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Breaching the Blood Brain Barrier
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20653 |
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Section : |
NATURAL SCIENCE
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| Issue
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10 / 1992 |
2,378 Words |
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Malorye Allison
Malorye Allison is a free-lance writer based in Boston. |
Many promising drugs that might destroy brain tumors, cure infections such as meningitis, and possibly prevent nuero-degenerative diseases like Alzheimer's cannot even be tried today. The reason for this frustrating situation is that the same physiological shield that keeps the brain free of most unwanted visitors, such as viruses and other pathogens, also blocks certain types of drugs.
So how do you breach a barrier that nature has erected with the express purpose of protecting one of its most remarkable achievements? The body has its own ways of delivering vital substances such as glucose to the brain, and some pathogens use trickery to slip through. Scientists are hoping to use similar means to get drugs in.
Finding such avenues is a complex task, however. This "barrier" is not an entity that surrounds its protégé; rather it is a quality of the blood vessels in the brain, and so it infiltrates the brain, winding through every part of it in a seemingly endless tangle. In other parts of the body, the tiny capillary veins are relatively porous and act as a gateway, helping tissues exchange vital nutrients and wastes and wastes with the blood. The brain, however, is more exclusive: Only certain substances are admitted, and finding out how this is achieved is a major part of finding ways around it.
Confounding Questions
Mystery and confusion have cloaked the blood-brain barrier since it was first discovered. In 1885, renowned German scientist Paul Ehrlich was intrigued to find that when he injected a dye called Evan's blue into an animal's bloodstream, every tissue turned blue except the brain. "This was puzzling," explains Dr. Thomas Reese, director of the Neurobiology Division at the National Institute of Health. "People wondered how the brain could be receiving nourishment if the blood wasn't delivering it."
Researchers later found that molecules smaller than the particles in Evan's blue could cross into brain tissue, and that not all parts of the brain are so protected, particularly the hypothalamus and related regions. But what keeps most things out of the brain? Initially, some researchers thought the fingerlike projections of brain cells called glia were forming a seal around the tiny blood vessels. But when it was shown that glia leaked, that theory sink.
Then, in the late 1960s, Dr. Reese and several colleagues did a series of groundbreaking
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