Why diving marine mammals resist brain damage from ...(emarkable capacity for increasing neurop...)

The study appears online December 18th in the Proceedings of The Royal Society B. Williams is lead author of the paper, entitled "Running, swimming and diving modifies neuroprotecting globins in the mammalian brain."

Scientists have long wondered why marine mammals are so tolerant of hypoxia. The conventional wisdom was that they had evolved physiological adaptations that increased the delivery of oxygen to the brain--for example, higher capillary density and blood flow that could be shunted preferentially to the brain. But despite such adaptations, blood oxygen levels still plummet after just a few minutes underwater, according to recent studies by Williams's group and others. How marine mammals could keep their vital organs alive on such low levels of oxygen remained a mystery.

Some unknown factor seemed to be involved, and Williams's attention recently turned to new types of globins that were discovered in 2000. Called neuroglobins and cytoglobins, these oxygen-carrying proteins reside in the brain tissue. That distinguishes them from hemoglobin, a similar iron-containing protein complex that carries oxygen in the blood and circulates throughout the body. Another molecular relative, myoglobin, facilitates oxygen delivery only in muscle tissue.

Scientists are still investigating the physical chemistry of these brain globins. So far, the evidence suggests that cytoglobins could play a role in efficiently moving oxygen out of the blood and into the brain, even when oxygen levels are extremely low, Williams said. The brain's neuroglobins, on the other hand, appear to be able to grab reactive oxygen and prevent the formation of destru
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