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Who Knew? A Neural Circuit Just for Itching

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Itch line (red) with touch, pain, and temperature lines (white) going through DRG before going to the spinal cord.

Itch-inducing agents activate a discrete population of peripheral sensory neurons that produce a signaling molecule called natriuretic polypeptide b (Nppb). The release of Nppb from these primary pruriceptive neurons triggers a dedicated itch biocircuit to generate the sensation of itch. [Images courtesy of Mark Hoon, National Institute of Dental and Craniofacial Research, NIH]

The occasional itch—be it a bug bite or rash—is annoying. But there are millions of people with chronic itching conditions, like eczema and psoriasis, who are constantly scratching their skin. This is more than a little irritation—it drastically reduces their quality of life and is a perpetual distraction. Current anti-itch treatments include topical corticosteroid creams, oral antihistamines, and various lotions. But researchers at NIH have gone beyond the skin’s surface and discovered a critical molecule at the root of that itchy feeling [1].

Mouse scratching it's earUntil now, it’s been unclear how the sensation of itching was carried to the brain. Was this a separate system, or did it use the same nerve pathways as pain, touch, or temperature? To find out, the researchers focused on a special group of nerve cells called “TRPV1 neurons,” which extend to the skin and detect temperature, various types of pain, and itch. These neurons use several chemicals to transmit signals; one of those is a neurotransmitter called Nppb. When the researchers created mice lacking Nppb, the mice became immune to itching. Even when the researchers exposed the mice to several itchy substances, such as histamine, the mice refused to scratch!

When the researchers actually removed specific spinal cord nerves that receive the Nppb itch signals, other sensations—like pain, touch, and temperature—remained intact. So we now know that in mice, and possibly in humans, there are specific nerve cells and brain circuitry that are entirely devoted to that itchy feeling. That means blocking Nppb could turn out to be a safe and effective strategy to cure itching, especially in chronic cases.

Reference: 

[1] The cells and circuitry for itch responses in mice. Mishra SK, Hoon MA. Science. 2013 May 24;340(6135):968-71.

NIH support: National Institute of Dental and Craniofacial Research

31 Comments

  • Mawakana Motilewa says:

    A gargantuan “THANK YOU!” for publishing an article that provides potential relief – and certainly a measure of clarity – for the millions suffering the affliction of chronic itching.

    I intend to help spread this article, for I have friends and acquaintances who have friends and acquaintances wanting understanding – and a solution.

  • waynebergloff says:

    I have had an itch on my arms & legs now for approximately a year. My dermatologist has given me different lotions, but they haven’t stopped the itch … perhaps this is what will help.
    Thank you,
    Wayne

    • Michael C. says:

      I have kidney disease and the intense itching was horrible. Then I tried a pepper itch spray … it works incredibly well. It’s the only thing that worked for me and lots of other kidney patients use it too. It supposedly blocks the itch pathway.

  • Dr.Nita Kedar says:

    Congrats sir! I think this research work will truly help the patients with psoriasis.

  • James Fant says:

    Thanks so much for posting this article. Hopefully this research will also help sufferers of dermatographism.

  • Anjali Shukla says:

    This is very fascinating and surely presents a very encouraging possibility for curing itch associated with psoriasis and other diseases! Congratulations to Drs Mishra and Hoon for the discovery. NIH scientists rock!

  • D.I. says:

    Itch has been a very bad thing that ever happens in the body. So, this is gonna help those who got fed up with their itching.

  • ghaf says:

    amazing

  • Plato microondas says:

    Great post, very interesting article

  • B.P. says:

    I really have fun while reading these posts. I just love them … very excellent!

  • Erni Fields says:

    This is such wonderful news for those of us who are the sufferers of chronic itching. Thank You. Does this also works for dogs? Our little Yorkie suffers from this, and it has been absolutely maddening that so far none of the suggestions, including medical, have provided any long term relief.

  • marlene klotz says:

    This article is so wonderful because it represents hope for anyone who suffers from the dreadful effects of itching, both physical and psychological. These posts are a true
    learning experience. . . .

  • Mary Olson says:

    I have suffered from extreme head itching and arms and legs ever since I had a left lung transplant on Feb.20, 2007. It would be so amazing to find out why and how to allevate this
    irritation!!!!

  • Cynthia Ely says:

    So glad that this important research is being conducted.
    Finally, some light at the end of the tunnel! Will follow this essential research.

  • Paul Hummer says:

    OMG…….. there might be hope for eczema and psoriasis.

    Thanks!!!

  • Meivy dos Santos says:

    My 8yr old daughter has suffered from eczema since she was 6 months. We’ve tried everything, but she’s still itchy. I have always wished for a magical button to make it all go away. I’m so glad you found it!

  • Gina LaGrange says:

    Great news! How do you block Nppb? When will doctors be ready to do the procedure? We are ready yesterday.

    • Mark Hoon says:

      Gina,

      Thanks for your interest in our research. While our discovery provides important new knowledge, it also represents the beginning of a longer research process to find other unique molecules related to our discovery that can be better targeted to control chronic itch. It is often said that one can’t put a timeframe on science. That’s truly the case here. The research must proceed at its own pace to find these molecules and ensure their safety and effectiveness for people. But what’s nice is our discovery helps to put us on the right track to find those needed better treatments. I wish that I could help you with alleviating your chronic itch condition.

      Thanks again for your interest in our research and the National Institutes of Health.

      Mark Hoon

  • Florian M. Hocke says:

    I have had eczema since I was 6 months old, I am now a 71 year young male. I also have osteoarthritis (OA) and use a doctor’s prescribed topical gel for the OA pain. The topical is … diclofenac sodium 1%. I noticed that when I applied it to my OA pain sites that the eczema on my hands also stopped itching. I now apply it to my eczema flair ups (all though it stings a little for a minute)and now I am comfortable. I still use moisturizers and cortisone topicals.

  • Patti Barrett says:

    I have had severe eczema from head to toe since the day I was born and have been told my entire life that I will “outgrow” my eczema. Well, 60 years later….I am still waiting. Please find this nerve in my system and eliminate it! People with “normal” skin have no idea how much eczema itches and the constant emotional torment it causes. We don’t enjoy scratching….it’s a necessity….one I wish I didn’t need.
    DOWN WITH Nppb!

  • jean says:

    My daughter has atopic dermatitis (AD) since she was a month old, usually controlled by steroid creams. But since she turned 14, she is now classified with severe AD and severe puritis 24/7 where nothing helps. It would be amazing if this helped her have some normalcy to life. Any idea when this will be put to the test on humans? Any studies being done with volunteers?
    Thank you,
    Jean

    • Mark Hoon says:

      Jean,

      There has been a great deal of interest in our work from the public and researching in the field. It is clear there is a huge need for better treatments, but unfortunately results from the lab take time to be tested to ensure safety and that they work in humans. I wish that I could help you with alleviating your daughter’s chronic itch condition. However, at this point in time, we don’t have any studies under way for people, neither do we foresee starting any in the near future.

      Thanks again for your interest in our research and the National Institutes of Health.

  • Amy Hoffman says:

    Seems so simple -block the signal that gives the itch feeling. Hope this takes months not years. I have also had ezcema since a baby and spent the last 50 years on steroids so much that my skin has thinned horribly. Finally found relief with narrowband UVB therapy. Side effects but worth it not to wake up to bloody sheets and clothes from scratching.

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