AsianScientist (Jul. 26, 2016) – If you’ve ever scratched the life out of mosquito bites, chicken pox scars or a skin rash, you may have wondered how the itch happens in the first place. Now, researchers from China and the US may have uncovered a new pathway through which sensory nerve cells transmit that ever-annoying itching sensation.
Furthermore, the researchers discovered that two types of calcium ion channels in sensory nerve cells ‘tag team’ to send itch signals to the spinal cord, which neurons then direct to the brain. Their findings were published in Science Signaling.
“Itch is an important defense or warning mechanism for animals; maybe less so for humans now, due to better living conditions,” Professor Chen Zhou-Feng, the lead investigator on the study and director of the Washington University School of Medicine’s Center for the Study of Itch, told Asian Scientist Magazine.
“The itching sensation reminds animals of potential dangers to their skin and bodies that other sensations such as pain, touch, and temperature cannot. Chronic itch, however, is a major medical problem that so far is resistant to effective treatments.”
Our perception of the itch sensation is regulated by the transient receptor potential (TRP) family of calcium ion channels. These channels allow for the transport of calcium ions from one nerve cell to another, which is how these cells transmit itch signals.
The researchers focused on two types of itch signals: histamine-induced itching and chloroquine-induced itching. The former is caused by bug bites and is normally treated with antihistamines, while the latter is caused by the anti-malarial drug, chloroquine. These two types of itch were previously thought to be transmitted by different sets of ion channels.
During the study, it was puzzling to discover that mice that were genetically engineered without the channels that process histamine signals still scratched when exposed to histamine. The same reaction occurred when genetically engineered mice without the chloroquine channels were exposed to chloroquine.
By studying the dorsal root ganglion structure, a structure near the spinal cord which is full of sensory nerve cells, the researchers discovered a type of ion channel called TRPV4 that can transmit multiple types of itch, including histamine- and chloroquine-induced itch. They showed that a second type of ion channel, TRPV1, works in concert with TRPV4 to process these itch signals, acting as a kind of ‘molecular chaperone’ to TRPV4.
“Our finding suggests that by blocking one channel called TRPV4, we may be able to treat different types of itch conditions, including allergy-induced itch and chloroquine-induced itch,” Chen said.
Chen hopes that future research may lead to novel drugs that target TRPV4 to alleviate chronic itch.
The article can be found at: Kim et al. (2016) Facilitation of TRPV4 by TRPV1 is Required for Itch Transmission in Some Sensory Neuron Populations.
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Copyright: Asian Scientist Magazine; Photo: John Benson/Flickr/CC.
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