Delayed surgery aids spinal cord repair. (Science News of the week).

Holding off on spinal cord surgery until a few weeks after an injury, rather than attempting it immediately, improves the chances of regaining some powers of movement lost because of the injury, a new study of rats finds.

Spinal injuries damage neurons. These cells' long tendrils, called axons, then can't carry signals from the brain to muscles and other tissues, a formula for paralysis.

Scientists at Georgetown University Medical Center in Washington, D.C., attempted to repair severed spinal cords in rats by implanting spinal tissue from fetal rats either immediately after an injury or 2 or 4 weeks later. For 14 days, all the animals also received infusions of neurotrophins--naturally occurring chemicals that induce axons to grow--or an inert substance.

The researchers then observed whether the animals regained movement of their paralyzed hind limbs. Starting 3 weeks after surgery, rats getting delayed surgery and neurotrophins began using the limbs to stand, walk, and climb stairs markedly better than did rats that received prompt surgery as well as the neurotrophins, the scientists report in the Dec. 1 JOURNAL OF NEUROSCIENCE. Rats not getting the neurotrophins failed to improve.

Examination of the animals at least 2 months after surgery revealed that rats getting a combination of delayed transplants and neurotrophins grew more and longer axons than the other rats did, says study coauthor and neuroscientist Barbara S. Bregman. The researchers also traced dye injected into the severed nerves and found that it traversed the injury site in animals getting delayed surgery and neurotrophins. That finding suggests that the regrown axons were carrying signals, Bregman says.

Injured animals can retain some movement that doesn't require axon regrowth, Bregman says. To rule out this explanation for the recovery, she and her colleagues recut the spinal cords in some rats. That abolished the regained movement, indicating that axon regrowth was responsible for the initial recovery.

The work complements other research that shows that damaged spinal cords treated with fetal tissue can regenerate weeks or months after injury. It also adds solid evidence that such repair can lead to recovery of movement in rats, says neuroscientist John D. Houle of the University of Arkansas for Medical Sciences in Little Rock.

The best time for fetal-tissue transplants remains uncertain, despite the new study. Immediately after injury, a transplant enters "a really hostile environment" rife with immune cells and inflammatory proteins, says neuroscientist Scott R. Whittemore of the University of Louisville in Kentucky. These clear out over time, but new scar tissue makes axon reconnection difficult.

Removing scar tissue, as Bregman did, opens the way for a tissue transplant but risks more injury to the site, Houle says.

Such surgery in people remains rare and experimental, in part because of these uncertainties and ethical issues regarding the use of fetal tissue. Still, this study "brings hope back for people with such chronic injuries," says neuroscientist Martin Oudega of the University of Miami School of Medicine.