NEW ORLEANS (AP) - Scientists say they have restored sensation to lab rats by repairing nerves severed and crushed at the spine, a breakthrough that may someday allow doctors to help people with disabling spinal injuries.

The technique involves implanting a "bridge," made of fetal cells, to guide regrowth of the nerves connecting -the rat's hind leg to the spinal cord, said Dr. Jerry Silver of Case Western Reserve University in Cleveland.

"We believe we really have regeneration into the spinal cord" for the first time, he said. Previous attempts to get nerves to grow back into the spinal cord failed because scar tissue got in the way.

Silver is not working with the spinal cord itself, only with the nerve that carries impulses from a rat's right hind leg into the spinal cord. Scientists generally believe the spinal cord cannot be repaired after injury.

"My philosophy is to start with something simple and get more complex," Silver said earlier this month.

Silver, a neuroscientist with a doctorate in anatomy, was to present his findings Monday at a
symposium here of the Society for Neuroscience.

Dr. Richard Jed Wyatt of the National Institute of Mental Health, a leading researcher in the field, said the finding was arousing excitement among scientists.

Silver said he and his colleagues, including postdoctoral student George Smith and neurosurgeon Michel Kliot of Columbia Presbyterian Hospital in New York, began by cutting and crushing roots of the sciatic nerve.

Cutting the root just outside the fifth vertebra produces effects much like those that occur when a ruptured spinal disc crushes the root; toes can be moved but have no sensation, Silver said.

"People with this problem limp and their foot hangs down. They have problems with their toes gripping the ground and they fall. They can't wear high heeled shoes," he said.

Then cells called astrocytes were used to try to repair damage at the fifth vertebra.

In embryos, astrocytes build what Silver described as highways for the long fibers through which information goes to and from a nerve cell. But in adults he said, scar tissue blocks off damaged nerve cells.

He said his research team made bridges from a new porous polymer coated with glia -- the long nerve fibers -- of astrocytes from rat embryos.

The bridge is shaped like a tiny pennant, with the pole going into the nerve root and the flag into the spinal cord, he said.

He said most animals get some feeling back within a week or so, but those treated with embryonic astrocyte glia seemed to return much closer to normal.

They were also the only rats that lost all feeling again when the nerve root was cut a second time--indication that the nerve had indeed grown back, he said.

"The astrocytes break down the scar and provide an appropriate highway for growth. That's why this works," he said.

Of 44 rats tested so far, he said, 13 were treated with fetal astrocytes. Of those 13, all regained feeling after treatment, but only seven lost it again after the nerve was re-cut. "We have to figure out why those others don't work," he said.