Ever wonder what causes you to itch? A research team from the National Institutes of Health has discovered a molecule on the spinal cords of mice that triggers an itching sensation in the brain. Scientists believe a similar process is duplicable in humans, considering the similarities of our nervous system to that of a mouse.
"Our work shows that itch, once thought to be a low-level form of pain, is a distinct sensation that is uniquely hardwired into the nervous system with the biochemical equivalent of its own dedicated land line to the brain," said the study's lead author Mark Hoon, Ph.D.
Itching, or pruritus, could stem from something as simple as dried skin or could be a sign of a more serious condition like eczema or psoriasis. These incurable chronic skin conditions are characterized by skin inflammation or a thick layer of red plaque.
Hoon and fellow researcher Santosh Mishra examined groups of nerve cell endings along each mouse's spinal cord. These neurotransmitters are responsible for monitoring external bodily conditions including pain, body temperature, and itching.
When all the molecules were identified, the scientists began screening each one to analyze the effect it had on the animal test subjects. One molecule, responsible for connecting nerve cells in the spinal cord to the central nervous system, displayed a desired effect in itchy mice. When the tiny molecule natriuretic polypeptide b (Nppb) or its connected nerve cell got extracted from the mouse's spinal cord, itching seemed to stop.
"We tested Nppb for its possible role in various sensations without success," said Mishra.
"When we exposed the Nppb-deficient mice to several itch-inducing substances, it was amazing to watch. Nothing happened. The mice wouldn't scratch."
Although significant to dermatology research, Hoon and Mishra know it will be a while until their findings can be translated into an approved treatment for chronic skin condition. Removal of Nppb isn't as simple as it seems due to its connection to other major organs including the heart and kidneys.
"The larger scientific point remains. We have defined in the mouse the primary itch-initiating neurons and figured out the first three steps in the pruritic pathway," Hoon concluded.
"Now the challenge is to find similar biocircuitry in people, evaluate what's there, and identify unique molecules that can be targeted to turn off chronic itch without causing unwanted side effects. So, this is a start, not a finish."
The results of this study were published in the May 24 online edition of Science.
Source: Mishra S, Hoon M. The Cells and Circuitry for Itch Responses in Mice. Science. 2013