16 | NewScientist | 8 November 2014

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Itch, scratch, itch scratch, ouch!

IT’S the sweetest relief… until it’s not. Scratching an itch only gives temporary respite before making it worse. We now know why.

We know the neurotransmitter serotonin helps control pain, and that pain helps relieve an itch, so a team led by Zhou-Feng Chen at the Washington University School of Medicine in St Louis, Missouri, wondered whether serotonin is also involved in the itch itself.

They found that it was – mice genetically modified to produce no serotonin had almost no urge to scratch when injected with an itchy chemical. Conversely, normal mice scratched more after they were injected with extra serotonin.

But that’s not the end of it. A few years ago, Chen’s team discovered that activating brain cells called GRPR neurons makes the itch sensation stronger. They’ve now shown that GM mice lacking this type of brain cell show no urge to scratch after a dose of serotonin. This suggests that on its way to the itch site, the neurotransmitter gets its wires crossed and activates the itch-amplifying GRPR neurons as well as pain-controlling neurons.

So when we scratch an itch, the extra serotonin the brain releases to control the pain not only makes us scratch more to get continued relief, but also aggravates the itch itself, says Chen (Neuron, doi.org/ws8).

Centaurs galloped into Saturn’s rings

SATURN’S rings were the victim of a hit-and-run – and the culprits may be centaurs, strange objects that are part icy comet, part rocky asteroid.

In earlier work with images from the Cassini spacecraft, Matthew Hedman, now at the University of Idaho, noticed that two of the planet’s rings sported alternating bright and dark bands. He argued they were low hills and valleys caused by a small comet that had smacked into the rings. The features could be seen getting smaller over time, suggesting the impact occurred in 1983.

Now, he and colleagues have found that the collision shoved the ring particles side to side as well as up and down. That let them work out the angle of the incoming object – nearly perpendicular to the ring plane.

Using data from the Minor Planet Center, they found two objects with the right orbit to be the perpetrators of the collision. Both were centaurs, travelling on unstable orbits in the outer solar system (Icarus, in press).

The rings may not settle down any time soon, Hedman adds. There is evidence that similar patterns in other rings are hundreds of years old.

CHEMICALS originally used to clean pipes and now prescribed as a drug for osteoporosis could also be bad news for breast cancer.

Bisphosphonates are chemicals with a remarkable ability to bind to calcium – whether that’s in calcified pipes or in bones, where they help increase bone density.

Tiny granules of calcium are also found in breast tumours and there is some evidence that taking bisphosphates extends the lives of women with breast cancer.

To explore further, Mike Rogers from the Garvan Institute in

Sydney, Australia, and colleagues tagged bisphosphonate molecules with a chemical that glows under a microscope. They gave the drugs to mice bred to develop breast cancer and used the glow to watch their activity. The bisphosphonates leaked from the veins running through the tumour and bound to the breast calcifications. Then they were gobbled up by a type of white blood cell.

Next, the team gave the glowing version of the drug to a woman with breast cancer. Analysing the primary tumour after it had been

surgically removed, they saw that it had been infiltrated by white blood cells (Cancer Discovery, in press). This is important, as one of the reasons tumour cells are so pernicious is that they are able to hide from the body’s immune system. The fact that the white blood cells were able to get into the tumour suggests that the bisphosphonate is somehow alerting the body to its presence.

The next step is to see how the drug affects breast cancer progression and work out exactly how it influences white blood cells.

Bone drug hunts down calcium in breast tumours

Slither of DNA finds snakebite antidote

BITTEN by a snake? A DNA test could help find the antidote.

When a snake bites someone, it leaves some of its DNA along with the venom. Now, that can identify the species of snake; a finding that could take the guesswork out of choosing the right antidote.

“At present, the standard of practice is no identification at all, a diagnosis from the symptoms, or more rarely identification of dead snakes that victims occasionally bring to the clinic,” says François Chappuis of Geneva University Hospitals in Switzerland, who presented the work this week at the American Society of Tropical Medicine and Hygiene annual meeting in New Orleans.

Chappuis and his colleagues collected samples from the fang wounds of 749 people at three health centres in Nepal, amplified the DNA and sequenced it. They then looked for matches in a publicly available reference bank of DNA sequences.

They managed to identify the snake responsible for 194 bites, 87 of which were from species whose venom is harmful to people. Chappuis aims to produce fast bedside tests that detect locally dangerous species.

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in Brief

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