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gen. Previous tests had found that bisphenol-A can leach into food and water and that it’swidely prevalent in human blood.

The newfound contribution of the chem-ical to insulin resistance, a precursor to dia-betes, might partially explain the global epi-demic of that disease, says Angel Nadal ofMiguel Hernández University of Elche inSpain, who led the new study.

The finding is a “wake-up call” for pub-lic health researchers who are concernedby the prevalence of diabetes, commentsdevelopmental biologist Frederick vom Saalof the University of Missouri–Columbia.

Earlier test-tube studies had suggestedthat bisphenol-A makes pancreatic cellssecrete the glucose-regulating hormoneinsulin. To investigate this effect in live ani-mals, Nadal and his colleagues injectedadult male mice with pure corn oil or withoil containing either bisphenol-A or anequal amount of the natural female sex hor-mone estradiol. Animals received as manyas eight shots over 4 days.

Within 30 minutes of an injection, ani-mals receiving either the sex hormone orbisphenol-A had abnormally low concen-trations of glucose in their blood, Nadal’steam reports in the January Environmen-tal Health Perspectives. The chemicals actedon recently discovered estrogen receptorson pancreatic cells’ surfaces to boost thecells’ secretion of insulin, the researchersdetermined.

Repeated exposure to either bisphenol-Aor the natural estrogen over several daysproduced insulin resistance, a pre-diabeticstate in which tissues lose their sensitivityto normal concentrations of insulin, Nadal’sgroup says. Estrogen receptors in the pan-creatic-cell nucleus appear to contribute tothis gradual effect.

So, receptors both in the cell nucleus andon the surface could contribute to insulinresistance and diabetes, Nadal says.

This risk could add to or elucidate alreadydocumented health effects of bisphenol-A.Animal studies have suggested that expo-sure to the chemical early in life causes obe-sity, says Ana M. Soto of Tufts UniversitySchool of Medicine in Boston.

Furthermore, bisphenol-A exposure mightcontribute to gestational diabetes in women,in whom insulin resistance often increasesduring pregnancy, says Jerry Heindel of theNational Institute of Environmental HealthSciences in Research Triangle Park, N.C.

Inside cells’ nuclei, bisphenol-A is lesspotent than the natural sex hormone, saysvom Saal. But the new work shows that atthe surface of pancreatic cells, the com-pounds have the same potency, he notes.Doses of bisphenol-A considered by theEnvironmental Protection Agency to haveno adverse effect led to insulin resistancein the mouse study. —B. HARDER

Intrinsic Remedies for PainPlacebo effect may takevarious paths in brain

The brain draws on a range of pain-fight-ing options when people receive sham treat-ments for pain, a new brain-imaging studysuggests.

People who experienced pain relief afterreceiving fake acupuncture treatments dis-played pronounced activity in certainbrain areas, says a team led by neurosci-entist Jian Kong of Massachusetts Gen-eral Hospital in Charlestown. This patternof brain activity differed from thatreported in 2004 by another team,directed by neuroscientist Tor D. Wagerof Columbia University.

In that work, a placebo cream appliedto the skin diminished pain. In both exper-iments, the researchers induced volunteers’pain by applying heat to the forearm.

“There may be multiple brain mechanismsunderlying placebo [pain relief],” Kong says.He and his colleagues describe their findingsin the Jan. 11 Journal of Neuroscience.

Kong’s group established the pain toler-ance of 16 volunteers, ages 22 to 35. Using adevice that delivered heat to the right fore-arm, the scientists noted how much heat wasneeded to yield ratings of low or high pain.

Volunteers then read information aboutacupuncture before receiving on their rightarms a sham acupuncture treatment thatthey had been told was real. The placeboacupuncture needle retracted into its cas-ing when pressed against the skin. Toencourage expectations of the shamacupuncture’s effectiveness, without tellingthe volunteers, the researchers slightlydecreased the temperature of ensuing heatpulses delivered to participants’ right arms.

Next, a functional magnetic resonanceimaging scanner measured blood flowthroughout volunteers’ brains as low- andhigh-pain heat pulses were delivered totheir right or left arms.

