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In brief – used mice with a defective version of a receptor molecule called TrkB, found on the surface of brain cells in the hippocampus. The mice were unable to learn or initiate LTP in response to familiar stimuli, indicating TrkB is a key memory molecule. The finding will be published in Learning and Memory this week. Minichiello hopes that as they identify more molecules involved in initiating LTP, this could pave the way for drugs to combat Alzheimer’s disease, or to enhance memory capability generally. her colleagues at the European Molecular Biology Laboratory in Monterotondo, Italy, and the Pablo de Olavide University in Seville, Spain, appear to have done just that by isolating a molecule that initiates a signalling pathway for LTP in the brain of a living mouse. The finding builds on a technique they developed last year to record LTP in a mouse hippocampus – a brain region involved in learning – while the animal was being trained to blink in response to a tone. In the new study, the team DESPITE its 300-year history, Newton’s gravitational constant, G, is the least well measured of all the fundamental constants. Now quantum mechanics may help pin down the strength of gravity more precisely. Traditionally, various kinds of torsion balance have been used to calculate G by measuring the twist in a wire induced by the gravitational force between two masses. But this can only provide rough estimates. Mark Kasevich of Stanford University in California and colleagues split a beam of caesium atoms into two using an interferometer, then recombined them to produce interference fringes. A 540-kilogram lead weight placed near the beams shifted their paths and the interference pattern. The team used the shift to calculate a value for G, which matched that found by traditional methods (Science, vol 315, p 74). This technique could one day yield the most accurate value of G. “We’re seeing the gravity field in a purely quantum mechanical way, so we’re free of the errors that limit the accuracy of traditional methods,” says Kasevich. Gravity gets a quantum boost Cold facts about ancient eruptions YOU would expect that any evidence of how ancient volcanoes influenced Earth’s climate went up in smoke long ago. Not so. It now seems that traces of past eruptions are locked up in the Antarctic ice, and can reveal if the plumes were massive enough to affect climate. Volcanic particles that enter the stratosphere – the layer of Earth’s atmosphere from about 10 to 50 kilometres up – undergo a distinctive reaction in the presence of intense ultraviolet light, affecting the ratios of sulphur isotopes that are eventually carried down to Earth as sulphate compounds. Mélanie Baroni of Joseph Fourier University in St-Martin- d’Hères, France, and her colleagues studied volcanic particles in ice core samples from Antarctica, a region not contaminated by human emissions. They detected two past eruptions that punched through into the stratosphere: the Philippines’ Mount Pinatubo in 1991 and Indonesia’s Mount Agung in 1963. Both eruptions affected Earth’s climate by blocking out sunlight. Pinatubo is estimated to have cooled Earth by about 0.5 °C. Now Baroni and her colleagues have drilled an ice core that dates back 1 million years, in order to find stratospheric eruptions. “It is helping us to work out the climatic impact these eruptions have,” she says. Barn swallows get broody while world warms WARMER spring temperatures and a longer growing season are proving to be good news for barn swallows. Over the past 35 years these birds have responded to global warming by taking more time over rearing their chicks. Around two-thirds of swallows produce two broods of chicks per year, one in April and another in July or August. Anders Møller from the Pierre and Marie Curie University in Paris has monitored barn swallows in the Kraghede region of northern Denmark since 1971, noting the date eggs were laid, and clutch and brood size. Based on 2705 pairs of birds, Møller found that the time between clutches increased between 1971 and 2005. The birds started to breed earlier and gave themselves more time before the second brood. Timing between clutches increased by an average of 8 days (19 per cent) and swallows tended to produce more fledglings (Behavioral Ecology, DOI: 10.1093/beheco/arl051). Møller believes that this relaxed breeding behaviour is down to climate change. Between 1971 and 2005 the mean April temperature in Denmark rose by 2.2 °C. The growing season, too, is longer. “The [temperature] changes we are seeing today are much more rapid than in the past and the question is whether these birds will be able to keep up,” says Stuart Bearhop, an ornithologist at the University of Exeter, UK. HOW are memories formed? The question has perplexed scientists for years, but now it seems we’re a step closer to solving it. The leading candidate is a process called long-term potentiation (LTP), in which the connections between individual brain cells get stronger the more often they are used, such as during learning. But while LTP has often been observed in slices of brain in the lab, it has been difficult to record in a living brain as learning was taking place. Now Liliana Minichiello and PAUL VAN GAALEN/ARDEA R.S. CULBERT/USGS Memories are made of this molecule… 16 | NewScientist | 13 January 2007 www.newscientist.com
