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Brain food

A new study suggests that mammals may learn best on an empty stomach—and its main author, Tamas Horvath of the School of Medicine, believes that it’s no coincidence. Horvath speculates that the link between fasting and learning may reflect something profound about the origins of intelligence itself.

The key player here is ghrelin, a hormone produced by the stomach when it is empty. Ghrelin can pass from the blood into the brain and is known to regulate energy balance and the release of growth hormone. Horvath’s study, published online on February 19 in Nature Neuroscience, showed that ghrelin enhances spatial learning and memory.

In the research, mice navigated a maze designed to measure how effectively they retained knowledge gained from their explorations. Those injected with ghrelin beforehand performed better than a control group. In another experiment, some mice were injected with ghrelin after undergoing a training task in which they learned how to avoid electrical shocks. Again, ghrelin improved memory retention.

Finally, Horvath’s team experimented with a strain of mice whose learning and memory capabilities deteriorate with age in a way similar to that of humans with Alzheimer's. Ghrelin injections rapidly reversed memory impairment in these mice.

Brain dissections showed that ghrelin promotes synaptic connections between nerve cells in the hippocampus—an area strongly associated with memory and learning. The work may illuminate one reason why obese adults are more likely than others to suffer from memory-impairment diseases like Alzheimer's; indeed, obesity has been associated with decreased ghrelin levels. Horvath hopes his study will help lead to new treatments for dementia and memory deterioration. 

And he goes further. Since the stomach produces ghrelin when it’s empty, he suggests, it may be that when the gut recognizes a need for sustenance, it produces a hormone that increases the brain’s ability to find it. Horvath believes much of our intellectual capacity is an outgrowth of this process. Human cognition, he suggests, might simply be “an offshoot—a side effect of the basic need to be intelligent enough to find your food.”


Life after copper

According to the most sophisticated analysis of metal ore use and reserves ever performed, society could be starting to run short of copper and other critical commodities. But cheer up, says industrial ecologist Thomas Graedel, co-author of the study; doomsday is not necessarily close at hand.

Graedel, of Yale’s environment school, collaborated with geophysics professor Robert Gordon and others for a study that looked beyond extraction and consumption rates, the standard variables in such work. Their analysis, published in the January 31 Proceedings of the National Academy of Sciences, also examined the impacts of changing technologies and resource recovery techniques such as recycling—factors that can make resources last much longer.

Graedel and Gordon focused on copper, zinc, and platinum, metals about which much is known and that play significant roles in the economies of developed societies. They calculated the remaining resource in the ground, the stock of metal currently in use, and the amount already in landfills and otherwise wasted. They then compared the rate of discovery of new ore with the rate of increase in the stock-in-use. “That,” says Gordon, “tells you where you are.”

They found that, if all nations were to use the same services enjoyed in developed nations, even the complete extraction of all metals from the planet’s crust and extensive recycling programs might not meet future demand. Shortages could begin in the next two to three decades.

“We are trying not to adopt the Chicken Little approach,” says Graedel. Changes in the way people use metals—including increased efficiency, expanded resource recovery efforts, and substitution of more-abundant materials—should prevent near-term catastrophic shortages. Indeed, running out is unlikely, he says, “given price escalation as scarcity becomes evident.”


Right-leaning gastropods

For marine snails, it’s a right-handed world. The vast majority of common oceangoing gastropods, such as whelks and cone shells, are righties: that is, when you hold the shell with its apex pointing upward and look at its opening, the opening will be on your right. But on rare occasions, the pattern is reversed, giving rise to left-handed individuals and, rarer still—only about 19 times in the past 65 million years—left-handed marine species.

Several years ago, Geerat Vermeij '71PhD, a University of California-Davis expert on mollusc evolution, dismissed left-handedness as an aberration “without apparent survival function.” But in a paper published in the March edition of the journal Biology Letters, Gregory P. Dietl, a post-doctoral research fellow in geology and geophysics at Yale, revealed an advantage for the leftists: relative immunity from being eaten by crabs. Most crabs, it seems, are right-handed.

Dietl and University of Kansas paleontologist Jonathan Hendricks came to this conclusion by examining fossilized right- and left-handed cone and whelk shells in Florida for scars made by crabs trying to crack the shells open. In fossil samples from 10 of 11 locations, the overwhelming majority of scars were on right-handed snails.

