Monday, October 1, 2007; A09

Ion-Propelled Craft Launched On Mission to Study Asteroids

An unmanned spacecraft with powerful instruments and a novel propulsion system has begun an eight-year mission to study the two largest objects in the asteroid belt between Mars and Jupiter.

NASA's Dawn spacecraft lifted off from Cape Canaveral on Thursday, beginning a 3 billion-mile, $357 million mission to orbit the rocky asteroid Vesta in 2011 and the icy dwarf planet Ceres in 2015 -- both about 4.5 billion years old. Dawn will gauge their elemental composition, mass and gravitational fields, surface topography and tectonic history, and look for water-bearing minerals.

"Visiting both Vesta and Ceres enables a study in extraterrestrial contrasts," said Christopher Russell, the mission's principal investigator and a geophysicist at the University of California at Los Angeles. "One is rocky and representative of the building blocks that constructed the planets of the inner solar system. The other may very well be icy and represents the outer planets. Yet these two very diverse bodies reside in essentially the same neighborhood. It's one of the mysteries Dawn hopes to solve."

The space probe will power its way there using three novel ion propulsion engines. They use solar-derived electricity to ionize xenon gas and generate thrust. Ion engines are far less powerful than conventional chemical rockets but have one big advantage: They can fire for months at a time.

-- Christopher Lee

Seeing another person subjected to an awful fate -- eaten alive by a shark, say, or jumping from a burning building -- it's difficult not to flinch. This automatic response of empathy is triggered by the activation of a brain circuit that includes regions known as the anterior insula, periaqueductal gray and anterior cingulate cortex.

Scientists in Taiwan and Chicago recently asked a simple question: What happens to that response in the brains of physicians, who inflict pain on patients during medical procedures?

Fourteen physicians and fourteen people who were not doctors recently had their brains scanned as they watched videos of acupuncture procedures. While the non-medical volunteers showed a strong activation of the brain regions involved in the empathy circuit, the physicians did not, according to a study to be published in next week's issue of Current Biology. It was led by Yawei Cheng of Taipei's National Yang-Ming University.

The physicians, instead, showed activation in their prefrontal cortex, in brain areas related to thinking and control of emotions.

"They have learned through their training and practice to keep a detached perspective; without such a mechanism, performing their practice could be overwhelming or distressing, and as a consequence impair their ability to be of assistance for their patients," said co-author Jean Decety, professor in psychology and psychiatry at the University of Chicago.

-- Shankar Vedantam

A prostate cancer treatment often given to men with aggressive forms of the disease may increase tumor cells' ability to spread through the body, a study published today suggests.

The research, led by David Berman of the Johns Hopkins University School of Medicine, sheds new light on a protein called nestin, which is produced primarily in cells during fetal development but also in some tumor cells in adults.

Berman's team studied prostate tissue samples from early stages of the disease and also from late-stage, metastatic disease. They found that nestin was being produced by the metastatic cells but not by the early-stage cells.

That raised the question of whether nestin production is an inherent trait of advanced prostate cancer cells or a result of the treatment given to some men with aggressive forms of the cancer. That treatment, called androgen deprivation, blocks the effects of testosterone, which can feed prostate tumor growth.

When prostate cancer cells growing in laboratory dishes were deprived of testosterone, nestin levels rose. When transplanted into mice, those nestin-producing cells were better able to spread to distant organs than cells not making nestin.

The work, published in the Oct. 1 issue of Cancer Research, suggests that androgen blockers, though they slow tumor growth, may also "encourage the cells to metastasize," Berman said.

-- Rick Weiss