Heres why we feel cold

December 19th, 2007 - 2:20 pm ICT by admin  

Washington, Dec 19 (ANI): Scientists have traced the roots of feeling cold by identifying a protein that plays a key role in sensing cold.

For the first time, neuroscientists at the University of Southern California 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.

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

But now, researchers have found that the fibres 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.

Lead author David McKemy explained the idea of a cold fibres as simple. When the dentist chills a tooth with compressed air, the fibres carries a signal from nerve ending to sensory neuron. The neuron relays the signal to the brain, and the patient shivers, he said.

“We all know when we stimulate our teeth with cold we get this distinct cold sensation,” said McKemy.

McKemys team genetically engineered mice in which neurons that express TRPM8 molecules also included a fluorescent tracer that lights up the fibres.

The study provides the first visualization of cold-sensing, TRPM8-expressing neurons.

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

By following the fluorescent cold fibres, 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, he 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 were 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, its not as simple as you would think, he added.

The study appears in the Dec. 19 issue of the Journal of Neuroscience. (ANI)

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