In one study, newborn rats regained nearly full function after sections of their spinal cords were removed and replaced with transplants from fetal animals. In the second, severed nerve fibers regrew in rat spinal cords that had been cut nearly in half and then treated with growth-stimulating biochemicals.

After removing a 2-millimeter-long section of cord, the researchers grafted into the gap pieces of cord from fetal rats. The rat spinal cord - like all spinal cords - has "topographic" organization. Cut in cross section, it has functional north, south, east and west quadrants. In some of the rats the researchers placed the grafts in the normal orientation, and in others abnormally.

The body also manufactures chemicals that inhibit nerve growth. Such inhibition is essential for maintaining the dense, highly ordered architecture of the nervous system. The researchers injected the brains of some of the experimental animals with a substance that inactivates one of those inhibitory chemicals. In the animals that received inhibitor injections and a specific growth factor called neurotrophin-3 (NT-3), nerve fibers in the cut half of the cord grew down the intact half.