A group of American scientists have just made a great contribution to our understanding of bioengineered eyes. One new study out of Tufts University shows that with the proper medication it is possible for implanted eyeballs to grow new neural networks in blind tadpoles. While researchers can't say the same would work for human beings, the results from this tadpole test certainly make it a more viable possibility.
Researchers involved in this study first removed the eyes from a group of three-day old tadpoles. They then attached bioengineered eyes to each of these tadpoles' tails. Doctors only gave about half of the tadpoles in this study the drug Zolmitriptan, which is generally used for treating migraine headaches.
Of the tadpoles that only received an eye injection, about 5 percent were able to regenerate neurons in their new eyes. However, 40 percent of the tadpoles that received regular doses of Zolmitriptan grew enough neurons to actually see out of their tails.
The main reason Zolmitriptan works so well is because it stimulates the body's serotonin receptors and sparks electrical activity in various cells. Numerous other tests at Tufts and other universities have shown a positive correlation between the growth of neurons and the use of drugs like Zolmitriptan.
To double-check their research, the scientists put tadpoles to the test in different colored areas. They found that tadpoles were able to avoid various colored shapes as they moved on a screen below them.
Perhaps the most amazing part of this study is the fact that the tadpoles didn't need their eyes to be connected to their brain to see clearly. As long as the bioengineered eye was connected to the spinal cord, it was able to grow enough neurons to function properly.
Professor Michael Levin, the current head of the Allen Discovery Center at Tufts, was the lead researcher in this tadpole project. When asked what this study meant for humans, Levin said that it's now possible to imagine a world where human beings could see out of implanted eyes on their backs.
Although this is one of the first successful tests of a bioengineered eye, many other scientific teams around the world have created numerous successful organs. A few simplistic organs that have been successfully implanted into human patients include bladders and tracheas. Most research groups involved in this kind of study are now interested in working on complex organs like hearts and eyes.
Professor Bernd Fritzsch, who researches biological regeneration at University of Iowa, was pleasantly surprised with the results from the tadpole study. Since this research suggests that it's not necessary to connect the retina directly to the brain, Fritzsch believes scientists of tomorrow could design eyes or ears and attach them to our necks or backs. Although it might look silly to see an ear or eye on the back of a person's neck, Fritzsch said this could potentially work.
Levin's full study was published in the journal NPJ Regenerative Medicine under the title "Serotonergic stimulation induces nerve growth and promotes visual learning via posterior eye grafts in a vertebrate model of induced sensory plasticity."