GRE Reading Comprehension: JiJing 352-GRE阅读机经352篇 - D27156HI268AO_5OK

In laboratories, healthy adult human brain neurons typically live no more than a few hours, making extensive research impossible. Furthermore, scientists' inability to reproduce healthy neurons has prevented the use of neurons in experimental treatments of severe neurological disorders. However, two researchers at the Johns Hopkins University School of Medicine have successfully maintained mature, human brain neurons in long-term cultures by using cells obtained during surgery on an 18-month-old victim of unilateral megalencephaly. The rare disorder, in which one side of the brain grows substantially larger than the other, occurs when neurons in the abnormal hemisphere undergo too many cell divisions before they mature. The neuronal imbalance in the brain of the infant caused seizures, prompting surgeons to remove the enlarged hemisphere – a treatment that has proven successful in similar cases. The researchers then took neurons from the excised brain matter and placed them in a blood-rich culture medium. After days, many of the cells had died, but a few continued to grow and divide. Nineteen months later, the team had subcultured colonies of neurons onto new culture plates more than 20 times, with no significant changes in cellular appearance or growth characteristics. Scientists still don't know what triggers the proliferation of neurons in unilateral megalencephaly. The neurons cultivated at Johns Hopkins – unlike those culled from tumors – are not cancerous, and accordingly are much more valuable as research tools. Finally, the experiment presents the possibility that such neurons could be used in experimental treatments that currently use fetal brain cells, sidestepping an uncomfortable ethical issue.