BETHESDA, Md., June 23, 2011 Say what you will about bird brains, but our feathered friends sure have us -- and all the other animals on the planet -- beat in the vision department, and that has a bit to do with how their brains develop.
Consider the in-flight feats of birds of prey: They must spot their dinner from long distances and dive-bomb those moving targets at lightning speed. And then there are the owls, which operate nimbly on even the darkest nights to secure supper in swift swoops. Some birds have ultraviolet sensitivity; others have infrared sensitivity. To boot, some birds can even see the Earth's magnetic field.
Much of the credit for avian visual acuity goes to the extraordinary retina, which grows out of the brain during development, making it an official component of the central nervous system. Indeed, the avian retina is far more complex in structure and composition than the human retina, and it contains many more photoreceptors -- rod- and cone-shaped cells that detect light and color, respectively.
While researchers over the years have come to better understand much about the avian retina, many nagging questions remain. For Thorsten Burmester's research team at the University of Hamburg, the question was this: How does such a productive retina sustain itself when the avian eye has very few capillaries to deliver oxygen to it? After all, it has to "breathe," so to speak.
"The visual process in the vertebrate eye requires high amounts of metabolic energy and thus oxygen," Burmester's group writes in this week's Journal of Biological Chemistry. "Oxygen supply of the avian retina is a challenging task because birds have large eyes, thick retinas and high metabolic rates, but neither deep retinal nor superficial capillaries."
To answer the question, Burmester's team took a closer look at a protein that they discovered exists in large quantities in photoreceptor cells of the avian eye -- and o
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American Society for Biochemistry and Molecular Biology