A team of scientists from the University of California San Diego (UCSD), UCLA and the San Diego Veterans Affairs Medical Center reported in the journal Nature Neuroscience that they had partial success in restoring damaged nerve connections in lab rats. This was based on earlier research in which scientists discovered a method to regenerate axons.
Axons are the fibers that connect neurons and carry signals between them, allowing communication between the brain and the nervous system. Axons are damaged or destroyed in spinal cord injuries, causing communication between neurons to be interrupted, which can mean sensory loss and paralysis.
Scientists used a three-part therapy in their study. First, they injected a harmless virus with a chemical growth hormone into the injury site. The growth hormone draws growing axons to the site. Next, they placed a cell graft across the injury site to encourage the young axons to grow. Finally, they stimulated genes in the injured neurons to amplify axon growth.
While the therapy practiced by the team is far from perfect, and will require much more study before being tested on humans, it offers hope to the more than 5.6 million Americans suffering some form of paralysis, 23% of them due to a spinal cord injury.
The team’s success was only partial because, although the axons found their way to the precise spinal injury site and formed connections with other nerve cells, the new neural connections did not have a myelin sheath. The myelin sheath is a fatty sheath that acts as a sort of electrical insulator to assist in the passing of electrical signals between the brain and the body’s nervous system. Since the new connections lacked a myelin sheath, they proved effectively inactive.
Further research is being planned by the same team of scientists to add another step to the already complex therapeutic process in which they hope to encourage the formation of myelin sheaths at the injury site. Although the translation from rats to humans may prove difficult, the creation of the myelin sheath will bring scientists one step closer to fully repairing nerve damage and potentially reversing paralysis.
In Menlo Park, California, the biotech company Geron has plans underway to conduct clinical studies on humans with spinal cord injuries. They will inject embryonic stem cells into spinal cord injury patients in the hopes that the cells will form oligodendrocytes, which in turn assist in the formation of myelin sheaths.
This combination of research inches ever closer to the possibility of full spinal regeneration after a severe injury. While it is nowhere near perfect yet, the promising research continues.