Scientists from UCLA, Harvard Medical School (Boston) and the Swiss Federal Institute of Technology (Lausanne, Switzerland), have demonstrated, in rodents, that it is possible to reconnect severed spinal cord neurons by manipulating their growth processes.

Prior to this, the belief was that the scar tissue resulting after a spinal cord injury created a barrier that prevented damaged neurons from regrowing. However, this new research has shown the potential to overcome this barrier and reconnect severed spinal cord neurons.

"These insights are important for understanding the mechanisms of injury and regeneration that may one day be applied to develop potential treatments for spinal cord injury," said Lyn Jakeman, Ph.D., program director, National Institute of Neurological Disorders and Stroke (NINDS), which supported the research.

The study incorporates three components of the regrowth process.

The first involves genetics. The researchers injected mice and rats with viruses that contain genes capable of reactivating the growth program that produced the original connections. This enabled the neurons to revert to a state in which axon growth was possible. Axons are the projections that neurons use to send signals, and are often severed when spinal cord injuries (SCIs) occur, causing lost sensation and paralysis below the site of the injury.

The second is creating a viable pathway for the axons to travel along. For this, the scientists injected a gel containing a combination of growth-promoting proteins that increased axon-supportive molecules to create that path across the injury.

The third component required mimicking chemoattractants, proteins released by neurons during the growth process, that act as targets for the axons to follow in order to grow through the injury site and connect properly on the other side.

When utilizing all three steps in order, neurons grew successfully and tens to hundreds of axons reconnected with neurons through the scar tissue. However, creating these connections is only the first step in healing SCIs. Further work would need to be done for actual mobility to improve. "We would expect that these regrown axons would behave very much like the new axons we see in development," explained Michael V. Sofroniew, M.D., Ph.D., professor at the Brain Research Institute at UCLA and senior author of the study published in Nature. "Much like a newborn must learn to walk, these newly formed circuits will probably require training before functional recovery can be seen."

According to the National Spinal Cord Injury Statistics Center, based at the University of Alabama at Birmingham, approximately 288,000 and as many as 358,000 people living in the U.S. have spinal cord injuries, with about 17,700 new cases each year. The goal of the research is to restore connections severed by SCI to provide functional recovery for those affected by spinal cord trauma.