Scientists got nerve cells in mice to regenerate by knocking out genes that halt cell growth, a possible step toward treating brain and spinal cord injuries, according to new research.

Neurons in the central nervous system typically can't grow again once they've matured, and the pathway that regulates their development is silenced when those cells are injured. Researchers at Children's Hospital Boston shut off two genes that inhibit cell growth, then watched to see whether crushed optic nerves in the mice would survive.

Two weeks later, up to 45 percent of the injured neurons were still alive, compared with about 20 percent in the mice that didn’t receive the gene deletions, according to the report in this week's Science. About 8 to 10 percent of the surviving neurons regenerated, an effect seen up to four weeks after the mice were injured.

Scientists have previously tried to regrow neurons in the central nervous system by developing molecules that would block inhibitory antibodies in the cells' environment, a 1999 Scientific American article noted. The new technique attacks the regrowth problem from an alternative premise: that neurons can't regenerate because of how they regulate their own development. Future medications could use that principle to treat brain and spinal cord injuries in people, study co-author Zhigang He said in an e-mail.

Illustration of neuron by iStockphoto/Kiyoshi Takahase