A placebo effect emerged. Individualsreported feeling substantially less pain intheir right arms than in their left arms dur-ing delivery of equally intense heat. Placeboresponses were accompanied by pro-nounced blood flow, a sign of intense neu-ral activity, in six brain regions, the scien-tists say. These areas regulate painperception, monitoring of external events,and negative emotions such as anxiety.

In contrast, Wager’s team linked placeboresponses to diminished activity in pain-sensitive regions overlapping those identi-fied in Kong’s study.

Wager points out that Kong’s team meas-ured elevated activity in pain-related brainregions shortly after volunteers started tofeel pain, whereas his team looked at a laterphase of pain. Neural activity in affectedregions diminishes as pain continues, hisstudy indicated.

However the brain orchestrates sucheffects, positive expectations can evenreduce pain controlled by spinal cord sig-nals, say neuroscientist Dagfinn Matre ofthe National Institute of OccupationalHealth in Oslo and his colleagues.

Earlier research had shown that nerveprojections from the spinal cord create tem-porary, extreme pain sensitivity in heated-skin areas. To produce that effect, the sci-entists delivered heat pulses to the rightforearms of 29 volunteers for 5 minutes.

The right forearms of 19 of the volun-teers were then heated by an instrumentcontaining a sham magnet that they hadbeen told was a pain-relieving device. Thoseparticipants reported a smaller area of painand less pain overall than those who didn’t

Streaking through Earth’s atmosphereafter a 7-year, 5.6-billion-kilometer jour-ney, a space capsule carrying comet

and interstellar dust landed in the Utahdesert on Jan. 15. NASA’s Stardust space-craft collected its most precious cargo 2 years ago, when the craft passed within24 km of the dust-venting nucleus ofComet Wild-2 (SN: 7/3/04, p. 13). Scientistsexpect the dust to provide new clues tothe solar system’s origin because cometsare nearly pristine relics of that time.

The tiny dust grains are the first sam-ples of solid extraterrestrial material tobe collected and brought back to Earthsince the last moon rocks arrived in1972. A craft bearing gaseous samples ofthe solar wind crashed when it returnedto Earth in 2004. —R. COWEN

Pay DirtCometary dust collector comes home

SPECIAL DELIVERY Comet dust–bearingcapsule after it landed in the Utah desert.

NA

SA

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expect pain relief, the researchers report inthe same issue of the Journal of Neuro-science. —B. BOWER

ThermonuclearSqueezeAltered method extendsbubble-fusion claim

A technique that some scientists claim gen-erates thermonuclear fusion in a benchtopapparatus works even without its contro-versial neutron trigger. So say the researcherswho, since 2002, have reported that nuclear-fusion reactions can occur in a vat of chilledsolvent agitated by ultrasound (SN: 3/6/04,p. 149). If this method of sparking fusionproves to be valid—a big if, critics insist—itcould lead to a remarkably simple, cheap,inexhaustible power source.

Fusion reactions take place in the vatbecause clusters of bubbles form and thenviolently collapse, explains nuclear engineerand team leader Rusi P. Taleyarkhan of Pur-due University in West Lafayette, Ind. A neu-tron or another energetic particle triggers abubble to form in a low-pressure trough ofthe ultrasound waves, he says. Then, highpressure from the wave crushes the orb toan enormous density and temperature thatfuse some atomic nuclei of the bubble’s gas.

Taleyarkhan and his colleagues havemeasured neutron emissions as a sign offusion reactions. Because the group hadused neutron pulses to trigger the process,other researchers have been skeptical of itsneutron readings.

In an upcoming Physical Review Letters,Taleyarkhan’s team presents evidence offusion in bubbles initiated by a uranium-based trigger that emits alpha particlesinstead of neutrons. “We got away from theidea of using neutrons to produce neutrons,”Taleyarkhan notes.

Nonetheless, the findings still face intenseskepticism. Criticisms range from doubtsabout experimental procedures to quarrelswith interpretations of the data. “I simply donot find the results significant and/or believ-able,” comments physicist Dan Shapira ofOak Ridge (Tenn.) National Laboratory.

