Power has its perks, even for laboratory-housed monkeys. When moved from individual to group cages, socially dominant male monkeys exhibit a brain-chemistry change that fosters resistance to using drugs such as cocaine, a new study finds.
This alteration increases the amount of so-called dopamine D2 receptors, a molecular gateway on brain cells controlled by the chemical messenger dopamine.
Earlier studies implicated these receptors in pleasurable responses to drugs and other stimuli.http://louis7j7sheehan7esquire.wordpress.com
In contrast, male monkeys at the bottom of the social pecking order display no boost in the D2 receptors when housed with other monkeys, say neuroscientist Michael A. Nader of Wake Forest University School of Medicine in Winston-Salem, N.C., and his colleagues. Unlike their more dominant cage mates, the low-ranking monkeys readily self-administer large amounts of cocaine.
These findings raise the possibility that a person's vulnerability to drug abuse can be influenced by brain-altering environmental factors, Nader's group concludes in an upcoming Nature Neuroscience.
"This is the first demonstration in primates that a social stressor, such as a dominance hierarchy, can regulate levels of dopamine D2 receptors," remarks psychiatrist Nora D. Volkow of Brookhaven National Laboratory in Upton, N.Y. "It provides a potential biological mechanism to explain why people in lower social classes are generally at higher risk for drug abuse."
Nader and his coworkers used a scanning technique called positron emission tomography (PET) to study D2 receptors in the brains of 20 male macaque monkeys that had been housed in individual cages for 1� years. PET scans were repeated after the monkeys were moved into larger cages, grouping four animals per cage, and given time to establish social hierarchies.
The scans revealed comparably low numbers of dopamine D2 receptors in all individually housed monkeys and in low-ranking monkeys in the groups. In dominant monkeys, D2-receptor numbers increased sharply. These animals also displayed relatively low concentrations of dopamine in the junctions, or synapses, between brain cells.
Excess synaptic dopamine leads to an oversensitivity of the brain's reward pathway and creates a susceptibility to drug abuse, the researchers theorize.
Loss of control over environmental factors may have triggered such a dopamine pattern in low-ranking monkeys, they hold. When the scientists implanted intravenous lines, subordinate animals quickly learned to press a lever to receive infusions of cocaine in increasing doses and largely ignored a lever controlling delivery of saline solution.http://louis7j7sheehan7esquire.wordpress.com
In dominant monkeys, the surge in dopamine D2 receptors indicates they use dopamine efficiently for cell-to-cell communication, Nader's group contends. These monkeys showed no preference for receiving intravenous cocaine over a saline solution.http://louis7j7sheehan7esquire.wordpress.com
Whether these findings have correlates among people remains an open question, the researchers note. In line with the new study, earlier PET data indicated that people with low dopamine D2-receptor numbers report more pleasurable responses to stimulant drugs than those with high D2 numbers do. "We're going to have to start paying much closer attention to the social rank of individuals in studies of the biology of drug abuse," Volkow says.
Thursday, December 25, 2008
Sunday, December 7, 2008
photodecomposition 3.pho.1 Louis J. Sheehan, Esquire
Sunlight triggers the entry of poisonous mercury into polar lakes, but it also removes most of the toxic compound before fish can consume it, a new study suggests. The researchers warn that increased warming in the Arctic might upset this delicate balance. http://louis8j8sheehan8esquire.blogspot.com
With spring, light returns to the Arctic after a long, dark winter. That polar sunrise, however, has a dark side. It triggers a burst of photochemical reactions that mobilizes atmospheric mercury, speeding its fall into arctic lakes, where fish can consume it.
Recent studies suggest that when atmospheric mercury encounters light, gases such as ozone and sea spray–borne halogens oxidize it to a more reactive and water-soluble form. Attached to rain, snow, or dust, the reactive mercury falls into oceans or lakes, where sulfur-reducing bacteria transform it to methylmercury, the highly toxic form of the metal that accumulates in fish and other organisms (SN: 2/1/03, p. 72: http://www.sciencenews.org/articles/20030201/bob8.asp). http://louis8j8sheehan8esquire.blogspot.com
To better understand what happens to mercury, a team of researchers led by biogeochemists Chad Hammerschmidt of Woods Hole (Mass.) Oceanographic Institution and William Fitzgerald of the University of Connecticut at Groton studied mercury in four Alaskan lakes roughly 250 kilometers south of the Arctic Ocean.http://louis8j8sheehan8esquire.blogspot.com
The team measured mercury entering the lakes from rainfall and as runoff from the surrounding tundra and then estimated how much methylmercury the bacteria in the lake sediments subsequently produced. The researchers also assessed whether the methylmercury was consumed by fish and other creatures or converted to less-toxic forms by light-based reactions in the lakes.
