Scientists Restore Partial Vision to Blind Mice


The optic nerve, which is located behind the eye, is an attachment that carries visual messages from the retina to the brain. Until now, it was assumed that these particular nerve cells could not be regenerated. But an increase in activity of a protein called mTOR (mechanistic target of rapamycin) seems to assist in nerve cell regeneration. Among other things, mTOR regulates cell growth, cell proliferation, cell motility, and cell survival. The protein mTOR stimulates the axons along the optic nerve to regenerate, although not yet quite enough to restore vision. 

The next step was that the scientists genetically bred mice that produce a whole lot of mTOR in their retinal nerve cells. Then they crushed the optic nerve and blinded the mice in one eye. After that, the mice hung out in their cages, watching projections of moving black lines. Three weeks later, researchers discovered that the axons of the optic nerve in the damaged eye had partially regrown.

So they took it a step further. The researchers decided to sew the good eyes shut, forcing the mice to watch the projections with their damaged eyes. According to the author's report in Nature Neuroscience, the positive result was 500 times better than the previous positive result, with some of the regenerated axons extending all the way to the brain. The axons even seemed to "know" where to go, automatically reconnecting with their previous target sites. On the down side, not all of the axons in all of the mice regenerated.

After the experiment, the mice were subjected to a succession of vision tests. It turned out that, although they could still track moving objects and see things overhead, they lacked depth perception. What's interesting is that creatures who are blind in one eye are known to lack depth perception. You have to have vision in both eyes to have depth perception. The optic nerve may have regenerated physically, without necessarily restoring sight to the mouse. Are we quite sure these mice could see out of the bad eye?

In any case, Andrew Huberman, who co-authored the study, hopes to perfect this discovery in order to invent new treatments for vision impairments in humans. Common eye problems in humans include eye injury, cataracts, glaucoma, and retinitis pigmentosa. Huberman sees a future in which mTOR can be used for this purpose.

Yet, mTOR is not such a good thing, necessarily. For instance, a decrease in mTOR activity is associated with an increased life span. Also, mTOR seems to be a contributor to the progression of Alzheimer's disease. It is even linked with certain types of cancer. After all, cancer is basically defined as rapid cell growth. In fact, mTOR inhibitors are used therapeutically, like rapamycin, which is already being administered to ward off organ transplant rejection, especially in the kidneys. Do we really need all this mTOR?

That's the other side of the argument. 

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