The scientists embedded neural stem cells in a matrix of fibrin (a protein key to blood clotting that is already used in human neuron procedures), mixed with growth factors to form a gel. The gel was then applied to the injury site in rats with completely severed spinal cords.
“Using this method, after six weeks, the number of axons emerging from the injury site exceeded by 200-fold what had ever been seen before,” said Mark Tuszynski, MD, PhD, professor in the UC San Diego Department of Neurosciences and director of the UCSD Center for Neural Repair, who headed the study. “The axons also grew 10 times the length of axons in any previous study and, importantly, the regeneration of these axons resulted in significant functional improvement.”
In addition, adult cells above the injury site regenerated into the neural stem cells, establishing a new relay circuit that could be measured electrically.
“By stimulating the spinal cord four segments above the injury and recording this electrical stimulation three segments below, we detected new relays across the transaction site,” said Tuszynski.
To confirm that the mechanism underlying recovery was due to formation of new relays, when rats recovered, their spinal cords were re-transected above the implant. The rats lost motor function – confirming formation of new relays across the injury.