lions and threatening human health. ’Iko tained within a dialysis sac, the larvae died - SCIENCE NEWS This Week

tern. Instead of directly blocking ghrelin’s hunger-inducing actions, physicians might use PYY3-360r mimics of it to curb appetite.

Ghrelin and PYY3-36 “are roughly equally potent. One increases food intake by about a third; the other decreases it by about the same amount,” says Bloom.

In the 1970s, scientists found Pn3-36 in pig intestines. Bloom and other investigators subsequently discovered that the small and large intestines of people secrete Pm3-36 into the blood after every meal in amounts proportional to the caloric content of a meal. In the 198Os, the researchers injected the protein into people to study its effects on stomach actions such as acid secretion.

’We didn’t think to look at appetite,” says Bloom.

In the new work, the researchers found that the hormone prevents specific brain cells from secreting a potent appetite- inducing chemical signal. They also iden- tified the brain-cell-surface protein that PYY3-36 acts upon, a potential target for drugs mimicking the gut hormone. Scien- tists will probably seek an oral drug, since Pw3,(j must be administered by injection.

To reveal all the hormone’s roles, Bloom’s team is creating genetically engineered mice that lack Pm3-36. “It seems to be a postdi- gestive hormone, switching off appetite, delaying the emptying of the stomach because enough food has gotten into the intestines, and inhibiting acid secretion because you finished eating and no longer need it,” he says.

The range of findings that Bloom and his colleagues present impresses David E. Cummings of the University of Washing- ton in Seattle, who studies ghrelin. In asin- gle report, he says, they’ve shown appetite suppression by the hormone in both rodents and people and described the brain pathway by which Pn3-36 appears to work.

Still, Cummings notes that other putative satiety factors have generated excitement but failed to develop into a viable drug for obesity. ’We’ve been down this road before,” he cautions. -J. TRAVIS

pfsesteria’s Bite Microbe may kill fish by skinning, not poisoning - Arguments have taken a strange turn over how to isolate toxins from the Pfiesteria microbes mused of killing fish by the mil-

research teams now say that in the PJieSte- ria strain they’ve examined, there’s no toxin tohd . Instead, explains one ofthe -,the single-celled dinoflagellate alga kills by

rapidly even though they had no direct con- tact with the algae. Burkholder adds that the chemists with whom she works have found a toxin.

swarming over afish and eating a&yits skin. The two new papers join other recent A laboratory sample of Pfiesteria worktosuggestthatfears ofPJieSteriahave

shumwayae, one of two named Pfiesteria been overblown, says Wayne Litaker ofthe species, slays National Oceanic and fish only by Atmospheric Adminis- direct contact, tration in Beaufort, N.C. says Robert He’s seen PJieSteriu feed- Gawley of the ing directly on fish in University of laboratory tanks, but he Miami in Coral cautions that wild, free- Gables. By swimming fish may centrifuging a avoid lethal densities of solution of these algae. P. shumwayae Some 40 other men- growing in the aces-from low oxygen lab, the scien- concentrations to a tists removed THE FIAYER? A mobile stage of the alga water fungus-can give the microbes Hiesterla shumwayae can nibble a flsh to death. fish bleeding skin from the mix. ulcers, Litaker says. In The leftover liquid, which would contain any released poisons, proved harmless, Gawley‘s team reports in an upcominghceedings of the NationalAcademy of Sciences.

Results from other tests prompted the same conclusion from Wolfgang Vogelbein of the Virginia Institute of Marine Science in Gloucester Point and his colleagues. They report that fish stayed healthy when bathing in the same liquid as P. shumwayae, as long as filters prevented direct contact.

Also, microscope images of fish in con- tact with l? shumwayae showed algal cells gouging the fish’s skin, Vogelbein’s team reports in an upcoming Nature.

Debates over P$esteria biology have heated up since 1992 when JoAnn Burk- holder of North Carolina State University at Raleigh and her colleagues blamed this genus for filling North Carolina rivers with dead fish with bloody skin ulcers (SN: 9/6/97, p . 149). In the late 199Os, alarm rose that breathing spray from w- ateria-laden waters, in the lab or outdoors, impairs people’s mental functioning.

Gawley says that when he started his cur- rent work, he intended to find the toxins causing such havoc. Besides testing cen- trifuged samples, his team looked for genes encoding enzymes that other dinoflagel- lates seem to use to make toxins, but none turned up in I? shumwayae.

Vogelbein and his colleagues tested the same strain of P. shumwayae that Gawley did. “The only time we saw fish dying was when they were in contact with the Pfies- tm’a,” says Vogelbein’s collaborator Jeffrey Shields of the Virginia institute.

Burkholder criticizes both papers for not using a sufficiently toxic strain of weste- ria. The ones in her lab knock out the fish much faster, within a few hours instead of a day or two. She says that when her team exposed shellfish larvae to westeria con-

June, his lab reported a 7-stage lifecycle for Pjksteria, instead of the unusually complex sequence of more than 20 stages that Burk- holder has described.

Litaker says that the microbe once seen as an extraordinary poisoner may turn out to be just “a normal, everyday dinoflagel- late.”-S. MlLlUS

Sunlight

Energy trackers gauge water vapor’s wild dance - Despite decades of study, climatechange researchers still can’t tell what in Earth‘s atmosphere is responsible for up to 30 per- cent of the solar radiation soaked up there. Some scientists argue that watervapor-the atmosphere’s major sunhght absorber-takes in much more solar radiation than has been indicated by measurements and models.

Vapor doesn’t absorb enough radiation to explain the discrepancy fully, suggests a newly reported experiment from the hole Polytechnique FkdCrale de Lausanne (EPFL) in Switzerland.

Andrea Cdegari and his colleagues made unprecedented measurements of a property ofvigorously vibratingwater molecules. That property, the extent of the molecules’ charge separation, is closely related to the amount of light energy those agitated molecules can absorb. Charge becomes sepaxated in water molecules because oxygen and hydrogen atoms don’t share electrons equally.

The team’s findings indicate that the actual values of water vapor’s capacity to absorb sunlight should be within about 10 r“ percent of the theoretical calculations to s

84 AUGUST 10, 2002 V O L . 1 6 2 S C I E N C E N E W S