Dietl and Hendricks also studied live box crabs in action against right- and left-handed snails. “The crabs have a specialized tooth on the right claw, which they use as a kind of can opener,” says Dietl. “It’s very effective for opening righties.” It doesn’t work, however, for lefties. The crabs that tried cracking the shells of left-handed snails soon dropped them uninjured and moved on to righties.

“I was surprised by this work,” says Vermeij. “I had concluded that being left-handed didn’t matter, but their data speak louder than my preconceptions.”

Given its apparent advantage then, why is left-handedness so unusual? An entirely left-handed species of whelk exists off the coast of Florida, but few other examples are known. Dietl suggests that the genetic mutation required to change a snail’s coiling direction may be uncommon to begin with, and, to compound matters, lefties and righties may not be able to mate successfully. The required chance meeting between two lefties is highly unlikely.

In most species, then, the lefties live to riper-than-average old age but never have the opportunity to pass their advantageous orientation along to offspring. And consequently, the crabs never feel any pressure to evolve a left-handed can opener. 


For new blood vessels, just add gel

Custom-made human organs and tissues are the stuff of science fiction. But Erin Lavik, an assistant professor of biomedical engineering, recently took an important step towards making them a reality. In the February 21 issue of the Proceedings of the National Academy of Sciences, Lavik and her collaborators reported that they'd grown long-lasting networks of blood vessels in lab mice.

The team created the vascular networks in a polymer-based hydrogel, a Jell-O-like substance, which they had engineered with a specialized internal pore structure that could facilitate capillary growth. “One of the cool things about working with polymers is that if you create a physical architecture, cells will often follow it,” Lavik says.

Her team tried two approaches. In one, they seeded the hydrogels with blood vessel cells alone; in the second, inspired by earlier research, they used both blood vessel cells and neural progenitor cells—stem cells that, in the right environment, can develop into neurons and supporting cells. The gels were then implanted into mice.

Four weeks after implantation, the hybrid approach didn’t appear to have any advantages. “We saw the same number of blood vessels in the blood-vessel-cell-alone group as in the co-cultured group, so we were a little disappointed,” Lavik says.

But two weeks later, the vascular networks that had developed from vessel cells alone had begun to die back—while those in the hybrid group were still generating new capillaries and circulating blood.

The ability to create self-sustaining networks of tiny blood vessels has vast implications for reconstructive medicine. Fringe surgical techniques such as replacing diseased heart muscle with tissue “patches” suddenly look a lot more feasible.

Lavik likes to dream about more distant possibilities, such as growing entire organs in the lab. “In order to make complex organs, you need to have a vascular supply,” she says. “I’m hoping this technique will contribute to making that supply.”  the end






The current Amazon conservation strategy, in which large sections of the rain forest are designated as “protected areas,” may not work, says environment school professor Lisa Curran in the March 23 issue of the journal Nature. Using a computer model called SimAmazonia, Curran and her colleagues show that conserving critical habitat outside the protected areas could help “avoid the collapse of regional rain forest ecosystems that is already occurring elsewhere in the tropics.”

Growing and maintaining human embryonic stem cells in the laboratory is a tricky business in which the cells often fail to thrive or differentiate into new cell types. In the April 11 Proceedings of the National Academy of Sciences, biologist Michael Snyder and his team reveal details of the “HESCO cocktail,” a simple mixture they developed that does the job. A patent application has been filed.

In the March 24 Cell, pharmacology professor Sven-Eric Jordt and his colleagues show that mustard, garlic, and the sushi condiment known as wasabi deliver their culinary kick through a specific pain receptor in sensory neurons called TRPA1. Because the receptor is also sensitive to irritants in tear gas, vehicle exhaust, and tobacco smoke, the researchers suggest that the discovery may lead to new pain medications and strategies to treat smoking- and environment-related illnesses.

Humans and chimpanzees are 99 percent identical genetically, and yet we’re very different in anatomy and behavior. The reason, argues Kevin White, an associate professor of genetics and ecology and evolutionary biology, and his colleagues in the March 9 issue of Nature, lies in key changes that took place over the last five million years in the way our genes are regulated—rather than in the genes themselves.


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