From: Reuters
Published December 19, 2007 08:57 AM

Brrrr: Scientists trace the roots of feeling cold

By Julie Steenhuysen

CHICAGO (Reuters) - Nerves that sense the icy slap of an arctic wind or just a cool breeze take their orders from a single protein, U.S. researchers said on Monday, shedding new light on how we experience cold.

Prior studies have suggested cold-sensing neurons are specialized, with some detecting painful cold sensations and others detecting more pleasant ones.

But researchers at the University of Southern California have found that even though most cold-sensing neurons make use of a single protein known as TRPM8, they can detect a range of sensations.

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"We all know when we stimulate our teeth with cold we get this distinct cold sensation," said David McKemy, whose study appears in the Journal of Neuroscience.

"You get this sharp transient shooting pain and this dulled, aching sensation," McKemy said in a telephone interview.

Other groups have attributed that to two different cold sensory neurons. "There was a notion that there were neurons called cool fibers and there were others involved in detecting cold pain," he said.

He said he had expected neurons that express, or produce, TRPM8 to be of the pleasant cool variety.

To study the neurons, McKemy genetically engineered mice so that neuron fibers that expressed this protein would be fluorescent green. He then traced these cold-sensing fibers from sensory neurons near the spinal cord to nerve endings in the skin.

"What our study suggests is that even though these neurons express this single protein, it looks like they have diverse functions," he said.

Humans appear to share the same mechanism, he said.

McKemy said nerves that produce TRPM8 account for about 75 percent of all cold-sensing neurons. He believes there are others that are specific to pain, such as when the skin is burned in frostbite.

Researchers study cold-sensing neurons to grasp the molecular mechanisms of sensation, an understanding that may lead to better drugs for pain relief.

"If we understand the basic nuts and bolts of the molecules and neurons and how they detect pain normally, then perhaps we can figure out why we detect pain when we shouldn't," McKemy said in a statement.

(Editing by Maggie Fox and Todd Eastham)

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