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Old 08-31-2009, 10:21 AM   #1
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Default Birds' Light Meter Discovered

Birds' Light Meter Discovered

By Cassandra Willyard
ScienceNOW Daily News
7 August 2009

Birds' Light Meter Discovered -- Willyard 2009 (807): 3 -- ScienceNOW
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But how do birds sense these longer days? Experiments in the 1930s showed that the key lies not in a bird's eye, as one might expect, but in the hypothalamus, a region deep in the brain. To demonstrate this, a French scientist inserted thin glass rods into the hypothalamus of blinded ducks in order to artificially illuminate only that part of the brain. Exposing the ducks' brains to springlike day lengths prompted testicular growth. Winter day lengths had no effect.

In many ways, it makes sense that a seasonal sensor would reside deep in the brain, Foster says. Bird's skulls are so thin and their brains are so small that light can penetrate to cells in the interior. Furthermore, the sensor is "close to all those bits in the hypothalamus that are regulating the reproductive system," he says.

Although these early experiments hinted at the approximate location of the light sensors, for decades no one could pinpoint exactly what they were. Fresh clues came in 1997 when Foster's team discovered a new light-sensitive protein in the eyes of salmon and named it vertebrate ancient opsin (VA opsin). Because the protein also appeared in fish brains, the researchers "got terribly excited," Foster says. "We thought, 'Great! This is going to be the brain photoreceptor of birds and reptiles and amphibians and fish.'" But over the next decade, researchers failed to find any evidence of VA opsin in other vertebrates. Foster and colleagues didn't give up, however, and their persistence has paid off.
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avian news, avian research, behaviors, bird, bird behavior, birds, discovered, light, light sensors, light-sensitive protein, meter, photoreceptor

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