“Why are we scratching?“. This is the question asked by Julien Alexandre to the drafting of Sciences and the Future on our Facebook page. This is our question of the week, and here is our answer. Thank you all for your participation and your loyalty.
Complex molecular pathways
An answer to this question was put forward in 2016, in an article published in the journal Journal of Biological Chemistry. Researchers at Duke University in the United States explain that they have identified in mice the protein responsible for the urge to scratch. Called TRPV4, it is present in the upper layer of the dermis. To prove the involvement of this protein, the researchers exposed genetically engineered mice deprived of TRPV4 in skin cells to allergenic chemicals causing itching. Rodents hardly suffered from it, however.
According to the study, when the protein activates, it causes skin cells to release a molecule called “endothelin-1”, which is involved in the sensations of pain and itching. In addition, the researchers discovered that the activation of TRPV4 triggers a “flood” of calcium in the cell, which activates another protein called ERK, also involved in an itch, as mentioned. Sciences and the Future in a previous article. The researchers then wanted to develop drugs for the itch by blocking the molecular pathways involved. Moreover, already in 2016, they had succeeded in developing an ointment blocking TRPV4 and ERK in mice.
A video, posted to the TED online conference Youtube channel, more broadly referred to the itchiness of a mosquito bite. In this case, by biting, the mosquito releases an anticoagulant compound in the body of its victim. Problem: we are slightly allergic to it. It therefore leads to the release of a chemical compound called histamine, which will cause an enlargement of the diameter of the blood vessels, hence an acceleration of the immune response in the affected area. But histamine also triggers the activity of nerves related to the itch.
The vicious cycle of itching
You have surely noticed that when an area itches, and you scratch yourself, sometimes you want to scratch even more … until you hurt yourself. In 2014, this vicious cycle of itching was investigated by the University of Washington Center for the Study of Itching. According to him, when we scratch, we replace the itch with a very slight sensation of pain that causes the brain to release serotonin into the body. By replacing the itching, this sensation therefore appears pleasant, even though it is in fact a pain, even if it is minimal.
The problem is that by dint of scratching, this sensation will intensify and thus reveal its true nature: a painful burn. “As serotonin spreads from the brain to the spinal cord, we have found that the chemical can ‘derail’ and pass from pain-sensitive neurons to nerve cells which can influence the intensity of the itch., explained Zhou-Feng Chen, director of the Itch Study Center behind the study published in the journal Neuron and relayed by Sciences and the Future. Scratching can ease the itch by replacing it with mild pain. But when the body responds to pain signals, that response intensifies the itch even more.“So the ideal is to avoid scratching. Even when it does itch.