It's hard to say what's crazier: the fact that Tufts University researchers spent a year cutting out the tiny eyeballs of tadpole embryos and sticking them back on to the tadpoles' tails, or: the fact that, when they hatched, a few of the tadpoles COULD ACTUALLY SEE OUT OF THE EYES ON THEIR TAILS.
As you know, this is not the way vision is supposed to work--your eyeballs are supposed to be connected to a big fat nerve that carries incoming signals back to your brain, which combines the information from both your eyes into a 3D picture of the world in front of you. Without that direct link to the brain, your eyeballs are useless.
At least, that's the way scientists have thought about it for the last several centuries. But over the past few decades, experiments in animals and humans have repeatedly shown that the central nervous system--including the brain and spinal cord--is a lot more flexible and adaptable than people used to think it was. If one part of the brain gets damaged, for instance, the information that used to flow to the damaged sector is often re-routed, and another part of the brain takes on the job of processing it.
So these newer findings got the Tufts University researchers wondering: could the optic nerve really be the only route for incoming visual signals? And could a different part of the nervous system, like the nerves further down the spinal cord, process those signals on their own, without help from the brain?
Tadpoles, they realized, would be a good way to test this question: they would perform surgery at a time when the tadpoles were still developing, so that the transplanted eyes would have time to put down nerve roots that could potentially hook up to the rest of the tadpoles' nervous systems.
The surgeries were painstaking, but the researchers were able to successfully graft eyeballs onto the tails of over 200 tadpole embryos:
When the altered tadpoles hatched, the researchers went to work testing their subjects' vision. Here's the Journal of Experimental Biology's description of the experiment:
While the blind tadpoles never developed a preference for one side of the dish or the other, seven of the tadpoles with transplanted eyes learned to stay in the blue light, demonstrating that they could see through their grafted eyes.
The question was, why only seven?
The answer turned out to have something to do with how the donor eyes sprouted nerves after the transplants. Since they'd labeled the donor eyes with red fluorescent protein, the researchers were able to image the tadpoles and compare the growth of their nerves. In half the subjects, the nerves hadn't grown at all, and in about a quarter of the others, the nerves had grown, but they'd ended up in the tadpoles' stomachs:
But in the other quarter of the subjects--31 tadpoles in total--the nerves extended all the way to the animals' spinal cords; six of the seven seeing tadpoles belonged to this group:
The researchers' findings seem to indicate that the neurons in the spinal cord are capable of doing at least some of the tasks as the brain. If that's true, scientists could someday exploit the spinal cord's smarts for a number of medical treatments, like restoring movement to paralyzed limbs.
The only thing we regenerate seems to be liver tissue, so could with a blastocyst from our own stem cells regenerate other organs in place of part of our liver?
Soon, Argus will live.
Good job PopSci! This article points out a very troubling issue for Darwinists. The plasticity of these tadpoles is hard to account for in evolutionary terms.
How many things got rewarded for reproducing the ability to have stuff removed from the body and put somewhere else?
Science thrives when ideas are challenged. And Darwin doesn't see enough challenges by most of the 'scientists'.
"Darwinists". STFU, bagpipes. There's a reason why the theory of evolution is as widely regarded as FACT by the scientific community; because it has been challenged by science over the past 150 years and is continuously supported by more findings. Get over it. Facts are facts whether you like them or not.
Um yeah no Bagpipes it doesn't point out a troubling issue, it just gives us insight into the nature of the nervous system that we were unaware of. This would even potentially lend support to the idea that evolution happens as a means of adaptation to unexpected changes in their environment as the cutting out of their eyes and the addition of one on the tail is an environmental hazard. As seven of the tadpoles could potentially survive while the rest of the blind ones would die that would make those seven with some semblance of sight just a little more likely to survive and reproduce. The ability for the nervous system to adapt to problems in initial development are very advantageous to the potential of the animal in question to survive.
Nice straw man attack, Bagpipes.
If you've just proved one thing to everyone here, it's that the country can't afford the Sequester cuts to education...
Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.
- Albert Einstein
Bagpipes is just full of hot air.
I think calling it a "working eye" is a bit of a stretch. The animal could sense light and dark with the transplanted eye, but that's not the same as actually seeing with the eye. Still and interesting find.
Every scientist has a little Dr. Frankenstein in him/her.
David, even an eye that just senses light is a functioning eye. Rudimentary, but still functioning. Complex eyes certainly evolved from these simple eyes. An eye that senses a sudden change in light may signal the organism to evade. A concave depression with the light receptors at the base would go further to allow the organism to discern from which direction the light changed. You can go further to end at the complex eyes we possess.
Geez, I sound like such a "Darwinist"...