Tadpoles learn to see with new eyes transplanted on their tails
Written by Jessica Hamzelou
Blind tadpoles have learned to see again, using eyes implanted on their tails. With help from a migraine drug, these eyes were able to grow new connections to the tadpole’s nervous system. The same approach may work in humans, allowing the body to integrate bioengineered organs, say the team behind the work.
“If a human had an eye implanted on their back connected to their spinal cord, would the human be able to see out of that eye? My guess is probably yes,” says Michael Levin, at Tufts University in Medford, Massachusetts.
Levin is interested in how bioengineered organs might work within human bodies. Teams around the world have already created organs in the lab and implanted them in people, such as tracheas and bladders, and are now working on more complex organs, such as eyes and hearts.
But in order for these to work, the organs would have to be connected to the central nervous system, which controls the body and feeds information back to the brain.
To find out if the body might be able to adapt to a new eye, for instance, Levin’s team turned to frogs. Although they are very different to people, frogs share similarities with us at the molecular level, says Levin.
The team removed eyes from three-day old tadpoles, and attached a single one into each of the tails of other tadpoles of the same age. Some of these were then given a migraine drug on the site of their eye transplant, straight after the surgery. This drug, called Zolmitriptan, activates a class of serotonin receptors that seem to trigger electrical activity in cells – something that Levin’s team had previously discovered encourages the growth of neurons.
Only 5 per cent of the eyes attached to tadpoles that did not receive this drug grew new neurons, but 40 per cent of those that received the drug grew new neurons that reached their central nervous systems – an essential step for being able to send visual information to the brain for processing.
The team found that these tadpoles could see with their new eyes. They were able to learn the difference between red and blue areas, for instance, and to avoid coloured triangles as they moved on a screen beneath them.
The eyes did not even need to be connected to the animals’ brains for them to see – they only needed to be connected to the spinal cord. This is surprising, says Bernd Fritzsch at the University of Iowa.
This is good news for teams developing engineered organs like eyes and ears, says Fritzsch. “We have no idea how we would connect a retina to the brain, and if you wanted to replace an ear, you would have to cut out a big piece of the skull,” he says. “This work suggests that this might not be necessary – that you could put the organ on the neck, for example, and connect it to the spinal cord. It might look funny, but it could still work.”
But Fritsch says the team needs to find out whether the drug works the same way in people, and whether its effects extend beyond young animals to adults.
Journal reference: npj Regenerative Medicine, DOI: 10.1038/s41536-017-0012-5
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