Antibodies enhance spinal nerve regrowth.

Antibodies enhance spinal nerve regrowth 

With the help of novel antibodies that block nerve-growth inhibitors, scientists have stimulated uprecedented nerve regeneration in the severed spinal cords of rats. New fibers grew as much as 11 millimeters in three weeks -- about 10 times the regrowth achieved without the antibodies.

Althouugh biochemical hurdles preclude immediate application in humans, the experiments provide evidence that scientists have overcome one of the major roadblocks to central nervous system (CNS) repaidr.

Indeed, the results effectively banish the already-crumbling notion that the vertebrate central nervous system is incapable of significant regrowth. Moreover, they strengthen the concept -- until now unproved in animals -- that the fate of damaged CNS nerves rests not on growth factors alone but one the delicate balance between growth-enhancing and growth-inhibiting substances.

Martin E. Schwab and Lisa Schnell of the University of Zurich, Switzerland, severed the cortico-spinal tract -- a bundle of nerve fibers in the spinal cord -- in 41 rats. Control rats given no antibodies or antibodies unrelated to nerve regrowth made feeble attempts at nerve regeneration, with new nerve sprouts rarely extending beyond 1 mm.

But rats receiving doses of an antibody that inactivates naturally occurring nerve-growth inhibitors showed "massive sprouting" of new nerve fibers at the injury site, the researchers report in the Jan. 18 NATURE.

Schwab and his colleagues discovered several years ago that growth-inhibiting proteins reside in the myelin sheath surrounding CNS cells. In 1988, the group used mice to produce antibodies against these proteins. Experiments on cultured nerve cells showed then that the antibodies enhanced nerve growth by inactivating the inhibiting substances.

The new experiments are the first to achieve this effect in live animals, says neuroscientist Albert Aguayo at McGill University in Montreal, who calls the reseach "very promising, very exciting." He notes that nerve regrowth must extend beyond 11 mm to reach very distant targets in humans. "But for rats," he says, "distances such as these are quite substantial."

The results illustrate the "very prominent role" of inhibiting substances in the control of CNS development, Schwab told SCIENCE NEWS. He says researchers know little about the potent proteins, which appear late in fetal development and apparently engage in a "subtle, antagonistic interplay" with several naturally occurring nerve-growth-proteins identified in recent years. By suppressing sprouting, the inhibiting factors may serve as "guardrails," he

adds, keeping new nerve endings from straying outside their proper paths.

Having originated in mice, the experimental antobodies would trigger a dangerous immune response if injected into humans, Schwab says. But once scientists gain a beter understanding of their structure and mode of action, it should be possible to synthesize human-compatible versions, he adds. He theorizes that scientists will someday accomplish significant CNS regeneration in humans through the combined use of growth inhibitors and promoters.