June 12th, 2002 12:37:09 -0400 (Reuters Health)
By Alison McCook
NEW YORK (Reuters Health) - Adding a particular molecule to nerve cells before severing them helps them to regrow damaged structures following the injury, according to new research.
A modified version of this technique may one day enable doctors to treat people who suffer from paralysis and other conditions following spinal cord injuries, the authors note. However, the experiments were conducted in rats, and researchers would not be able to immediately apply this technique to humans.
"But for now, the exciting thing is that we have a manipulation that can give us robust regrowth (in nerve cells), and that we can work with," study author Dr. Marc Tessier-Lavigne of Howard Hughes Medical Institute at Stanford University in California told Reuters Health.
A group of US researchers performed experiments on rats in which they enabled the rats to regrow the nerve cell structures that normally connect the cells to the spinal cord. The researchers added a cell signaling molecule called cyclic AMP (cAMP), which has been shown to help nerve cells regrow in test tubes, to rats, then severed the nerve cells' connections to the spinal cord.
Although mammals such as rats and humans are not usually able to repair those types of injuries, the structures connecting the nerve cells to the spinal cord grew back.
"We see quite dramatic regeneration," Tessier-Lavigne told Reuters Health.
Nerve cells contain a cable-like structure called an axon, which connects them to the spinal cord. Those axons can be a meter long, and when they are severed, the fragment closest to the spinal cord degenerates. The cellular environment surrounding the severed axon is such that it prevents the regrowth--nerve cells will try, but as Tessier-Lavigne described it, the cell eventually "stalls out."
However, previous research that tested severed nerve cells in a test tube found that adding cAMP to the severed cells enabled the axon fragments to regrow. But still, an important question remained: "Does it work in the more complex environment of the intact animal?" Tessier-Lavigne asked.
Now, in two papers published in the June 13th issue of Neuron, the researcher, along with Dr. Marie T. Filbin of the City University of New York and Dr. Allan I. Basbaum of the University of California, San Francisco and their colleagues, showed that, in live rats, severed nerve cells given cAMP can regrow their damaged axons.
However, Tessier-Lavigne cautioned that there are many reasons why these results cannot be immediately applied to humans with spinal cord injuries. The investigators administered cAMP directly to the specific nerves before they were severed, a technique impossible in an already injured person. Furthermore, the researchers studied the potential for regrowth in sensory nerve cells, which are similar, but not identical, to the motor nerve cells implicated in paralysis.
Finally, the researcher explained that he and his colleagues only discovered that the nerve axons regrew, and did not measure whether the structures had been able to make the right connection with the spinal cord, allowing the rats to regain their lost functioning.
However, Tessier-Lavigne noted that he suspected motor nerve cells involved in movement could respond to cAMP as sensory nerves had, and nerve structures that regrow can often connect well to the spinal cord.
The next step, he added, is to see whether administering cAMP after an injury can enable the nerve cells to regrow, as well.
SOURCE: Neuron 2002;34:885-893, 895-903.
Copyright © 2002 Reuters Limited