Bottleneck in blood supply makes brain vulnerable to strokes

Jan 04, 2007

A team of University of California, San Diego physicists and neuroscientists has discovered a bottleneck in the network of blood vessels in the brain that makes it vulnerable to strokes. The finding may explain the origin of the puzzling damage to the brain's gray matter often detected in brain scans, especially among the elderly.

In the study, published this week in the journal Proceedings of the National Academy of Sciences, the researchers used a laser technique they developed to precisely monitor changes in blood flow resulting from an induced blockage in a tiny artery, or arteriole, in the brains of anesthetized rats. They found that the penetrating arterioles, which connect the blood vessels on the brain's surface with deeper blood vessels, are a vulnerable link in the network.

"The blood vessels on the surface of the brain are like a collection of city streets that provide multiple paths to get somewhere," explained David Kleinfeld, a professor of physics at UCSD, who led the team. "If one of the vessels is blocked, blood flow quickly rearranges itself. On the other hand, the penetrating arterioles are more like freeways. When blocked, the blood flow is stopped or slowed significantly in a large region round the clot."

The obstruction of blood flow resulted in damage to the surrounding brain area, which the researchers report resembled damage seen in the brains of humans and thought to be the result of "silent strokes." Silent strokes have attracted attention recently because magnetic resonance imaging has made it possible to follow changes in the brains of individuals as they age. MRI scans have revealed that, over time, small holes accumulate in the gray matter of many patients, including those who have no obvious behavioral signs of a stroke.

The researchers say their results support the hypothesis, made by clinicians, that the penetrating arterioles may be the location of small strokes that cause the death of sections of brain tissue in humans. The accumulation of damage may lead to memory loss, and may be a risk factor for having a larger stroke, according to Pat Lyden, a professor of neurosciences at UCSD's School of Medicine and head of the UCSD Stroke Center.

"This damage is an enormous problem," said Lyden, who collaborated with Kleinfeld on the study. "We think it is part of the dementia picture in Alzheimer's and non-Alzheimer's patients. But until now, we had no insight into the mechanism of the damage, and understanding the mechanism is the first step toward understanding how to prevent it."

To determine what happens in the brain during a stroke, the researchers created a tiny clot in a blood vessel in the brain of an anesthetized rat. They used focused laser light to excite a dye they had injected into the bloodstream. A chemical reaction of the excited dye "nicked" the blood vessel at the target location and triggered the natural clotting response.

"The technique creates a clot while generating very little collateral damage," said Beth Friedman, an associate project scientist working with Lyden in neurosciences and a contributing author on the paper. "Then we can study blood flow changes to understand what is happening in the brain in real time."

Before and after the formation of the clot, the researchers tracked the movements of red blood cells using two-photon fluorescence microscopy. Two-photon fluorescence microscopy is a powerful imaging tool that uses brief (less than one-trillionth of a second) laser pulses to peer below the surface of the brain.

In contrast to a previous study, in which the team showed there was very little disruption in blood flow when a clot formed in the blood vessels on the surface of the brain, a blockage in the penetrating arterioles had a significant effect. The flow of red blood cells was reduced far downstream of the blockage. Because blood flow cannot simply take alternate routes to compensate for the blockage, the penetrating arterioles are a bottleneck in the blood supply to gray matter.

"In this study, we took advantage of being able to see into individual capillaries in brain tissue," explained Nozomi Nishimura, who was a graduate student working with Kleinfeld in physics at the time of the study. "It is the capillaries, the smallest blood vessels, that provide the brain cells with oxygen and nutrients. So we were able to measure the dynamics of blood flow where it really matters to nerve cells."

Source: University of California - San Diego

Explore further: US scientists make embryonic stem cells from adult skin

add to favorites email to friend print save as pdf

Related Stories

Pets and anesthesia

Mar 21, 2014

Have you been avoiding getting your pet regular dental care? You're not alone. Most pet owners understand that in animals—just as in people—good oral health is conducive to overall well-being, says Gillian Fraser, V00, ...

Scientists identify a key to body's use of free calcium

Jan 23, 2014

Scientists at Johns Hopkins report they have figured out a key step in how "free" calcium—the kind not contained in bones—is managed in the body, a finding that could aid in the development of new treatments for a variety ...

Recommended for you

Leeches help save woman's ear after pit bull mauling

Apr 18, 2014

(HealthDay)—A pit bull attack in July 2013 left a 19-year-old woman with her left ear ripped from her head, leaving an open wound. After preserving the ear, the surgical team started with a reconnection ...

New pain relief targets discovered

Apr 17, 2014

Scientists have identified new pain relief targets that could be used to provide relief from chemotherapy-induced pain. BBSRC-funded researchers at King's College London made the discovery when researching ...

User comments : 0

More news stories

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Study says we're over the hill at 24

(Medical Xpress)—It's a hard pill to swallow, but if you're over 24 years of age you've already reached your peak in terms of your cognitive motor performance, according to a new Simon Fraser University study.

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.