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Unbearable itch may no longer be a pain in anaesthesia
THIS WEEK
Kill pain without the unbearable itch 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 Zhou-Feng Chen 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
Clean thinking solves climate model problem GOOD news for climate modellers. After 25 years of trying, they have succeeded in simulating the hot climates of Earth’s prehistory. So why has it taken so long? Not because of the models themselves, but because the modellers made a false assumption: that aerosol pollution in the past was as bad as it is today. At various times in Earth’s history, the planet was much hotter than it is 16 | NewScientist | 22 October 2011
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, DOI: 10.1016/j.cell.2011.08.043).
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 Matthias Ringkamp 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, DOI: 10.1523/jneurosci.3005-11/2011). “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 –No need to scratch– A and C fibres.” n Image Source / Rex Features
Catherine de Lange
“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
now. Rocks and fossils laid down in these hothouse stretches show that the temperature difference between the poles and the equator was much smaller than it is today. Climate models have long failed to simulate these warm times – they don’t heat the poles enough, often falling as much as 15 °C short. Trying to fix this cold-pole problem, Jeff Kiehl of the National Center for Atmospheric Research in Boulder, Colorado, simulated an exceptionally hot climate that existed 55 million years ago – the PalaeoceneEocene thermal maximum. The average global temperature then was
35 °C – the average today is just 15 °C. Kiehl wondered whether the coldpole problem came from the assumptions used to run the models. Most of these are derived from studying the modern atmosphere, which is polluted with aerosols such as airborne soot. Water droplets condense around aerosols, so their presence affects the way clouds form and behave – with consequences for the climate.
“When he ran his model of the ancient climate with clean skies, the problem largely disappeared”
Assuming that 55 million years ago the atmosphere was a lot cleaner, Kiehl went back to a 2001 study which found that polluted areas have up to 400 water droplets per cubic centimetre of air, while less polluted ones have as few as 50. When he ran his model of the ancient climate with clean skies, the cold-pole problem largely disappeared. “It’s reassuring,” Kiehl says. “If this is the explanation, there isn’t anything drastically wrong with our climate models.” He presented his work last week in London at a Royal Society meeting on warm climates of the past. Michael Marshall n
Kill pain without the unbearable itch 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 Zhou-Feng Chen 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
Clean thinking solves climate model problem GOOD news for climate modellers. After 25 years of trying, they have succeeded in simulating the hot climates of Earth’s prehistory. So why has it taken so long? Not because of the models themselves, but because the modellers made a false assumption: that aerosol pollution in the past was as bad as it is today. At various times in Earth’s history, the planet was much hotter than it is 16 | NewScientist | 22 October 2011
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, DOI: 10.1016/j.cell.2011.08.043).
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 Matthias Ringkamp 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, DOI: 10.1523/jneurosci.3005-11/2011). “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 –No need to scratch– A and C fibres.” n Image Source / Rex Features
Catherine de Lange
“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
now. Rocks and fossils laid down in these hothouse stretches show that the temperature difference between the poles and the equator was much smaller than it is today. Climate models have long failed to simulate these warm times – they don’t heat the poles enough, often falling as much as 15 °C short. Trying to fix this cold-pole problem, Jeff Kiehl of the National Center for Atmospheric Research in Boulder, Colorado, simulated an exceptionally hot climate that existed 55 million years ago – the PalaeoceneEocene thermal maximum. The average global temperature then was
35 °C – the average today is just 15 °C. Kiehl wondered whether the coldpole problem came from the assumptions used to run the models. Most of these are derived from studying the modern atmosphere, which is polluted with aerosols such as airborne soot. Water droplets condense around aerosols, so their presence affects the way clouds form and behave – with consequences for the climate.
“When he ran his model of the ancient climate with clean skies, the problem largely disappeared”
Assuming that 55 million years ago the atmosphere was a lot cleaner, Kiehl went back to a 2001 study which found that polluted areas have up to 400 water droplets per cubic centimetre of air, while less polluted ones have as few as 50. When he ran his model of the ancient climate with clean skies, the cold-pole problem largely disappeared. “It’s reassuring,” Kiehl says. “If this is the explanation, there isn’t anything drastically wrong with our climate models.” He presented his work last week in London at a Royal Society meeting on warm climates of the past. Michael Marshall n