After an injury in the brain or spinal cord, neurons start to regrow but are stopped in their tracks by newly scarred tissue. A new method helps rat neurons get around that roadblock. The method could one day help coax cells to partially regrow and form new connections in patients with serious spinal cord injuries.
The troublesome scar tissue is made by neural support cells called astrocytes. These cells also create more than just a physical barrier. In earlier work, a team led by neurobiologist James Fawcett of Cambridge University showed that astrocytes release chemical signals called chondroitin sulfate proteoglycans (CSPGs) that tell nascent neurons to stop growing.
Inspired by their discovery, Fawcett and his colleagues thought they might be able to help shaky new axons regrow. First, they surgically severed brain tissue in rats. Then they infused a CSPG-digesting enzyme into the injured tissue. After 11 days, the team examined how well the nerves had regrown. In animals treated with the enzyme, called chondroitinase ABC, neurons extended more than 6 times as many fibers as in rats infused with a salt solution. The axons also tended to grow in the right direction: More than 4 times as many axons grew into the correct brain structure in the treated rats compared to the untreated ones, the team reports in the May issue of Nature Neuroscience. And in recent unpublished work, the researchers showed that strategy works in rat spinal cords as well as rat brains, Fawcett says.
"It's an excellent extension of previous research," says neurobiologist Jeffrey Goldberg of Stanford University. But he and other experts caution that in humans, the method will have to be combined with methods that remove other key roadblocks to nerve regeneration. "Spinal cord injury is not going to be solved by one major discovery, says Federico Girardi, director of research and education at the SpineCare Institute at the Hospital for Special Surgery in New York City. "It's going to be a lot of small discoveries that will make a big difference."