Critics note that Taleyarkhan’s teamadmits in its report that its experimentaloutcomes vary greatly, many of them pro-ducing no evidence of fusion. Yet to D. FelipeGaitan of Impulse Devices in Grass Valley,

Calif., the uneven outcomes are encourag-ing. They “could explain our inability, andthat of other researchers so far, to replicate[Taleyarkhan’s] results consistently,” saysGaitan. Impulse Devices plans to commer-cialize bubble fusion.

Lawrence A. Crum of the University ofWashington in Seattle says that the new work“increases the credibility” of bubble fusion.But “unless it’s reproduced in someone else’slab, I’m not going to believe it,” he adds.

Taleyarkhan claims that his team’s find-ings were independently verified last yearby other Purdue researchers, whom heguided. Other physicists are unconvinced.

A welcome consequence of the latestresults, Crum adds, is that other re-searchers should find the uranium-basedtriggering method easier to reproducethan the neutron one. So, he says, the newwork “is an important step toward deter-mining if the results of Rusi’s experimentsare true.” —P. WEISS

Sinking MercuryLight-based reactionsdestroy toxic chemical in Arctic lakes

Sunlight triggers the entry of poisonousmercury into polar lakes, but it also removesmost of the toxic compound before fish canconsume it, a new study suggests. Theresearchers warn that increased warming inthe Arctic might upset this delicate balance.

With spring, light returns to the Arcticafter a long, dark winter. That polar sunrise,however, has a dark side. It triggers a burstof photochemical reactions that mobilizesatmospheric mercury, speeding its fall intoarctic lakes, where fish can consume it.

Recent studies suggest that when atmos-pheric mercury encounters light, gases suchas ozone and sea spray–borne halogens oxi-dize it to a more reactive and water-solubleform. Attached to rain, snow, or dust, thereactive mercury falls into oceans or lakes,where sulfur-reducing bacteria transformit to methylmercury, the highly toxic formof the metal that accumulates in fish andother organisms (SN: 2/1/03, p. 72).

To better understand what happens tomercury, a team of researchers led by bio-geochemists Chad Hammerschmidt ofWoods Hole (Mass.) Oceanographic Insti-tution and William Fitzgerald of the Uni-versity of Connecticut at Groton studiedmercury in four Alaskan lakes roughly 250kilometers south of the Arctic Ocean.

The team measured mercury entering thelakes from rainfall and as runoff from thesurrounding tundra and then estimated howmuch methylmercury the bacteria in the lake

sediments subsequently produced. Theresearchers also assessed whether themethylmercury was consumed by fish andother creatures or converted to less-toxicforms by light-based reactions in the lakes.

Hammerschmidt and his colleaguesreport that the more atmospheric mercuryrains down, the more methylmercury thebacteria produce. Two-thirds of mercury inthe atmosphere comes from human sources,such as fossil fuel burning, so more pollutionwould boost poisonous mercury concentra-tions in lakes, Hammerschmidt says.

More unexpectedly, the team discoveredthat light-triggered breakdown of methyl-mercury in the clear Arctic lakes is the mainfactor keeping the poison in check. Thosereactions destroy as much as 80 percent ofthe poison before aquatic species can get toit, the team reports in an upcoming Envi-ronmental Science & Technology.

The mechanisms of that photodecom-position are still poorly understood, Ham-merschmidt says. Research on arctic mer-cury has focused on how it gets to Earth,rather than its terrestrial fate, he says.

This research is the first to demonstratethe importance of photodecomposition inmercury cycling, agrees Robert Stevens ofthe Environmental Protection Agency inResearch Triangle Park, N.C. “It’s good sci-ence,” he says.

One spur to further study is the possibil-ity that global warming could upset the Arc-tic’s delicate balance. In warmer and wetterweather, more mercury would fall and bac-terial production of methylmercury wouldrise. At the same time, the rains might washmore organic material into lakes and oceans,reducing light penetration.

Hammerschmidt cautions that the sameprocesses may also be occurring in tem-perate lakes, such as those in Wisconsin orMinnesota. —C. GRAMLING

SCIENCENEWSThis Week

LIGHT CLEANING Photochemicalreactions in clear Arctic lakes prevent toxicmethylmercury from poisoning fish andother aquatic life. FI

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