Canadian researchers have used stem cells to repair spinal cord damage in laboratory rats, restoring significant mobility in the animals and bringing the search for a human therapy another step closer.

A team led by Toronto neuroscientist Dr. Michael Fehlings extracted stem cells from adult mice, which were transplanted into rats whose spines had been crushed. The stem cells developed into one type of cell destroyed by the injury — the kind that produces myelin, the insulating layer that cocoons the bundle of nerve fibres that make up the cord.

Injuries that crush or compress the spinal cord destroy its ability to regenerate myelin-forming cells, leading to paralysis. Without the myelin sheath, "nerve fibres don't conduct the signals, they kind of short out and you don't get signals crossing," said Fehlings, medical director of the Krembil Neuroscience Centre at Toronto Western Hospital.

Dr. Oswald Steward, director of the Reeve-Irvine Research Centre for spinal cord injury at the University of California, said the concept of using stem cells for spinal cord cell regeneration has been applied by other scientists. But Fehlings' work "breaks new ground in a couple of ways": by showing that adult stem cells work as well as the more ethically controversial fetal or embryonic stem cells and that the drug minocycline improved their survival, Steward said.

Fehlings said, however, that his transplanted cells, called neural precursor cells, are not as versatile as embryonic stem cells because they can give rise only to cells of the nervous system.

In Fehlings' experiments, rats whose crushed spinal cords were injected with adult stem cells and given a cocktail of drugs — growth hormone, cyclosporine to prevent rejection and the anti-inflammatory minocycline — were found to walk with better co-ordination and weight-bearing ability.

As well, researchers were able to get those results even when the stem cells were injected two weeks after the injury. Current therapies that attempt to save spinal cord tissue from trauma-induced destruction must be given within hours of injury.

"Our strategy wasn't to get perfect regeneration or to try to regrow the whole spinal cord," said Fehlings. "Our approach was really to try to replace one missing cell type.

The success appears to be due to minocycline, which reduced inflammation of the spinal cord and limited cell damage, said Fehlings, adding it also seemed to boost survival of stem cells.

Someday, stem cells might be taken from the brains of patients with spinal cord injuries for their own treatment, Fehlings said. His study appears in today's edition of The Journal of Neuroscience.