3 October 2009 | NewScientist | 17

LEAVING the safety of mother’s care and learning to make your own way are key to growing up. How rat pups make this transition is now becoming clearer.

A team led by Regina Sullivan of New York University’s Langone Medical Center previously found that young pups are attracted to odours even when those smells are paired with electric shocks. Only at about 10 days old do pups learn

to link odours to negative stimuli. Sullivan also found that odours associated with mother initially suppress the release of the stress hormone corticosterone in pups.

Now her team has shown that this suppression reduces levels of the neurotransmitter dopamine in the amygdala, the brain’s “fear centre”. Dopamine-linked genes, which were relatively inactive in 8-day-old rat pups exposed to

Roof meadows cut carbon overheads

GREEN roofs are not just a load of greenwash. That’s according to a new study which has measured the amount of carbon absorbed by 13 different green roofs.

Kristin Getter of Michigan State University in East Lansing and her colleagues found that the roofs absorbed up to 375 grams of carbon per square metre over the two years of their study.

That may not sound like much, but it adds up. If every roof in a city the size of Detroit, Michigan, with around a million inhabitants, were a green roof, it would remove as much carbon from the atmosphere each year as taking 10,000 mid-sized SUVs off the road.

There’s a catch, though: if you grow a green roof, you need to keep it up there for a long time. It takes seven years for the roof to offset the carbon used for its building materials and become truly carbon negative.

Feathered dinosaur is older than the earliest bird

THE record for the oldest feathered dinosaur, which has

stood since the discovery of Archaeopteryx, has finally

fallen to an even older fossil unearthed in China. The find

has already shed new light on the origin of birds.

Spectacular feathered dinosaurs discovered in the last

decade or so show clearly how a small group of theropod

dinosaurs gave rise to the first birds, but these specimens

are nearly all Cretaceous in origin, at least 20 million

years younger than Archaeopteryx. Feathered dinosaurs

pre-dating Archaeopteryx have remained elusive, largely

because the Jurassic theropod fossil record is so poor.

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How rats learn ‘once bitten, twice shy’ shock-paired odours, became more active when the pups were given corticosterone. These pups also learned to avoid the odours (Nature Neuroscience, DOI: 10.1038/nn.2403).

Rats are born helpless, so their initial maternal attachment is vital, but later, learning about danger is important. If similar mechanisms operate in the brains of human infants, it may help explain why they remain strongly attached even to abusive mothers.

Enter Anchiornis huxleyi. It comes from the Tiaojishan

formation of Jianchang county, dated to between 161

and 151 million years old and therefore older than the

150-million-year-old Archaeopteryx-bearing German

rocks (Nature, DOI: 10.1038/nature08322).

Anchiornis possesses well-developed feathers on

all four limbs, and comes from a “critical stage along the

line to birds”, says Xu Xing of the Institute of Vertebrate

Paleontology and Paleoanthropology in Beijing.

“Probably the evolution of longer and stronger fore

wings [ultimately] made the hind wings unnecessary.”

It is unclear, however, whether Anchiornis could fly.

It has unusually long legs, suggesting it might have been

able to run fast, though the long leg feathers could have

made rapid movement difficult.

LACK of sleep could accelerate the onset of Alzheimer’s disease by encouraging toxic plaques to develop in the brain.

Beta-amyloid protein is found in the brains of mice and humans. It causes the build-up of plaques, which some researchers think cause Alzheimer’s by killing cells.

David Holtzman of Washington University School of Medicine in St Louis, Missouri, and colleagues found that beta-amyloid levels were higher in mouse brains when the mice were awake than when they were sleeping.

Sleep deprivation also caused more plaques to develop, while an insomnia drug reduced the amount of plaque-forming protein (Science, DOI: 10.1126/science.1180962).

Sleep away the troubles of age

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