Bear Bones Research; Excremental Progress; If a Neuron Fires in the Woods...

Bear Bones Research Courtesy of Nova Scientists interested in fending off bone degradation have looked to one of the animal kingdom's most naturally gifted bone preservationists: the black bear. Researchers at the Pennsylvania State University recently investigated the ability of Ursus americanus to maintain bone integrity despite extended activity-free hibernation (S.W. Donahue et al., "Serum markers of bone metabolism show bone loss in hibernating bears," Clin Orthop, 408:295-301, March 2003). The researchers analyzed known markers of bone formation and bone loss in blood serum collected before and after hibernation. Normally, human bone loss is indicated by an increase in resorption and a decrease in bone formation. During hibernation, the bears showed increased resorption markers, but no change in formation markers. "They're showing increased loss and same levels of formation. So, there's some subtle suggestion that they're doing something different," says senior author Henry J. Donahue, a professor of orthopedics and rehabilitation. Bears just emerging from their dens, however, showed dramatic increases in the marker for formation, suggesting they're regaining bone much faster than other animals, including humans. Lead author Seth Donahue (no relation), now an assistant professor of biomedical engineering at Michigan Technological University in Houghton, is attempting to bolster the findings by examining other markers of bone turnover in a larger number of bears. --Eugene Russo Excremental Progress With increasing regulatory pressure from European governments to decrease pollution produced on poultry and swine farms, Danisco Animal Nutrition in the United Kingdom and Diversa of San Diego are making it their number one priority to reduce the phosphorus content in animal excrement. Diversa recently received approval from the US Food and Drug Administration for Phyzyme XP, an animal feed addi-tive that will boost intestinal absorption of phosphorus, thus decreasing the amount contributing to pollution. Howard Simmins, Danisco's director of swine research and development, says that Phyzyme is a more efficient form of phytase, an enzyme that breaks down indigestible phytic acid (phytate) found in grains and oil seeds, releasing phosphorus and calcium for digestion. Farmers give extra phosphorus in mineral form to promote bone growth and general well-being of the animals. "It's a bit silly ... [because] it's all coming out the back side," says Simmins. Despite the silliness, Phyzyme won't replace mineral supplements, which are well absorbed, because the animals' needs won't be met through the feed. Phosphorus has outstanding fertilizing properties, but when produced in highly concentrated amounts, it threatens to pollute water supplies. Simmins says that Phyzyme will help maintain an appropriate distribution of phosphorus. "In the end, there will always be enough [phosphorus] to be released into the soil; we're just controlling it in terms of volume." --Hal Cohen If a Neuron Fires in the Woods ... Anne MacNamara Jack Cowan, a University of Chicago math professor, is taking a new view of neural activity--based on forest fire dynamics. In 1990, late Danish theoretical physicist Per Bak described self-activating systems, a system that perpetuates itself such as a fire spreading in self-contained spiral movements. About 30 years ago, Cowan had proposed a three-state neural model of brain function: A neuron builds up to a pulse, then pulses, and finally recovers. Seeing Bak's work, the feedback in the system reminded Cowan of his own model. "There was a parallel between the activity of a neural net and forest fires for many years, from the early days of neural network study in the 1950s," Cowan recalls. So he started doing computer simulations of neurons firing in quick, clustered bursts. To graduate student Tanya Baker, the pattern resembled the pulsating movements of a jellyfish: a sort of localized undulation. When they added inhibitions or excitations to the simulations, modeling what might happen to neurons, the "jellyfish" moved in more directed patterns. The scale of the simulated neural behavior is too small to image, but Cowan speculates that the real thing, if it exists, may be altered in pathological states, such as epilepsy. "What we do is to make models and do the math, and see what the system is telling us about the real nervous system," he says. --Ricki Lewis

Bear Bones Research; Excremental Progress; If a Neuron Fires in the Woods...

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