Stimulating the brain using flashes of light might pave the way for a novel treatment for depression. Herbert Covington at Duke University in Durham, North Carolina, and colleagues have reversed the effects of stress-induced depression in mice using optogenetics – a technique in which light is used to stimulate in the brains of genetically modified mice. The team used herpes simplex virus to ferry the light-sensitive protein channel rhodopsin 2 (ChR2) into neurons in the medial prefrontal cortices of depressed mice: the mPFC is thought to orchestrate decision-making and social behaviour. Next they shone blue lasers on the mice mPFC in 40-millisecond bursts every three seconds for five minutes, stimulating the neurons in this area. After treatment the mice no longer showed signs of depression, with restored levels of social interaction and ability to experience pleasure, as measured by a 15 per cent increase in their preference for drinking sugar water over plain water. The team also discovered similar signatures of depression between the mice and humans. Examining the post-mortem brains of 20 people, Covington and colleagues found less messenger RNA for two genes present in the mPFCs of depressed people, indicating neurons fired less often there when they were alive. They found a similar result in depressed mice, suggesting that depression leaves similar footprints in mice and humans. The results are the first demonstration that optogenetics can “drive an antidepressant effect”, Covington says, but just as important is the improved understanding of the neurobiology of depression. While scientists knew that mPFC was important in depression, the causality was unclear. Now, there are signs that a change in the prefrontal cortex may influence a person’s mental state, says Covington. The next step will be to understand how mPFC interacts with other brain regions to create or respond to depression, he adds. That researchers are using an optogenetic method to study depression “is fantastic progress”, says Helen Mayberg, a neuroscientist and clinical psychiatrist at Emory University in Atlanta, Georgia. “Nobody was looking at this region [in animal studies] despite constant begging for ten years,” she says.
Source: New Scientist
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