当血铅水平低于目前关注的20微克/分升时，会对视网膜功能产生广泛的功能和神经化学影响。大鼠、猴子和人类杆状体的结构、生物物理和光化学相似性证明了这些数据与儿科铅筛查的相关性。然而，到目前为止，还没有在铅暴露儿童中检查过杆状细胞介导的视觉功能。这些未被发现的感觉缺陷可能对儿童的运动和智力发展以及受影响的成年人的生活质量产生深远的影响。显然，有必要在儿童和工人中进行更广泛的感觉测试，以筛选铅引起的健康影响，并在动物模型中阐明铅神经毒性的机制。
The effects of lead exposure on cognitive function have been intensively studied during the past decade, but relatively little effort has been made to understand the impact on sensory function. Subtle impairments of visual and/or auditory processing, however, could have profound effects on learning. The objectives of this paper are to review what is known about the effects of lead exposure on visual and auditory function and to identify related research needs. In particular, the effects of lead exposure on sensory function in children, which have not been studied adequately, will be discussed. Evidence from human and animal studies reveal that lead exposure impairs auditory function. The cochlear nerve and more central structures appear to be preferentially sensitive in both developing and mature humans and experimental animals. Elevations in hearing thresholds and increased latencies of brainstem auditory evoked potential have been reported at low-moderate levels of lead exposure. Higher doses of lead increase the threshold of the auditory nerve action potential, produce segmental demyelination and axonal degeneration of the cochlear nerve, but appear to have no effect on cochlear microphonics or structure. Lead exposure affects both the retina and visual cortex of the developing and mature visual system. Low to moderate level developmental lead exposure produces selective rod deficits which can be detected with electrophysiological and behavioral techniques. At slightly higher levels of lead exposure the visual cortex is affected. A wide range of functional and neurochemical effects on retinal function occurring at blood lead levels below 20 micrograms/dl, the current level of concern, have been observed in rats. Structural, biophysical and photochemical similarities of rods in rats, monkeys and humans argue the relevance of this data for pediatric lead screening. To date, however, rod-mediated visual functions have not been examined in lead-exposed children. Undetected sensory deficits of these kinds may have profound impact on the motor and mental development of children as well as on the quality of life of affected adults. There is clearly a need for more extensive sensory testing in children and workers to screen for lead-induced health effects and in animal models to clarify the mechanisms of lead neurotoxicity.