Researchers are working on creating regeneration in mammals where it does not normally happen: "Researchers have long tried to get the optic nerve to regenerate when injured, with some success, but no one has been able to demonstrate recovery of vision. A team [now] reports a three-pronged intervention that not only got optic nerve fibers to grow the full length of the visual pathway (from retina to the visual areas of the brain), but also restored some basic elements of vision in live mice. ... [the mice were able to] regain some depth perception, the ability to detect overall movement of the visual field, and perceive light. ... Previous studies [have] demonstrated that optic nerve fibers can regenerate some distance through the optic nerve, but this is the first study to show that these fibers can be made to grow long enough to go from eye to brain, that they are wrapped in the conducting 'insulation' known as myelin, that they can navigate to the proper visual centers in the brain, and that they make connections (synapses) with other neurons, allowing visual circuits to re-form. ... [Researchers] combined three methods of activating the growth state of neurons in the retina, known as retinal ganglion cells: stimulating a growth-promoting compound called oncomodulin, [elevating] levels of cyclic adenosine monophosphate (cAMP) and deleting the gene that encodes the enzyme PTEN. ... these interventions have a synergistic effect on growth of optic nerve fibers. ... The eye turns out to be a feasible place to do gene therapy. The viruses used to introduce various genes into nerve cells mostly remain in the eye. Retinal ganglion cells are easily targetable."
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