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Thursday, January 22, 2009

Ancient African Exodus Mostly Involved Men, Geneticists Find

Newswise — Modern humans left Africa over 60,000 years ago in a migration that many believe was responsible for nearly all of the human population that exist outside Africa today.

Now, researchers have revealed that men and women weren’t equal partners in that exodus. By tracing variations in the X chromosome and in the non-sex chromosomes, the researchers found evidence that men probably outnumbered women in that migration. The scientists expect that their method of comparing X chromosomes with the other non-gender specific chromosomes will be a powerful tool for future historical and anthropological studies, since it can illuminate differences in female and male populations that were inaccessible to previous methods.

While the researchers cannot say for sure why more men than women participated in the dispersion from Africa—or how natural selection might also contribute to these genetic patterns—the study’s lead author, Alon Keinan, notes that these findings are “in line with what anthropologists have taught us about hunter-gatherer populations, in which short distance migration is primarily by women and long distance migration primarily by men.”

These findings are published in Nature Genetics.

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Wednesday, January 21, 2009

Scientists Discover an Ancient Odor-Detecting Mechanism in Insects

Newly discovered receptors in the nose of a common insect unearths one of the most ancient mechanisms that organisms have evolved to smell. Ionotropic glutamate receptors, proteins that reside deep in the brain at the synapses, grab glutamate molecules and quickly relay messages from one nerve cell to the next, helping animals learn, move and remember. But insects do not relegate these receptors to the depths of the brain. They also put them to use elsewhere: in the nose.

"On the surface it's a completely absurd idea," says Leslie B. Vosshall, head of the Laboratory of Neurogenetics and Behavior at Rockafeller University. "We know what these proteins do; they sit at the synapse and mediate fast neuronal communication. So the idea that the fly has massively expanded the number of these receptors and positioned them to interact with small molecules in the air seems very strange. But if you think about it, it makes sense. The process is the same, but rather than grabbing small molecules at the synapse, they're grabbing small molecules from the air."

The project began two years ago, when Vosshall and Richard Benton, then a postdoc in her lab, noticed a group of six ionotropic glutamate receptor genes while sifting through the fly genome. Although this group was recognized 10 years ago, ever since the genome was sequenced, the genes did not have a known function, in part because it was assumed they must be similar to any other ionotropic glutamate receptor deep in the fly brain. But to Vosshall and Benton, who is now at the Center for Integrative Genomics in Lausanne, Switzerland, that didn't matter.

Vosshall and her team wondered whether these receptors could in fact represent the "missing" receptors thought to exist in the fly's "nose" -- its two antennae. Each antenna is divided into three types of smell neurons. Scientists have characterized the receptors that detect odors in two of these types but those receptors were mysteriously absent in the third, a swath of territory known as the coeloconic sensilla. "It has been shown that cells in the coeloconic sensilla detect odors," Vosshall says. "It's just that we didn't know how they did it."

The team showed that these receptors, which the Vosshall lab named ionotropic receptors, do in fact explain how cells in coeloconic sensilla detect odors. First, they showed that they are expressed in complex combinatorial patterns at the sensory end of olfactory neurons where they have access to and can scan the outside world for odors. They then showed that when these receptors are expressed in the cells in the coeloconic sensilla, the cells respond to odors. Finally, the researchers showed that when they plucked a receptor -- say one that detects an odor that resembles a mix of grass and honey -- out of its native cell and genetically embedded it in a different cell, the new cell would now detect that odor.

Although it is still unclear why insects have developed two sets of chemosensory receptors -- olfactory receptors and ionotropic receptors -- the work raises questions regarding their evolutionary origin. Ten years ago, researchers at New York University revealed that plants, which detect soil nutrients and chemicals in the air, also express glutamate receptors, suggesting that the ancestral origin of glutamate receptors may have been to detect small molecules in the air, rather than small molecules in the brain.

"In a way, these receptors were very well hidden because everyone assumed that they were extra glutamate receptors that were unlikely to be of interest," explains Vosshall. "All we did to find them was searched for a gene family of unknown function -- and left our preconceived notions aside."

This work was funded in part by grants from the Foundation for the National Institutes of Health through the Grand Challenges in Global Health Initiative and the National Institutes of Health.

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Vets and Depression: Return from War to Fight New Battle

Newswise — When Lamont Christian returned from war, he often felt angry, afraid and unworthy. Years later, Christian found himself living in a homeless shelter, a sign that time had not healed his emotional wounds.

He went to the VA Ann Arbor Healthcare System for help, and there, he learned the root of his problems: he was suffering from depression, post-traumatic stress disorder and anger management problems. Now, he wants others to learn from his experience.

"If I had a message to give to veterans who are coming out of the military now or even veterans who have been out for a long period of time, it's that nothing is going to happen in your life unless you go and get the help you need," he says.

Christian is a veteran of Vietnam, but his experience holds true for soldiers returning from current battlegrounds as well.

Nearly a third of veterans who are treated at Veterans Affairs health care centers have significant depressive symptoms, and about 13 percent have clinically diagnosed depression, says Marcia Valenstein, M.D., clinical psychiatrist with the VA Ann Arbor Healthcare System and associate professor of psychiatry with the University of Michigan Health System.

Depression is a "very potent" risk factor for suicide among people receiving treatment for depression at the VA, she notes, with a suicide rate that is three times higher than that of the overall VA patient population.

Such high rates led Valenstein and her colleagues to study the best time to provide intensive interventions to veterans with depression to prevent suicide. In a study just published by the Journal of Affective Disorders, the researchers found that veterans with depression were at highest risk for suicide in the 12 weeks after they were hospitalized for psychiatric conditions.

"This finding highlights the need for very close follow-up for patients who are discharged from our inpatient services because this is a particularly vulnerable time for them," says Valenstein, a core investigator with the Serious Mental Illness Treatment Research and Evaluation Center at the VA Ann Arbor Healthcare System.

Current government recommendations have focused on providing intensive follow up for patients following all new antidepressant starts. More attention needs to be paid to the highest-risk periods that follow psychiatric hospitalization, Valenstein says. "Health systems with limited resources should focus their efforts on this time period to have the greatest impact on suicide prevention."

The Department of Veterans Affairs has made mental health issues a priority, Valenstein notes. VA health centers have received more than $300 million for expansion of suicide prevention and other mental health services from the Veterans Health Administration.

Note: The views expressed in the study are those of the authors and do not necessarily represent the views of the Department of Veterans Affairs.

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