Unblocking the Highway

Growing axons reconnected
with the spinal cord
© University of Erlangen

The body's spinal cord is like a super highway of nerves. When an injury occurs, the body's policing defences put up a roadblock in the form of a scar to prevent further injury, but it also stops all neural traffic from moving forward.

First, the researchers from Case Western Reserve University, Drexel University and the University of Arkansas regenerated the severed nerve fibres, also called axons, around the initial large lesion with a segment of peripheral nerve taken from the leg of the same animal that suffered the spinal injury. Next, they jump started neural traffic by allowing many nerve fibres to exit from the end of the bridge.

This was accomplished, for the first time, by using an enzyme that stopped growth inhibitory molecules from forming in the small scar that forms at the exit ramp of the bridge, where it is inserted into the spinal cord on the other side of the lesion. This allowed the growing axons to reconnect with the spinal cord.

Jerry Silver, professor of neurosciences at the Case School of Medicine said the medical community had assumed that the cut axon tips died when they hit the scar wall. However, in prior research in his laboratory it was discovered that axons are alive and continue to attempt to grow for years. Silver describes them as "trucks stuck in mud going no where." This explains why some people gain some movement back or come out of comas after many years as the nerve fibres sprout through weakened or remodeled areas of the scar.

About 16 years ago, Silver also made another find that proteoglycans, a sugary protein, is present at the site of spinal cord lesions. He also knew that a particular enzyme from the bacteria Proteus vulgaris, called chondroitinase, might dismantle the proteoglycans by clipping their sugar branches, thereby preventing the scar wall from building.

MEDICA.de; Source: Case Western Reserve University