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Brainy ties that bind.

Brainy ties that bind

An understanding of the workings ofthe blood-brain barrier -- so miserly about what passes from the blood to the brain -- has been sought by scientists for more than a century. Nearly 20 years ago, tight junctions were described between the endothelial cells of cerebral capillaries. Subsequent experiments showed that the ability of those cells to build the barrier is not intrinsic in endothelial cells, but is instead induced by their presence in the nervous system. Now, there is new evidence identifying which brain cells provide the signal to "git tight."

One specialized brain cell, the astrocyte,has long "feet" that wrap around capillaries and is thought to be active in the cross-membrane transport of certain substances, including potassium. But astrocytes apparently stimulate junction formation in endothelial cells as well. British scientists Robert C. Janzer and Martin C. Raff of University College London report in the Jan. 15 NATURE that the astrocytes are responsible for "including blood-brain barrier properties" in the endothelial cells.

Using cells grown on the surface ofthe iris in rats, as well as on the membranes of chick embryos, Janzer and Raff found that the "tissue lumps" formed by astrocytes -- which after several days were ingrown with blood vessels made up of endothelial cells -- did not absorb blue dye injected into the animals' circulatory systems.

As pointed out in an accompanyingarticle by N. Joan Abbott of Kings College London, evidence from this and other studies suggests that the inducing signal is a diffusible substance, secreted by some population of astrocytes. Abbott notes that the Janzer-Raff discovery does not answer all the questions: For instance, in some non-mammalian brains and in certain areas of the mammalian brain, the barrier is not always at the endothelial layer.
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Title Annotation:blood-brain barrier
Author:Edwards, Diane D.
Publication:Science News
Date:Jan 31, 1987
Words:290
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