The ability to grow brain and spinal cord nerve cells is present at birth- and starts to disappear just like that as we age. So, when we incur an injury to the spine or the brain- the axons (as discussed earlier) can’t regenerate. It is thought that since these areas are replete with nerves and nerve fibers, they send signals to stop new connections from forming. By stopping new pathways from forming, our brain can’t be confused with by incorrect signals that could result from the new pathways.
When a finger is, unfortunately, severed, it can be reattached surgically. Most times, the nerve fibers grow back and develop valid connections. That’s why the finger can be used properly, with time. That does not happen with spinal cord injuries. In this region, compounds are produced, axon regeneration inhibitors (these chemicals provide the signals described above), that stop such regeneration.
A team of researchers at Harvard University, UC San Diego and UC Irvine are trying to change just that, by switching on the pathway that turns off our ability to regenerate the nerve cells. The two lead researchers, Osward Steward and Zhigang He, have been studying nerve plasticity- the ability of nerves to grow or make new connections to bypass damaged areas, for some time. Their research found that PTEN (phosphatase tensin homolog), a tumor suppression gene, seems to be critical in the diminuation of neural regrowth. By removing the PTEN gene, mTOR concentrations increased; together these seemed to be the critical controllers of corticospinal neuron regeneration. On young mice, they found significant spinal cord nerve regeneration. The results of this study will be published soon in Nature Neuroscience. .
This research was predicated upon the removal of the gene. It will be critical to find a means to turn off the pathway, for it to have utility for humans, as opposed to removing genes. It is also unclear if this process would work in adult mice; the research used young mice, which may not have lost all their ability to regrow nerve cells. It should be noted that this new result is not going to find its way to human trials soon.