No need to scratch (Image: Rengim Mutevellioglu/Getty)
THE intimate link between itch and pain has been teased apart for the first time – a development that could lead to powerful anaesthetics without any of that intolerable itching.
Itch is one of the most common side effects of the anaesthetics used in procedures such as epidurals. One explanation is that itch and pain receptors are intrinsically connected. “Itch and pain are two sensations that antagonise each other,” says from Washington University in St Louis, Missouri. “By scratching you create a kind of mechanical pain and suppress the itch. Conversely, if you suppress pain you see more itching.”
To understand this mechanism better, Chen used mice to study the action of morphine, a painkiller that can cause itching. Morphine works through a receptor called MOR, and Chen suspected that different variants of the receptor might be responsible for the itch and pain responses. His team bred mice lacking one form of this receptor, called MOR1D. These mice did not scratch themselves when given morphine, though they still felt its painkilling effect (Cell, ).
Advertisement
“It’s quite exciting that we are able to segregate the two,” says Cheng, who believes that separate pathways for pain and itch exist in humans too. “Our study suggests there are different ways that you can inhibit itch without interfering with analgesia.”
Another puzzle is that some itches do not respond to anti-itch drugs called antihistamines, and a study published this week suggests why. Antihistamines have proved effective against the itch of mosquito bites, for example, but they do little to soothe the itching caused by kidney failure, liver disease or burns, says at Johns Hopkins University in Baltimore, Maryland.
Antihistamine-sensitive itches have been shown to activate nerve fibres called unmyelinated C-fibres. Ringkamp suspected that itches that do not respond to the drugs might be mediated by a different type of fibre called myelinated A-fibres.
The spines of a tropical plant called cowage can irritate the skin and produce an itch that does not respond to antihistamines. To find out if the cowage itch signal passes through the myelinated A-fibres, Ringkamp and his team placed a weighted band over volunteers’ wrists to cut off conduction in the small A-fibres. When the team inserted cowage spines into the volunteers’ fingertips, they found that itch was dramatically reduced in many – but not all – of them (Journal of Neuroscience, ).
“It is fascinating that this happens in some people and not others,” says Glenn Geisler at the University of Minnesota in Minneapolis. “In future, drugs to treat itch would have to treat A and C fibres.”
![Astronomers have long known that understanding how star clusters come to be is key to unlocking other secrets of galactic evolution. Stars form in clusters, created when clouds of gas collapse under gravity. As more and more stars are born in a collapsing cloud, strong stellar winds, harsh ultraviolet radiation and the supernova explosions of massive stars eventually disperse the cloud, and their light can bear down on other star-forming regions in the galaxy. This process is called stellar feedback, and it means that most of the gas in a galaxy never gets used for star formation. Researching how star clusters develop can answer questions about star formation at a galactic scale. Now, the state of the art has been further developed with both Hubble and Webb working together to provide a broad-spectrum view of thousands of young star clusters. An international team of astronomers has pored over images of four nearby galaxies from the FEAST observing programme (#1783), trying to solve this mystery. Their results show that it is the most massive star clusters that clear away their gaseous shroud the fastest, and begin lighting their galaxy the earliest. The team identified nearly 9000 star clusters in the four galaxies in different evolutionary stages: young clusters just starting to emerge from their natal clouds of gas, clusters that had partially dispersed the gas (both from Webb images), and fully unobstructed clusters visible in optical light (found in Hubble images). With Webb???s ability to peer inside the gas clouds, they were able to then estimate the mass and age of each cluster from its light spectrum. This image shows a section of one of the spiral arms of Messier 51 (M51), one of the four galaxies studied in this work, as seen by Webb???s Near-Infrared Camera (NIRCam). The thick clumps of star-forming gas are shown here in red and orange, representing infrared light emitted by ionised gas, dust grains, and complex molecules such as polycyclic aromatic hydrocarbons (PAHs). Within these gas complexes, each tens or hundreds of light years across, Webb reveals the dense, extremely bright clusters of massive stars that have just recently formed. The countless stars strewn across the arm of the galaxy, many of which would be invisible to our eyes behind layers of dust, are also laid bare in infrared light. [Image description: A large, long portion of one of the spiral arms in galaxy M51. Red-orange, clumpy filaments of gas and dust that stretch in a chain from left to right comprise the arm. Shining cyan bubbles light up parts of the gas clouds from within, and gaps expose bright star clusters in these bubbles as glowing white dots. The whole image is dotted with small stars. A faint blue glow around the arm colours the otherwise dark background.]](https://images.newscientist.com/wp-content/uploads/2026/05/13114322/SEI_296271016.jpg)