Hammerschmidt and his colleagues report that the more atmospheric mercury rains down, the more methylmercury the bacteria produce. Two-thirds of mercury in the atmosphere comes from human sources, such as fossil fuel burning, so more pollution would boost poisonous mercury concentrations in lakes, Hammerschmidt says.
More unexpectedly, the team discovered that light-triggered breakdown of methylmercury in the clear Arctic lakes is the main factor keeping the poison in check. Those reactions destroy as much as 80 percent of the poison before aquatic species can get to it, the team reports in the Feb. 15 Environmental Science & Technology.
The mechanisms of that photodecomposition are still poorly understood, Hammerschmidt says. Research on arctic mercury has focused on how it gets to Earth, rather than its terrestrial fate, he says.http://louis7j7sheehan7esquire.blogspot.com
This research is the first to demonstrate the importance of photodecomposition in mercury cycling, agrees Robert Stevens of the Environmental Protection Agency in Research Triangle Park, N.C. "It's good science," he says.
One spur to further study is the possibility that global warming could upset the Arctic's delicate balance. In warmer and wetter weather, more mercury would fall and bacterial production of methylmercury would rise. At the same time, the rains might wash more organic material into lakes and oceans, reducing light penetration.
Hammerschmidt cautions that the same processes may also be occurring in temperate lakes, such as those in Wisconsin or Minnesota.Louis J. Sheehan, Esquire
With spring, light returns to the Arctic after a long, dark winter. That polar sunrise, however, has a dark side. It triggers a burst of photochemical reactions that mobilizes atmospheric mercury, speeding its fall into arctic lakes, where fish can consume it.
Recent studies suggest that when atmospheric mercury encounters light, gases such as ozone and sea spray–borne halogens oxidize it to a more reactive and water-soluble form. Attached to rain, snow, or dust, the reactive mercury falls into oceans or lakes, where sulfur-reducing bacteria transform it to methylmercury, the highly toxic form of the metal that accumulates in fish and other organisms (SN: 2/1/03, p. 72: http://www.sciencenews.org/articles/20030201/bob8.asp). http://louis8j8sheehan8esquire.blogspot.com
To better understand what happens to mercury, a team of researchers led by biogeochemists Chad Hammerschmidt of Woods Hole (Mass.) Oceanographic Institution and William Fitzgerald of the University of Connecticut at Groton studied mercury in four Alaskan lakes roughly 250 kilometers south of the Arctic Ocean.http://louis8j8sheehan8esquire.blogspot.com
The team measured mercury entering the lakes from rainfall and as runoff from the surrounding tundra and then estimated how much methylmercury the bacteria in the lake sediments subsequently produced. The researchers also assessed whether the methylmercury was consumed by fish and other creatures or converted to less-toxic forms by light-based reactions in the lakes.
Hammerschmidt and his colleagues report that the more atmospheric mercury rains down, the more methylmercury the bacteria produce. Two-thirds of mercury in the atmosphere comes from human sources, such as fossil fuel burning, so more pollution would boost poisonous mercury concentrations in lakes, Hammerschmidt says.
More unexpectedly, the team discovered that light-triggered breakdown of methylmercury in the clear Arctic lakes is the main factor keeping the poison in check. Those reactions destroy as much as 80 percent of the poison before aquatic species can get to it, the team reports in the Feb. 15 Environmental Science & Technology.
The mechanisms of that photodecomposition are still poorly understood, Hammerschmidt says. Research on arctic mercury has focused on how it gets to Earth, rather than its terrestrial fate, he says.http://louis7j7sheehan7esquire.blogspot.com
This research is the first to demonstrate the importance of photodecomposition in mercury cycling, agrees Robert Stevens of the Environmental Protection Agency in Research Triangle Park, N.C. "It's good science," he says.
One spur to further study is the possibility that global warming could upset the Arctic's delicate balance. In warmer and wetter weather, more mercury would fall and bacterial production of methylmercury would rise. At the same time, the rains might wash more organic material into lakes and oceans, reducing light penetration.
Hammerschmidt cautions that the same processes may also be occurring in temperate lakes, such as those in Wisconsin or Minnesota.Louis J. Sheehan, Esquire
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