SCIENCE

"One of the really neat things about the new glider is the feet," said geologist Nicholas Fraser, director of research and collections at the museum, who found the fossils. "They are preserved in a hooked posture, which is unusual and strongly suggests a grasping habit, further emphasizing a lifestyle in the trees."

-- Christopher Lee

Some Nerves Resistant to Cold

Extreme cold is extremely dangerous.

Cold's hazards begin at an organism's surface -- usually its skin -- which can freeze and cease to be pliable or watertight. Penetrating deeper, cold can alter the function of muscles and tendons, essential for locomotion. The body's core, where the most complicated physiology occurs, is also temperature-sensitive. Below a certain temperature, the brain, the heart and other vital organs begin to work erratically and eventually stop.

So how does the body perceive life-threatening cold in time?

The simple answer is that it senses extreme cold as pain that it will go to great lengths to alleviate by . . . getting out of the cold. But that is harder to achieve than one might think. Cold affects the chemical and electrical function of nerves, causing them to fire sluggishly, and eventually go silent. A message like "Danger! Danger! Extreme Cold!" would seem to be always on the verge of being blocked by the effects of cold itself.

Katharina Zimmerman, Andreas Leffler, Peter W. Reeh and their colleagues at Friedrich-Alexander University in Germany explain in the current issue of Nature how the message gets through.

All nerves cells have "voltage-gated channels" in their membranes that let sodium ions flow in and out quickly, a key event in nerve firing. Using rats and mice, the researchers showed that some pain-signaling nerves have a specific channel subtype called Nav1.8, which works even at very low temperatures. It makes the nerves almost completely cold-resistant.

That channel is used for other purposes by coldblooded animals. Warmblooded animals employ it for a more specific purpose -- "to detect and avoid tissue-damaging levels of cold," the authors write.

The new findings help explain why cold hands and feet can be extremely painful long after they have lost fine sensation or why they can even be felt at all.

-- David Brown