Navigation Links
Itchy wool sweaters explained

Johns Hopkins researchers have uncovered strong evidence that mice have a specific set of nerve cells that signal itch but not pain, a finding that may settle a decades-long debate about these sensations, and, if confirmed in humans, help in developing treatments for chronic itch, including itch caused by life-saving medications.

At the heart of their discovery is a type of sensory nerve cell whose endings receive information from the skin and relay it to other nerves in the spinal cord, which then coordinates a response to the stimulus. Published online Dec. 23 in Nature Neuroscience, a report on the research suggests that even when the itch-specific nerve cells receive stimuli that are normally pain-inducing, the message they send isn't "That hurts!" but rather "That itches!"

Pain and itch are both important sensations that help organisms survive. And pain is arguably more important because it tells us to withdraw the pained body part in order to prevent tissue damage. But itch also warns us of the presence of irritants, as in an allergic reaction. However, "when either of these sensations continues for weeks or months, they are no longer helpful. We even see patients stop taking life-saving medications because they cause such horrible itchiness all over," says Xinzhong Dong, a Howard Hughes early career scientist and associate professor of neuroscience at the Institute of Basic Biomedical Sciences at the Johns Hopkins University School of Medicine. "And sometimes when we try to suppress chronic pain, with morphine for example, we end up causing chronic itchiness. So the two sensations are somehow related, and this study has begun to untangle them," he says.

Because nerve cells send their messages as electrical currents that flow through them just as they would through wires, scientists can plug tiny monitors into individual nerve cells to detect the moment of stimulation. The scientific controversy over pain and itch centers around a group of nerve cells known to respond electrically to painful stimuli such as molecules of capsaicin, the fiery ingredient in chili peppers. A small subset of these nerve cells also responds electrically to itchy stimuli because they have on their surfaces receptors for molecules like histamine. One of these itchy receptors, called MrgA3, binds the anti-malaria drug chloroquine, causing serious itchiness in many patients.

Sensory nerve scientists have not known whether the nerves with itchy receptors and pain receptors were actually sending both types of messages to the brain, or just itch messages. What the current study found is that, in nerves with the itchy receptor MrgA3, electrical signals sent in response to both painful and itchy stimuli are interpreted by the brain as itch.

To reach this conclusion, the researchers first used a genetic trick to label the MrgA3 cells in mice with a glowing protein that allowed them to see the cells under the microscope. Aided by the glow, they were able to plug in those tiny electricity monitors and watch nerve cell responses to different stimuli. The cells transmitted electrical signals when the mice were exposed to itch-inducing chloroquine and histamine, as well as pain-inducing capsaicin and heat. Based on this result, the researchers tentatively concluded that the cells could send both pain and itch signals.

In the next experiment, the researchers monitored the behavioral responses of mice to the different stimuli. As expected, when the tails of normal mice were placed in hot water, they quickly pulled them out; when normal mice were given a bit of chloroquine or histamine, they scratched vigorously with their hind legs.

Then, to examine the role of MrgA3 cells in pain and itch, the scientists selectively killed MrgA3 nerve cells in adult mice and retested their responses. Presumably, the researchers noted, because MrgA3 cells are only a small fraction of all pain-sensing nerve cells, the mice had normal withdrawal responses to painful stimuli like hot water. However, when exposed to itchy stimuli, their scratching responses were reduced to varying degrees depending on the stimulus, most significantly in response to chloroquine. The fact that some stimuli still caused scratching suggested to the scientists that MrgA3 cells are not the only ones in the body that respond to itch. "We were convinced that MrgA3 cells are responsible for much of the sensation of itch, but it wasn't yet clear whether MrgA3 cells could also relay painful information," says Dong.

In their final experiments, the scientists used genetic techniques to create mice in which the MrgA3 cells were the only cells in the body capable of responding to capsaicin, that peppery pain-inducing substance. When injected into the cheeks of mice, normal mice massage the area with their forepaws to relieve the hot sensation. When injected into the experimental mice, they vigorously scratched their cheeks with their hind legs, suggesting that this normally painful stimulus had been communicated to the brain by MrgA3 cells as itchiness.

"Now that we have disentangled these itchy sensations from painful ones, we should be able to design drugs that target itch-specific nerve cells to combat chronic itchiness," says Dong. "We hope that this will not only provide relief, but also increase people's faithfulness to their drug plans, particularly for deadly diseases like malaria and cancer."


Contact: Catherine Kolf
Johns Hopkins Medicine

Related medicine news :

1. Fast-acting enzymes with 2 fingers: Protein structurally and dynamically explained
2. Psychologist Steve Wilson: Post-Holiday Let-Down May be Worse Than the Holiday Blues as Explained in New Handbook
3. Queens research gives fresh hope to couples with unexplained infertility
4. Rise in Pregnancy-Associated Cancers Not Fully Explained by Older Age
5. US Drug Watchdog Now Offers to Help All Woman Who Used Fosamax For Osteoporosis and Then Had an Unexplained a Femur Break Get to the Best Attorneys
6. Wake Forest Baptist research provides clue to unexplained excited delirium deaths
7. The REMARK checklist explained: How to use guidelines on reporting tumor marker prognostic studies
Post Your Comments:
Related Image:
Itchy wool sweaters explained
(Date:11/30/2015)... ... November 30, 2015 , ... The successful filing of an Investigational New Drug ... so important to this key industry segment, Regis Technologies has decided to sponsor and ... 4th at 11am EST. , Federal law does not allow new drugs to cross ...
(Date:11/30/2015)... ... November 30, 2015 , ... SIMmersion’s ... importance to the medical schools of the future. To reach an audience of ... the 2015 ChangeMedEd conference in Chicago, organized by the American Medical Association. ...
(Date:11/30/2015)... ... November 30, 2015 , ... ... announce their strategic partnership at the Radiological Society of North America (RSNA) ... Winscribe, global providers of cutting-edge dictation and speech-enabled documentation software, announced their ...
(Date:11/30/2015)... ... November 30, 2015 , ... Bayco Products, Inc today announced the introduction of three Nightstick® brand ... choice of three different colors; red ( NSP-1632 ), yellow ( NSP-1634 ) and blue ... hours in constant-on mode, or 27 hours in blinking strobe mode using a fresh set ...
(Date:11/29/2015)... ... November 30, 2015 , ... The Cyber Monday deal is a deep 40% or more discount ... to get gifts for the skin care lover in your circle. Each Christmas, Sublime ... This year, the 3 serums are staples: Collagen, Retinol and Hyaluronic Serums. , Stocking stuffers ...
Breaking Medicine News(10 mins):
(Date:11/26/2015)... , Nov. 26, 2015 Research ... addition of the "2016 Future Horizons and ... (TDM) Market: Supplier Shares, Country Segment Forecasts, Competitive ... --> --> ... analysis of the Japanese therapeutic drug monitoring market, ...
(Date:11/26/2015)... 2015 ) ... "2016 Future Horizons and Growth Strategies in ... Supplier Shares, Country Segment Forecasts, Competitive Intelligence, ... --> ) has announced ... Horizons and Growth Strategies in the German ...
(Date:11/26/2015)... DUBLIN , November 26, 2015 ... has announced the addition of the  ... in the European Therapeutic Drug Monitoring ... Forecasts, Competitive Intelligence, Emerging Opportunities"  report ... ) has announced the addition ...
Breaking Medicine Technology: