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Coming up for air - Can diving rats can show us how to treat brain damage?

点击量:   时间:2017-05-13 08:01:10

By Nell Boyce RATS divert blood to certain key parts of their brains as they swim underwater, researchers in Canada say. If people react in the same way, this discovery may help in the search for ways to treat strokes and other brain damage. Underwater responses have been well studied in marine mammals like seals. When their bodies are starved of oxygen, the flow of blood flow to their brains increases. Glenn Ollenberger and Nigel West at Saskatchewan University wanted to look at the diving response in a land-dwelling mammal. They chose rats because their neural anatomy is well known, making comparisons with humans easier. They hoped to find out whether the extra blood flow favoured some brain regions over others. While the rats swam round a small water-filled maze for roughly ten seconds, the researchers injected a radioactive tracer through catheters in the animals’ arteries and veins. They then used the amount of radioactivity in different parts of the rats’ brains to measure how much blood had flowed there. “This is the first experiment with free animals that are moving and thinking,” says Ollenberger. Most brain regions exhibited almost a twofold rise in blood flow, but a few regions such as the basal ganglia and the hippocampus and amygdala had no significant increases (Journal of Experimental Biology, vol 201, p 549). The researchers speculate that the body has this response because these areas are less prone to damage from oxygen starvation. “They were very clever about how they did this,” says Robert Bryan of Baylor College of Medicine in Houston, Texas, who researches cerebral circulation control. “You can’t just look at the flow to the brain—they also looked at small brain regions with high resolution.” Ollenberger and West suspect that the diving response is triggered by an increase in levels of carbon dioxide, which dilates blood vessels. When they repeated the experiment while the rats breathed a mixture containing a normal concentration of carbon dioxide but less oxygen, they saw no increase in cerebral blood flow. Ollenberger believes a similar response occurs in humans, and has started to look at it directly. He injects volunteers with a radioisotope before they dunk their heads in a bucket of water, while a camera sensitive to gamma rays measures the blood flow in the brain. “This may reveal regions of the brain susceptible to damage during drowning,” says Ollenberger. He hopes that by understanding more about how the body conserves oxygen and the mixture of gases that sparks the response,