A new research describes how the brains of mice are damaged by exposure to air pollution in early life.

The brain damage includes the enlargement of a part of the brain that is seen in humans who have autismand schizophrenia.

The study is published in the journal Environmental Health Perspectives.

As in autism and schizophrenia, the changes occurred predominately in males. The mice also performed poorly in tests of short-term memory, learning ability, and impulsivity¹.

The new findings are consistent with several recent studies that have shown a link between air pollution and autism in children.

Most notably², a 2013 study in JAMA Psychiatryreported that children who lived in areas with high levels of traffic-related air pollution during their first year of life were three times as likely to develop autism.

“Our findings add to the growing body of evidence that air pollution may play a role in autism, as well as in other neurodevelopmental disorders,” said Deborah Cory-Slechta, Ph.D., professor of environmental medicine at the University of Rochester and lead author of the study.

In three sets of experiments, Cory-Slechta and her colleagues exposed mice to levels of air pollution typically found in mid-sized US cities during rush hour.

The exposures were conducted during the first two weeks after birth, a critical time in the brain’s development. The mice were exposed to polluted air for four hours each day for two four-day periods.

In one group of mice, the brains were examined 24 hours after the final pollution exposure. In all of those mice, inflammation was rampant³ throughout the brain, and the lateral⁴ ventricles —chambers on each side of the brain that contain cerebrospinal fluid —were enlarged two to three times their normal size.

“When we looked closely at the ventricles, we could see that the white matter that normally surrounds them hadn’t fully⁵ developed,” said Cory-Slechta.

“It appears that inflammation had damaged those brain cells and prevented that region of the brain from developing, and the ventricles simply expanded to fill the space.”

The problems were also observed in a second group of mice 40 days after exposure and in another group 270 days after exposure, indicating that the damage to the brain was permanent.

Brains of mice in all three groups also had elevated levels of glutamate, a neurotransmitter, which is also seen in humans with autism and schizophrenia.

Most air pollution is made up mainly of carbon particles that are produced when fuel is burned by power plants, factories, and cars. For decades, research on the health effects of air pollution has focused on the part of the body where its effects are most obvious —the lungs.

That research began to show that different-sized particles produce different effects. Larger particles, the ones regulated by the Environmental Protection Agency (EPA), are actually the least harmful because they are coughed up and expelled.

But many researchers believe that smaller particles known as ultrafine particles —which are not regulated by the EPA —are more dangerous, because they are small enough to travel deep into the lungs and be absorbed into the bloodstream, where they can produce toxic⁶ effects throughout the body.

That assumption led Cory-Slechta to design a set of experiments that would show whether ultrafine particles have a damaging effect on the brain, and if so, to reveal the mechanism⁷ by which they inflict⁸ harm. The study is the first scientific work to do both.

“I think these findings are going to raise new questions about whether the current regulatory standards for air quality are sufficient to protect our children,” said Cory-Slechta.

一项新研究表明，老鼠若在幼年期长期接触污染大气，脑部可能会受损。

这种受损包括大脑某一部分变肿大，就人类而言，变肿大的部分常出现在自闭者与精神分裂患者脑中。

相关研究结果已发布在《环境健康透视》杂志上。

就自闭症和精神分裂而言，这种变化更多出现在雄性之中。此外，试验中雄性小鼠的短期记忆、学习能力和冲动性行为均有下降。

除本实验外，其他最近几项研究也表明大气污染可导致儿童自闭症。

最显著的是2013年《美国医学协会杂志:精神病学分册》上发表的一项研究，该研究显示儿童若在一岁多时生活在交通尾气污染严重地区，患上自闭症的概率是同龄儿童的三倍。

“随着调查的深入，我们搜集到的证据也越来越多，这些数据一致表明大气污染和自闭症之间存在必然联系，污染甚至还可能引发神经系统发育障碍，”罗切斯特大学环境医学教授德博拉•科里•斯彻塔解释道。

在三组试验中，斯彻塔与同事采集了美国二线城市交通高峰期的空气样本，并将老鼠置于其中。

科里•斯彻塔用出生仅两周的老鼠进行试验，此时正值其脑部发育的关键时期。试验期间，小鼠每天要呼吸污染的空气长达四个小时，为期两到四天，试验分为两期进行。

试验结束后，科里为第一组小鼠进行了长达二十四小时的脑部检查。所有小鼠的大脑和侧脑室均已严重发炎——左右脑的脑腔里都是脑脊髓液——小鼠的大脑增大两至三倍。

“我们仔细检查了小鼠的脑室，发现大脑的白质未完全发育”，科里•斯彻塔说道。

“我们观察发现炎症损害了小鼠的脑细胞，限制了大脑的发育，脑室不断扩张，占满了整个大脑。”

科里•斯彻塔还在试验后40天和270天分别测试了第二和第三组小鼠，发现大气污染对脑部造成的伤害是永久性的。

三组小鼠的脑内的谷氨酸水平也明显升高，谷氨酸是一种神经递质，如果人类脑部的谷氨酸水平过高，则会患上自闭症和精神分裂。

空气污染产生的主要原因是发电厂，工厂和汽车燃烧燃料后排放出的碳粒子。几十年来，在研究大气污染对健康的影响时，人们往往只关注病症最明显的部位——肺。

随着研究的深入，研究人员渐渐发现不同大小的碳颗粒对大脑的损害不同。大型碳颗粒受美国环保局监管，其实会被人体咳出或排出，危害最小。

但许多研究者认为那些小型碳颗粒，又叫做超微颗粒——不受美国环境保护局监管——其实危害更大，因为小型碳颗粒体积较小，可能会被吸入肺部或是融入血液，从而毒害人体。

为验证上述猜想，科里•斯彻塔设计了一系列实验，探究超微粒子是否会危害大脑，如果答案是肯定的，科里还将深入研究超微碳粒子是如何危害人体的。科里结合了这两方面来研究，开创了先河。

“现在的空气质量的监管标准能否保护我们的孩子呢？我觉得我的研究成果可能会起到警示的作用”，科里•斯彻塔说道。