Walking ability in paralyzed rats improves following treatment.

Rats with spinal cord injuries regained 70% of their normal walking function with a 3-part treatment, according to a report in the June issue of Nature Medicine.

The results of the study, conducted by researchers at the University of Miami in Florida, far exceeded expectations, said the principal researcher, Mary Bartlett Bunge, MD.

"It opens up a potential new avenue of treatment for human spinal cord injury," said Bunge, who declined to speculate when human trials might be attempted.

The spinal cord carries messages between the brain and the muscles through a network of nerve cells. Normally, chemical signals prevent those nerves from regrowing, resulting in paralysis when the network is severed by an injury. Regrowing nerve cells and reconnecting them is the holy grail of spinal cord research.

The Miami study involved hundreds of animals with crushing injuries to the thoracic region of the spinal cord, which mainly causes loss of control of the legs and is the most common form of injury among the 243,000 people in the United States living with spinal cord injuries, the researchers said.

They transplanted cells known as Schwann cells from the peripheral nerves, where regeneration does occur, to create a bridge across the damaged area of the spinal cord and promote the growth of axons, the nerve fibers that transmit messages. Those cells also make the protective myelin sheath that insulates some nerve fibers.

In earlier research, such grafts did promote the growth of new nerve fibers across and through the damaged areas of the spinal cord, but they stopped growing too soon.

So researchers combined the grafts with 2 additional treatments-injections of cyclic AMP, a messenger molecule that guides the nerve cells to grow their connecting fibers, and Rolipram, which prevents the breakdown of cyclic AMP.

Because of the rolipram, "cyclic AMP hangs around longer and can be more effective," Bunge said.

Rolipram was developed as an antidepressant by Germany's Schering AG and is also being investigated as a possible treatment for multiple sclerosis. After 8 weeks, the rats that did not receive the treatment could occasionally take a halting step but could not take one step after another, Bunge said. In contrast, those given the treatment had regained 70% of their walking function, "a striking improvement," Bunge said. They could step consistently and had better fine motor control and coordination.

"Each of the pieces of the (Miami) strategy have been hailed as 'promising' in earlier reports, but the behavioral effects were not huge. With the right combination, the sum is now proving to be much greater than the parts," said Naomi Kleitman, MD, a program director for spinal cord injury research at a branch of the National Institutes of Health.