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Archive - Dec 12, 2012

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Depression-Like States Can Be Switched On and Off in Mice

A specific pattern of neuronal firing in a brain reward circuit instantly rendered mice vulnerable to depression-like behavior induced by acute severe stress, a study supported by the National Institutes of Health has found. When researchers used a high-tech method to mimic the pattern, previously resilient mice instantly succumbed to a depression-like syndrome of social withdrawal and reduced pleasure-seeking – they avoided other animals and lost their sweet tooth. When the firing pattern was inhibited in vulnerable mice, they instantly became resilient. "For the first time, we have shown that split-second control of specific brain circuitry can switch depression-related behavior on and off with flashes of an LED light," explained Ming-Hu Han, Ph.D., of the Mount Sinai School of Medicine, New York City, a grantee of NIH's National Institute of Mental Health (NIMH). "These results add to mounting clues about the mechanism of fast-acting antidepressant responses." Dr. Han, Eric Nestler, M.D., Ph.D., of Mount Sinai, and colleagues, reported the results of their study online on December 12, 2012, in Nature. In a companion article, NIMH grantees Kay Tye, Ph.D., of the Massachusetts Institute of Technology, Cambridge, Massacusetts, and Karl Deisseroth, M.D., Ph.D., of Stanford University, Stanford, California, used the same cutting-edge technique to control mouse brain activity in real time. Their study reveals that the same reward circuit neuronal activity pattern had the opposite effect when the depression-like behavior was induced by daily presentations of chronic, unpredictable mild physical stressors, instead of by shorter-term exposure to severe social stress. Prior to the new studies, Dr.

Algal Ancestor Is Key to How Deadly Pathogens Proliferate

Long ago, when life on Earth was in its infancy, a group of small single-celled algae propelled themselves through the vast prehistoric ocean by beating whip-like tails called flagella. It's a relatively unremarkable story, except that now, more than 800 million years later, these organisms have evolved into parasites that threaten human health, and their algal past in the ocean may be the key to stopping them. The organisms are called apicomplexa, but people know them better as the parasites that cause malaria and toxoplasmosis, serious diseases that infect millions of people every year, particularly in the developing world. Now, researchers at the University of Georgia (UGA) have discovered how an important structure inside these parasitic cells, which evolved from the algal ancestor millions of years ago, allows the cells to replicate and spread inside their hosts. The research may soon lead to new therapies to halt these deadly pathogens before they cause disease. In order to survive, the parasitic apicomplexa must invade an animal or human and force its way into the cells of its host. Once inside the host cell, the parasite begins to replicate into numerous daughter cells that in turn create additional copies, spreading the infection throughout the body. In their study, published December 11, 2012 in PLoS Biology, the researchers demonstrate that, during the process of replication, the parasite cell loads genetic material into its daughter cells via a strand of fiber that connects the two. By altering the genes for the components of the fiber in the laboratory, the researchers discovered that they could prevent parasite replication, making the parasite essentially harmless.