12 | NewScientist | 24/31 December 2011

Why mole rats feel no pain from acid

DROP acid on a naked mole rat and it won’t flinch. The secret behind its insensitivity to acid pain could help treat arthritis.

Naked mole rats, like most animals, carry special acid-activated channels at the tips of sensory neurons called nociceptors. The channels transmit a pain signal if exposed to acid. But the nociceptors also contain another type of channel – called NaV1.7 – which become blocked when exposed to a certain amount of acid, dampening the pain signal.

Ewan Smith and colleagues at the Max Delbrück Center for Molecular Medicine in Berlin, Germany, doused nociceptors from naked mole rats and mice in acid, and found the strength of the pain signal passing through the NaV1.7 channels dropped significantly more in the mole rats.

“The acid block of NaV1.7 is so strong that the simultaneous activation of acid sensors is irrelevant and no signal is conducted,” says Smith (Science, DOI: 10.1126/science.1213760).

The equivalent sodium channel in humans could be a target for preventing the pain caused by acid build-up, a symptom of arthritis.

Window into stealth tactics of bacteriaWE ARE now privy to the ways bacteria outsmart antibiotics, thanks to a technique which measures the evolution of antibiotic resistance.

A team led by Erdal Toprak and Adrian Veres at Harvard University developed the “morbidostat”, a device that constantly monitors the growth of bacteria in the presence of an antibiotic, increasing the concentration of the drug as the bacteria evolve resistance.

Using the morbidostat, the team investigated how Escherichia

coli responded to three different antibiotics over 25 days.

Levels of resistance increased for all three drugs. However, resistance to chloramphenicol and doxycycline developed smoothly over time, whereas resistance to trimethoprim happened in discrete steps.

The team sequenced the genome of E. coli from the final stage of the experiment. Bacteria resistant to chloramphenicol and doxycycline had a large number of changes all over their genome, suggesting that lots of small

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mutations outsmart the drugs. For trimethoprim resistance, most changes took place in just one gene. The bacteria had to wait for mutations to occur in this small area, which explains why resistance evolved in stages.

Further sequencing revealed the same mutations occurring in the same order in every trimethoprim-resistant population (Nature Genetics, DOI: 10.1038/ng.1034). Knowing about these pathways of resistance could help to find drug doses to minimise resistance.

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SOMETHING has moved boulders on Mars, causing curious clumps near the northern ice cap. Now it seems the culprit is not Martians, but winter.

You would expect boulders to be randomly sprinkled across the Martian surface. But images from NASA’s Mars Reconnaissance Orbiter showed them clustered at the edges of polygon-shaped cracks in the soil. A team led by Travis Orloff at the University of California, Santa Cruz, suggests what may have moved them.

The polygons are thought to contract and expand each winter and summer. The boulders are encased in

a layer of carbon dioxide frost during winter. As winter progresses, heat from the soil vaporises the bottom of this icy layer, detaching it from the ground. The rest of the icy slab holds the boulders in place as the underlying polygons shrink. In summer, heat from above the slab vaporises it and dumps the boulders back on the ground. The boulders are now closer to the edges of the polygons than they were before. The process then repeats itself each year.

Orloff presented the suggestion at the American Geophysical Union meeting in San Francisco, California.

Icy hand of winter moves Mars rocks

The brainiest legs in the world

TINY body, big problem: minuscule spiders need fairly sophisticated brains to weave their webs, but how do you cram that circuitry into such an itsy bitsy body? If you’re as small as Anapisona simoni, you don’t – your brain spills into your legs.

Juvenile forms of tiny spiders such as A. simoni tip the scales at less than 5 micrograms, but have the web-weaving smarts of much larger arachnids, says William Eberhard of the Smithsonian Tropical Research Institute in Panama and the University of Costa Rica.

With colleagues, Eberhard has documented the neuroanatomical consequences of that web-spinning brainpower. They found that about 80 per cent of the head and thorax of A. simoni spiderlings is taken up by brain. Remarkably, the micro-spiders’ brains even extend into their legs (Arthropod Structure & Development, DOI: 10.1016/ j.asd.2011.07.002).

It’s a mystery how the juveniles find enough space for digestive tissue to feed their hungry neurons, says Eberhard. “These little animals are sort of against the wall,” he says.

A. simoni is not the only animal to indulge its brain this way. The brains of some tiny insects extend into the abdomen, while miniature salamanders have sacrificed bones from their skulls to free up room for their brains.

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