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Researchers in the States have been exposing mice to low oxygen levels, such as the like you would be submitted to at high altitude to increase the resistance of optical nerve cells to damage. The stress of an intermittent low-oxygen environment has facilitated a protective response called tolerance that makes nerve cells less susceptible to harm. The study is the first to show that induced preconditioning tolerance can help protect against a neuro-degenerative disease.
Stress is generally labelled as a negative phenomenon, neurological surgeons and ophthalmologists have previously shown that low level stress such as exercise and also environments with low oxygen levels, can precondition cells and that makes them more resistant to diseases and injury.
It was previously thought that tolerance in our central nervous system could only last a few days but a preconditioning protocol was developed last year that is extending the effects from days to months. The US study had been exposing mice to hypoxia (low concentration of oxygen) several times over a period of a fortnight and the scientists triggered an extended period of tolerance. At the end of the preconditioning, the brain was reported to have been protected from damage via stroke for at least 8 weeks.
With the tolerance period extended, it led to the scientists debating whether a prolonged period of injury resistance could also protect against the slow, progressive loss of neurons that characterizes neuro-degenerative diseases.
They looked at an animal model of glaucoma. The only treatments for glaucoma are drugs that reduce pressure in the eye; as yet there are no therapies to protect the retina and optical nerves from harm.
Glaucoma is categorised as a neuro-degenerative disease based on how progressively it kills retinal ganglion cells over a slow period of time. The bodies of the cells are found in the eyes retina and their branches come together in bundles and form the optic nerves. It is not known whether damage begins in the bodies or axons of the cells, but as more retinal ganglion cells die, peripheral vision loss is experienced by patients which eventually leads to blindness.
The new study, induced glaucoma in mice by tying off vessels that allow fluid to drain from the eye. This caused increased eye pressure so an assessment could be carried out as to how many cell bodies and axons of retinal ganglion cells were still intact after three or ten weeks.
It was reported that normal mice lost an average of 30 percent of their retinal ganglion cell bodies after 10 weeks of glaucoma. However mice that received the preconditioning before glaucoma-inducing surgery lost only 3 percent of retinal ganglion cell bodies.
There are current investigations into which genes are activated or repressed by preconditioning. It is hoped that that the change in gene activity can be identified that makes cells more resistant to damage.
Identifying these specific survival genes will assist in the development of drugs that can activate them.