New Orleans — For the 270,000 people in the United States who live with spinal-cord injuries, the hope of walking again is never far from their minds. It has, sadly, been farther from reality, but today it seems a little bit closer. Some unusual technologies—electrodes placed in the brain, far from the injury, and a gas that most people think of as toxic rather than healing—are showing promise in early tests.
Studies of those tests, presented on Monday at the Society for Neuroscience meeting here, have been limited to animals, but they show how neuroscientists are rethinking nerve damage once deemed permanent and crippling.
“Most of these injuries are not complete. They are partial,” said Jacqueline Bresnahan, a researcher in the department of neurological surgery at the University of California at San Francisco. “Some connections remain.” It may be possible to take advantage of those remaining links, boosting them to make dormant limbs move, said Ms. Bresnahan, who was not involved in the studies.
One of those techniques builds on something called deep-brain stimulation, now used successfully to limit disabling tremors in patients with Parkinson’s disease. To do it, surgeons implant hair-thin electrodes in regions near the base of the brain, and the pulses interrupt some errant signals in those regions that are responsible for involuntary jerks that render limbs useless.
In injured rats, Brian Noga of the University of Miami School of Medicine took aim at a different target. In the middle of the brain, there is an area involved in movement called the mesencephalic locomotor region.
“We think it initiates motion, and it has really giant neurons with projections that go far down the spinal cord,” said Mr. Noga, who is a scientist at the university’s Miami Project to Cure Paralysis. Stimulating those neurons, he and his colleagues thought, could send signals past the site of an injury and get limbs to move.
They tested the theory in three groups of rats, some of which had mild spinal-cord damage, some moderate, and some severe. They inserted the electrodes and tested the rats on a treadmill. “In the mildly injured animals, their speed was equal to animals that had not been injured at all,” Mr. Noga said. And rats that had moderate and severe wounds in their spinal cords, and that had not been able to walk, were able to step forward again when the researchers supported their weight.
The researchers also tested endurance: With stimulation and weight support, even severely injured rats doubled the distance they could walk. “These results challenge a lot of assumptions” about the permanence of spinal-cord injuries, as well as the ability to intervene, Mr. Noga said. “We think the stimulation, which is really very mild, puts the brakes on cell signals that inhibit movement, and at the same time it adds gas to cells that drive locomotion.”
Gas—real and not metaphorical—was another potential therapy discussed at the meeting. Carbon monoxide is usually thought of as a pollutant and a household danger if you inhale too much of it. But a little of it seems to protect injured spinal-cord nerves and help them heal, said Inbo Han, a researcher in the department of neurosurgery at Harvard Medical School.
That’s because direct trauma isn’t the only damage that occurs in spinal-cord injuries. After the trauma, partly shredded neurons try to pull themselves together, only to be thwarted by the body’s own immune response, which sends in scavenger cells in a misguided attempt to scoop up the injured cell parts. The result is a scar, instead of re-knit nerves.
Carbon monoxide dampens that immune reaction, keeping the cells away from the wound. Mr. Han and his colleagues put rats with severe spinal-cord wounds in a chamber where, every day for 12 days, they breathed air laced with small amounts of carbon monoxide for one hour. Three different groups got different levels of gas: 100 parts carbon monoxide per a million parts regular air; 250 parts per million; and 500 parts per million. (In humans, those levels bring on headaches within one or two hours. A level of 1,500 parts per million can be deadly. Various U.S. health agencies recommend limits between 25 and 50 parts per million over eight hours.)
The more gas, the more healing. All the rats got better, moving their hind limbs more easily and showing more closure of their wounds. The rats that breathed 500 parts per million did best, Mr. Han said. They also showed a reduction in those scavenger cells, and more of their motor neurons survived.
These are small steps. But as attempts to help people who can’t take any steps, they matter.
(Photo courtesy Don.Wing45 under Creative Commons license)