Stem cell

injured spinal cord.”

A similar approach also has helped mice with epilepsy and Parkinson’s disease.

More than a quarter of a million Americans live with spinal cord injuries, and 17,000 new cases occur each year, according to the National Spinal Cord Injury Statistical Center. More than half of those people go on to develop chronic pain in their limbs, called neuropathy. And nearly all develop bladder problems, which can result in kidney damage.

The spinal cord is the major highway for nerve cells to relay information between the brain and the rest of the body. When the spinal cord is injured, tears and inflammation harm surrounding cells.

“The field has been very focused on restoring patients’ ability to walk, perhaps because that’s often their most visible impairment,” study co-author Linda Noble-Haeusslein, a professor of physical therapy and rehabilitation at UCSF, said in a statement.

But a recent study showing that patients complained of pain and loss of bladder control more than paralysis “suggested that we had really missed the boat as a field,” she said. “It caused us to dramatically shift what we do in the lab.”

The cells used in the study, called neurons, were grown from human embryonic stem cells — the body’s building blocks, capable of generating more than 1,000 different types of adult cells.

They aren’t just any garden-variety neuron. These cells have the ability to inhibit, rather than excite, the neural network of the spine. That’s important because the pain and loss of bladder control are believed to be caused by overactivated neural circuits.

The healthy body keeps this excitable circuitry under control. But inflammation caused by a spinal cord injury causes a loss of this control.

The UCSF team grew the replacement cells in a South San Francisco biotech lab of Neurona Therapeutics, founded by study co-author Cory Nicholas and Kriegstein, UCSF professor of developmental and stem cell biology. The company hopes to massproduce these cells for use in future clinical trials.

They injected the young human cells into the spines of mice about two weeks after injury. They targeted the thoracic region — about halfway up the spinal cord — because that’s a common site of injury for humans. But they were careful not to inject the young cells directly into the injured areas because that is a toxic place full of inflammation.

Remarkably, over the next six months the human cells matured, migrated toward the site of the injury and made connections with the spinal cords of the mice.

Compared with untreated mice, the treated rodents showed significantly less hypersensitivity to touch and painful stimuli and reduced abnormal