Washington: In what could be called a key breakthrough, scientists have found that tiny blood vessels in brain spit to survive.
A team at Northwestern University has, in fact, discovered that capillaries have a unique method of expelling debris, such as blood clots, cholesterol or calcium plaque, which blocks the flow of essential nutrients to brain cells.
The capillaries spit out the blockage by growing a membrane that envelopes the obstruction and then shoves it out of the blood vessel. And, this critical process is 30 to 50 percent slower in an ageing brain and likely results in the death of more capillaries, say the scientists.
"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.
Their recovery is much slower," said lead scientist Prof Jaime Grutzendler.
The findings, published in the `Nature` journal have been based on a study of mice.
Researchers 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 little was known about how capillaries clear blockages.
The Northwestern study first demonstrated that enzymes and blood pressure aren`t efficient at clearing capillary clots within the critical 24 to 48 hours. Those mechanisms work half the time and only when blood clots are involved, not other types of debris, particularly cholesterol, which is difficult to dissolve.
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 travelled 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.
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 scientists also found that the ability to move the blockage out of the blood vessel diminished with age.
"The reduced efficiency of this protective mechanism in the older brain and its effect on the function of nerve cells in the brain may significantly contribute to age-related cognitive decline," said team member Suzana Petanceska.