Dr. Zhou-Feng Chen is an associate professor at the Washington University School of Medicine, where he studies the molecular and cellular mechanisms of pain and itch sensations and the role of the central serotonergic system in animal behavior. Along with his colleagues, he authored a paper on the discovery of itch-specific neurons, which appeared in the journal Science Express on August 6 online issue.
Scientists find itchiness neurons
Chinese scientists have pinpointed the group of neurons in mice that respond to itchy stimuli and tell the brain it's time to start scratching. These findings may themselves scratch a longstanding itch in neuroscience: the question of whether the nervous system handles the sensations of pain and itchiness the same way. Researchers have debated whether itch is basically just a type of pain or whether separate neural pathways are devoted to itchiness, pain and other sensations (the "labeled line hypothesis"). Thus far, the evidence for this hypothesis has been inconsistent, but a new study by Yan-Gang Sun should help put this debate to rest. The researchers had previously determined that a neuronal receptor called the GRPR receptor is involved in sensing itchy stimuli but not pain. Now, they show that mice whose spinal cords lacked neurons with GRPR receptors do not scratch in response to itchy stimuli, though their ability to feel pain is the same as that of normal mice. The GRPR-expressing neurons turn out to be distinct from another group of neurons, the spinothalamic tract neurons, that had previously been the focus of the debate. The new findings thus suggest that GRPR-expressing neurons constitute a long-sought "labeled line" for itch sensation in the spinal cord.
What are the chief findings of your research?
We have found the first itch receptor and itch-specific neurons in the spinal cord. We have provided molecular and cellular evidence supporting the idea that itch and pain are two distinct sensations. Our studies should help to settle an important issue that has been debated for nearly a century.
How does this challenge what was previously known?
For nearly a century, many scientists have considered the itch sensation as a weaker or minor form of pain. Although many believe that itch is a sensation independent of pain, compelling evidence for the existence of itch-specific neurons has been lacking. Prior to our studies, the mainstream view was that there are no itch-specific neurons in the spinal cord.
What applications does this have, and what are some potential uses of your research?
Our studies have important clinical implications; Primarily, we have provided potential molecular and cellular bases for treating chronic itch. If itch-specific neurons exist in humans, we may be able to relieve chronic itch by blocking the function of itch genes or itch neurons. Just like mice without itch sensation, we may feel itch sensation no more, which will be very good news for many people who suffer from chronic itch. Importantly, such itch-specific treatment will not interfere with our other sensations.
How was it that the mice in your experiment did not experience an itching sensation?
Mice without itch neurons in the spinal cord were not bothered by injection of itching substances, no matter how strong they were. In contrast, mice with normal itch neurons scratched vigorously after injection of itching substances.
What is the next step for your research?
We are interested in two issues. First, besides GRPR, these itch neurons may contain other itch-specific genes. If we can find them, it will be very significant for the therapeutic design of anti-itch drugs. On the other hand, we would like to know more about these itch-specific cells. Such studies will greatly help us to understand why itch and pain are two different sensations.
These are Dr. Zhou-Feng Chen's written remarks. Please refer to the video interview for exact quotes.
Related Research Papers
Cellular Basis of Itch Sensation