The researchers injected a modified version of human embryonic stem cells that were cultured by Hopkins’ stem cell pioneer, John Gearhart, into the spinal fluid of the paralyzed animals. Three months later, most of the injected rats could flex their hips and place feet firmly enough to bear weight. A few of the rats could actually hobble.

“As thrilling as that was, the most dramatic finding,” says Kerr, “was proof that stem cells migrated to the ventral horn of the spinal cord, exactly where neurons had died.” Additionally, the cells displayed molecular nerve cell markers and further, sent axons outward. “They even look like motor neurons.”

Although the rats improved, Kerr believes they’ll plateau far short of normal. “To regain full movement, you’d likely have to reconstitute the entire system. The thousands of axons at the spinal cord level, each with its unique destination.

But Kerr thinks nervous systems can make do with considerably less. “We may not have to replace all the original circuitry.”

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