Spitting debris helps brain’s tiny blood vessels survive

June 5th, 2010 - 4:53 pm ICT by IANS  

Washington, June 5 (IANS) Capillaries have a unique method of ejecting debris, such as blood clots, cholesterol or calcium plaque, that blocks supply of vital nutrients to brain cells.
The facts have been revealed by a new study at Northwestern University’s (NU) Feinberg School of Medicine (FSM).

The capillaries spit out the blockage by growing a membrane that envelopes the obstruction and then pushes it out of the blood vessel.

Scientists also found this critical process is 30 to 50 percent slower in an aging brain and likely results in the death of more capillaries.

“The slowdown may be a factor in age-related cognitive decline and may also explain why elderly patients who get strokes do not recover as well as younger patients,” said Jaime Grutzendler, study co-author and principal investigator and assistant professor of Neurology and Physiology at FSM.

Scientists have long understood how large blood vessels clear blockages: blood pressure pushes against the clot and may eventually break it down and flush it away, or clot busting enzymes rush to the scene to dissolve a blockage.

But very little was previously known about how capillaries clear blockages. The study first demonstrated that enzymes and blood pressure aren’t efficient at clearing capillary clots.

Those mechanisms only work half the time and only when blood clots are involved, not other types of debris, particularly cholesterol, which is difficult to dissolve.

“So what happens to the blood vessels that that aren’t cleared out?” asked Grutzendler and colleagues. “Do they die, or does some other mechanism take over?”

To find out, they created micro-clots, tagged them with a red fluorescent substance and infused them into the carotid arteries of mice.

Using a multiphoton microscope, the team examined the brains of live mice at various time intervals as clots traveled into the capillaries.

Surprisingly, they discovered that the blood vessel cells next to the blockage grew a membrane that completely enveloped the debris.

Then the original wall of the blood vessel opened up and spit the debris into the brain tissue, rendering it harmless, said an NU release.

The envelope covering the clot became the new vessel wall. This resulted in complete restoration of blood flow and salvaging of the tiny vessel and surrounding brain cells.

The researchers also found that the ability to move the blockage out of the blood vessel diminished with age. Young mice (age 4 months) were able to clear blockages more quickly and thoroughly than older mice (age 22 months).

The findings were published in May 27 issue of Nature.

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