Putting the 'Man' in Salamander

All the Viagra in the world won't help a man if the woman he yearns for is not interested in him. But there is hope. For the first time, scientists have found a chemical compound that increases a female's "receptivity," or the speed with which she will respond to a male's advances.

Unfortunately for men, the compound--secreted from a gland under a male salamander's chin--has been shown to work only on female salamanders.

Males of the land-dwelling salamander Plethodon jordani rub their chin secretions beneath a female's nostrils during a specialized courtship dance known as a "tail-straddling walk," in which the two walk forward together with the female straddling the male's tail while she rests her chin on the base of his tail.

Stephanie Rollmann of the University of Chicago and her colleagues isolated the main component of the glandular secretion, a protein they call plethodontid receptivity factor (PRF). Then the team measured how long it took for females to be wooed by males, whose glands had been removed, when either PRF or salt water was applied to the females' nostrils during the tail-straddling walk.

On average, females dabbed with saline surrendered to the males after 47 minutes, while those dabbed with PRF were overcome by passion after 40 minutes, the researchers report in the Sept. 17 Science.

Rollmann plans to test PRF's effects on other species. But so far, she said, none of her lab mates have tried it themselves.

Fungi's Punching Power

Many plant diseases are caused by fungi, which penetrate the plant's tough outer skin, or cuticle, to feed on the soft and nutritious pulp within. Some of these fungi gain access by secreting cuticle-dissolving enzymes, but others use brute force to punch their way in. Now scientists have measured that battering force directly and have found it to be surprisingly large for a supposedly immobile life form.

A team of physicists and biologists in Germany used a sensitive force-sensing instrument to measure the power with which fungal cells of the species Colletotrichum graminicola can push against a thin aluminum film. In nature, the fungal cells (which cause a disease of corn) adhere tightly to plant leaves, then fill with water taken up from dew drops. As they expand over the course of two hours or so, they press with increasing force against the leaf, ultimately bursting through the cuticle.

The researchers found that the cells can build up astonishing internal pressures of more than 5 megapascals, or about 30 times that found in car tires. That translates into a force of about 17 micronewtons, more than enough to crush the cuticle's cellular architecture.

The work could speed development of crop-protecting fungicides that block the pressure-building mechanism, the researchers report in the Sept. 17 Science.

Lighting the Way to Better CDs

Scientists have created a new kind of laser that emits pure blue light at room temperature, a feat that could lead to the development of compact discs and other information storage systems with much higher capacities than those currently used.

Today's commercial compact disc players produce sounds and visual images by using beams of infrared light to "read" the pattern of microscopic potholes in compact discs and CD-ROMs. Blue laser light has a shorter wavelength than infrared, allowing it to distinguish among potholes that are much closer together. That means a blue-laser CD player could read information packed much more densely on a disc. But until now, blue lasers of the type used for CD readouts worked only in supercold, subzero temperatures.

Researchers in Japan, Germany and Italy have collaborated to make the first "blue vertical cavity surface-emitting laser" that operates at room temperature. The team achieved the feat by improving upon older methods of growing the crystals that act as light-focusing mirrors in such lasers.

The new technology could allow four times as much information to be stored and read on a compact disc, and could drastically increase the readout speed of digital video discs and high-resolution laser printers, the researchers report in the Sept. 17 Science.

Slowing the Brain's Age Decline

Two new studies point to the possibility of slowing the natural decline in brain function that comes with old age.

In one study, reported in the Sept. 14 Proceedings of the National Academy of Sciences, researchers in California found extensive shrinkage of subcortical neurons in old Rhesus monkeys. These brain nerve cells are not the ones usually associated with memory and cognition, but they help coordinate the cortical neurons that are involved in those critical processes.

The team found that by injecting into the monkeys' brains some cells that had been genetically engineered to secrete a nerve growth factor, the atrophied subcortical neurons plumped up and appeared youthful again. Ongoing experiments will tell whether the treated monkeys have better memory than their untreated aging counterparts.

People who don't want to wait until gene therapy is available can consider adding more blueberries to their diets. Researchers in Boston and Denver, working with senior citizen rats, tested the anti-aging effects of meals rich in blueberry, strawberry or spinach extracts-- all of which contain flavonoids, antioxidants that can prevent damage to brain cells. After eight weeks on the special diets, the blueberry group demonstrated a notable reversal of the normal, age-related decline in balance and coordination. And compared with rats on conventional diets, all three groups performed better on memory tests, the researchers report in the Sept. 15 Journal of Neuroscience.