Mice get their vision back with regrown neurons

If the nursery rhyme “Three Blind Mice” taught us anything (and let’s be clear here, it absolutely wasn’t supposed to), it’s that we don’t really know what to do with mice with visual impairment. Scientists at Stanford University have changed all that with a landmark study, in which they managed to restore some of the vision in mice using regrown neurons.

This is a big deal. We’ve known for a while that chickens, frogs and fish can regrow their brain cells, but this is the first time that it has been proven in mammals. This could, potentially, open the door to treatments for human diseases that have previously proved difficult, such as glaucoma and spinal-cord injuries.

“Reconnecting neurons in the visual system is one of the biggest challenges to developing regenerative therapies for blinding eye diseases like glaucoma,” said Paul A Sieving, director of the National Eye Institute (NEI). “This research shows that mammals have a greater capacity for central nervous system regeneration than previously known.”

Using a combination of chemically induced neural stimulation and high-contrast visual stimulation, researchers were able to restore a small number of the mice’s retinal ganglion cells – less than 5%, but enough to show potential. Test mice – genetically engineered to produce higher levels of a protein called mTOR in their retinal nerve cells – had their optic nerve crushed behind one eyeball. Over a period of three weeks, the mice were made to watch projections of moving black lines.

READ NEXT: The technology helping blind people to see

After this time, the researchers found that the axons of the crushed optic nerve had partially regrown, reaching as far as the optic chiasm – a distance of around six millimetres. The scientists then managed to improve results further by forcing the mice to use their damaged eye, by suturing the good eye shut. Results were even more pronounced.

“We saw the most remarkable growth when we closed the good eye, forcing the mice to look through the injured eye,” said Dr Andrew D Huberman, associate professor at Stanford University’s neurobiology department. In this instance, the axons would grow 12 millimetres – around 500 times faster than central nervous system axons without treatment.

Better still, the axons connected to the right target site within the brain, suggesting some kind of “memory” of where they belong. “The two types of retinal ganglion cells that we looked at – α-cells and melanopsin cells – seemed fully capable of navigating back to correct locations in the brain, plugging in and forming synapses,” explains Huberman. “And just as interesting, they didn’t go to the wrong places.”

The hope is that this promising start can one day be used to examine the treatment of humans. Huberman believes that therapies building on these results could include filters for VR games and TV programmes, or simply glasses that deliver regeneration-inducing visual stimulation. However, the researchers are aware that optic nerve crush isn’t the perfect analogue for blinding diseases and injuries, so in the short term, the next step is to look at the effect on a mouse glaucoma model, and try to nail down the exact qualities of visual stimuli that drive retinal regeneration.

Images: Al Steel and Elena Gurzhiy used under Creative Commons