On Curves, Dogs Have the Edge

Humans can't run curves. Just compare the time it takes a sprinter to race 400 meters outdoors, with two turns, and the time it takes on an indoor track half as long with four tighter turns -- the outdoor sprinter is about 11/2 seconds faster.

This is because of the "duty factor" -- runners keep their feet on the ground longer in turns because centripetal force -- counteracting the centrifugal force that tries to push them wider around a turn -- increases their effective weight. Keeping feet on the ground spreads the load. It also slows you down.

It probably comes as no surprise that greyhounds don't have this problem. "They're more like a bicycle," said zoologist James R. Isherwood of Britain's Royal Veterinary College. Front legs, like the front wheel, are "fairly passive" and simply support weight, he said, leaving hindquarters to provide the power.

In a report last week in the journal Nature, a team led by Isherwood studied greyhounds running two straightaways and a curve, and it found virtually no change in the duty factor going around the bend.

The forequarters handle the centripetal load, while the dog maintains speed by torquing its hips and extending its back. Isherwood said that "anything built for running -- horses, cheetahs or greyhounds -- probably has the same advantage."

Knowing that greyhounds don't slow down on curves means that you have to care for them differently. "They need as wide a turning radius as possible," Isherwood said. "Dogs don't make any adjustment" for turns, and the centripetal stresses on the forelegs increase markedly as the turn tightens, increasing the risk of strain and injury.

-- Guy Gugliotta

Gene Puts Motor in Hungry Mice

When yeast, fruit flies and mice get too little food, they tend to live longer. Scientists trying to understand why know that in yeast and fruit flies, at least, a gene called "silent information regulator 2" is involved in this unusual effect.

Researchers at the Massachusetts Institute of Technology have figured out what the mouse version of this gene does. It makes hungry animals more active.

Danica Chen and Leonard Guarente of MIT's biology department created "knockout" mice that lacked the Sirt1 gene. The researchers then measured the daily food intake of the "knockout" mice and a group of normal mice when both were allowed to eat as much as they wanted. Then they reduced their daily feed to only 60 percent of their previous intake and measured the amount of activity in their calorie-restricted mice.

When mammals are on a calorie-restricted diet, they typically increase their activity and foraging behavior. And in fact, the normal animals -- the ones that still had the Sirt1 gene -- greatly increased their activity during nine hungry months at MIT. But the mice lacking the gene either showed no increase in activity or, in many cases, a noticeable decrease.

The researchers also tested the animals' capacity to stay on a treadmill. The knockout mice actually did better than the normal ones -- evidence that lack of Sirt1 hadn't physically disabled them.

The scientists concluded that Sirt1 is involved in turning up an animal's "activity dial" when food gets scarce, a pattern that, in nature, might help it find more to eat. Whether the gene is also involved in determining life span remains to be discovered.

The research, assisted by Andrew D. Steele and Susan Lindquist of the Whitehead Institute for Biomedical Research in Cambridge, Mass., appears in the journal Science.

-- David Brown

Love Hormone Conquers All

Love and trust really can conquer fear and anxiety.

Scientists have long been intrigued by the hormone oxytocin, which plays a role in complex social behavior. The hormone is part of a system in the brain that controls the formation of emotional bonds, and plays a role during sex, childbirth and breastfeeding.

Now, scientists at the National Institutes for Health and Justus-Liebig University in Germany have discovered that oxytocin, which some have dubbed the hormone of love, can make volunteers less fearful. In a paper published last week in the Journal of Neuroscience, researchers found that volunteers who had oxytocin sprayed into their noses had less fear response when shown frightening images than those given a placebo. Volunteers' fear reactions were measured through a very sensitive brain-imaging technique that revealed less activity in the part of the brain known as the amygdala.

Diminished activity in the amygdala has long been linked to increased sociability and decreased fear, wrote the researchers, whose work was funded by the National Institute of Mental Health.

The scientists said the research suggested the possibility of using the hormone to treat serious mental disorders characterized by increased anxiety and fear.

-- Shankar Vedantam

Runners must slow down on curves because of centripetal force . . . . . . but greyhounds use their hindquarters to maintain top speed.