In laboratories, healthy adult human brain neurons typically live no m

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 21 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.

1. It can be inferred from the passage that neurons culled from the brain of a victim of unilateral megalencephaly

A) have only been successfully duplicated at the Johns Hopkins University School of Medicine
B) are more valuable to those researching neurological disorders than are those taken from tumors
C) breed at a rate sufficient to develop into a mature cerebral cortex
D) are of limited scientific value to the student of neuropsychology
E) will experience significant cellular changes as they grow and divide


2. The passage supplies information to answer which of the following questions?

A) How old is the average unilateral megalencephaly patient?
B) Can fetal brain cells be used to treat unilateral megalencephaly?
C) Have scientists found a way to allow cells from victims of unilateral megalencephaly to exist outside of the body?
D) How long can neurons culled from tumors be sustained outside the body?
E) Will scientists find further experimental uses for neurons culled from unilateral megalencephaly victims?


3. According to the passage, which of the following characteristics prove problematic for researchers working with mature brain cells?

I. The cells live only a very short time outside the human body.
II. The cells do not continue to undergo division.
III. Their study of these cells has sparked a heated ethical debate.

A) I only
B) I and II only
C) I and III only
D) II and III only
E) I, II, and III


4. It can be inferred from the passage that the removal of a hemisphere of the brain

A. will allow researchers to expand their knowledge of neurological workings
B. is necessary to cure unilateral megalencephaly
C. is a viable medical procedure in some cases
D. is usually performed on infants who suffer from unilateral megalencephaly
E. is a rare procedure that is performed as a last resort


5. According to the passage, which of the following is an advantage of conducting research using neurons culled from victims of unilateral megalencephaly?

A. Upon reaching maturity, neurons no longer divide.
B. Neurons taken from tumors in the central nervous system are cancerous.
C. Scientists know what triggers the proliferation of neurons in megalencephaly.
D. Normal mature neurons grow at a rate that complicates research.
E. the use of these cells allows scientists to avoid the ethical debate surrounding the use of neural fetal tissue.


6. The passage suggests that brain cells from a patient suffering from unilateral megalencephaly differ from normal mature brain cells because they

A. continue to divide after they are removed from the body
B. can live only in a blood-rich culture medium
C. are often cancerous
D. respond to brain chemicals called neurotransmitters
E. reproduce at an accelerated pace before they mature


7. It can be inferred that typical mature human brain neurons

A. are influenced by their own secretions
B. manufacture a variety of chemicals
C. continue to live in cultures for up to 21 days
D. cannot live for a full day outside of the body
E. reproduce unilaterally, rather than bilaterally