Cold feeling traced to source

December 18, 2007

For the first time, neuroscientists have visualized cold fibers – strands reaching from sensory neurons near the spinal cord to nerve endings in the skin tuned to sense different types of cold. The study and pictures appear in the Dec. 19 issue of the Journal of Neuroscience.

Surprisingly, given the highly diversified sensory system and the range of sensations studied – harmless cool, stinging cold, soothing coolness – the fibers lead back to one place in the neuron: a protein known as TRPM8 that relays a cold signal up the spinal cord to the brain.

The idea of a cold fiber is simple. When the dentist chills a tooth with compressed air, the fiber carries a signal from nerve ending to sensory neuron. The neuron relays the signal to the brain, and the patient shivers.

In practice, said USC study leader David McKemy, “no one’s actually seen a specific cold fiber.”

McKemy’s study solved that problem by genetically engineering mice in which neurons that express TRPM8 molecules also included a fluorescent tracer that lights up the fibers.

McKemy’s study provides the first visualization of cold-sensing, TRPM8-expressing neurons. Previous studies had shown that mice lacking TRPM8 lose much of their cold sensitivity (video available at www.nature.com/nature/journal/ … nfo/nature05910.html ).

Humans and other mammals appear to share the same mechanism, McKemy said.

By following the fluorescent cold fibers, the researchers added to the evidence that TRPM8 is involved in several types of cold sensing. In teeth, the distinct nerve endings involved in the initial shooting pain and the subsequent dull ache both lead back to TRPM8, McKemy said.

Sensations such as the pleasant coolness of menthol, the sting of ice on the skin, the heightened cold sensitivity after an injury and the soothing cool of some pain relief lotions also involve TRPM8, he added.

Removing TRPM8 does not eliminate all sensitivity to all types of cold. Extreme cold not only activates TRPM8 but also burns the skin, turning on many other warning circuits.

“Cold is going to be activating these cool and cold cells that likely are the ones we’re studying in this paper as well as activating these neurons that are probably responding to tissue damage,” McKemy said.

“So your higher cognitive centers are processing a cool signal and a pain signal, and so we get cold pain.

“As with anything with biology, it’s not as simple as you would think.”

McKemy was the lead author of a landmark 2002 study, published in Nature, that first identified the cold-sensing role of TRPM8.

One larger goal of such research is to understand the molecular mechanisms of sensation, in the hope of developing better drugs for relief of chronic pain states, such as arthritis and inflammation.

“If we understand the basic nuts and bolts of the molecules and neurons and how they detect pain normally,” McKemy said, “then perhaps we can figure out why we detect pain when we shouldn’t.”

Source: University of Southern California

Explore further: The sensation of cold is shut down by inflammation

Related Stories

The sensation of cold is shut down by inflammation

July 2, 2012
(Medical Xpress) -- Research groups at the University of Cambridge and the Instituto de Neurociencias, in Spain, have discovered a new and unexpected mechanism by which cold sensation is regulated, and opens up the possibility ...

Why menthol chills your mouth when it's not actually cold

January 22, 2015
Try putting an ice-cube in your mouth. The insides of your mouth and tongue instantly turn numb. Hold it in still and you will feel pain. Now try sucking on peppermint. The mint itself is at room temperature, but your mouth ...

Stopping cold: Scientists turn off the ability to feel cold

February 14, 2013
(Medical Xpress)—USC neuroscientists have isolated chills at a cellular level, identifying the sensory network of neurons in the skin that relays the sensation of cold.

Pain and itch connected down deep

May 2, 2011
A new study of itch adds to growing evidence that the chemical signals that make us want to scratch are the same signals that make us wince in pain.

Recommended for you

Hibernating ground squirrels provide clues to new stroke treatments

November 17, 2017
In the fight against brain damage caused by stroke, researchers have turned to an unlikely source of inspiration: hibernating ground squirrels.

Age and gut bacteria contribute to multiple sclerosis disease progression

November 17, 2017
Researchers at Rutgers Robert Wood Johnson Medical School published a study suggesting that gut bacteria at young age can contribute to multiple sclerosis (MS) disease onset and progression.

Molecular guardian defends cells, organs against excess cholesterol

November 16, 2017
A team of researchers at the Harvard T. H. Chan School of Public Health has illuminated a critical player in cholesterol metabolism that acts as a molecular guardian in cells to help maintain cholesterol levels within a safe, ...

Prototype ear plug sensor could improve monitoring of vital signs

November 16, 2017
Scientists have developed a sensor that fits in the ear, with the aim of monitoring the heart, brain and lungs functions for health and fitness.

Ancient enzyme could boost power of liquid biopsies to detect and profile cancers

November 16, 2017
Scientists are developing a set of medical tests called liquid biopsies that can rapidly detect the presence of cancers, infectious diseases and other conditions from only a small blood sample. Researchers at The University ...

FDA to crack down on risky stem cell offerings

November 16, 2017
U.S. health authorities announced plans Thursday to crack down on doctors pushing stem cell procedures that pose the gravest risks to patients amid an effort to police a burgeoning medical field that previously has received ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.