Scientists from the University of Chicago have discovered how nerve cells are directed to grow down the spinal cord, a finding that could prove highly important in repairing spinal cord injuries with stem cell technologies.

The report appears in the September issue of the journal Nature Neuroscience.

For the body to work properly, data must flow between the body and the brain in both directions, via the spinal cord.

For instance, information that the skin is cold is sent up the spinal cord to the brain. The brain computes “I am cold” and then sends signals back down the spinal cord to the muscles, coordinating them so that a person can pick up and put on a coat.

Much like the electricity grid, the neuronal wiring in the spinal cord needs to be built up so there are no significant gaps in the system that could prevent an electrical message from getting through.

The new research shows the same family of chemical signals that attracts developing nerves in embryos to grow up the spinal cord is also responsible for sending them in the opposite direction.

Nature’s Efficiency

“This is a remarkable example of the efficiency of nature,” said Yimin Zou, assistant professor of neurobiology, pharmacology, and physiology at the University of Chicago. “The nervous system is using a similar set of chemical signals to regulate axon traffic in both directions along the length of the spinal cord.”

Axons are long, narrow extensions that nerve cells send out to find and connect with other neurons. They are tipped with receptor molecules, which monitor the concentration of proteins known as Wnt proteins.

In 2003, the Chicago researchers found that nerve cells carrying sensory information toward the brain have axons tipped with receptor molecules called Frizzled3.

Frizzled3 responds to an increasing concentration gradient of Wnt proteins and therefore tells the nerve cell to grow up the spinal cord and make connections so it can pass sensory information toward the brain.

Different Receptor Found

In the September paper, the scientists say that a different receptor, called Ryk, is present on the axons of nerve cells carrying information away from the brain.

Ryk receptors cause the axon to respond to Wnt proteins in the opposite way, growing toward lower concentrations of the proteins and therefore causing the axons to seek connections with other nerve cells further away from the brain.

According to Mr. Zou, Wnt proteins might one day be used as a way to guide transplanted nerve cells, or even embryonic stem cells, to repair broken connections in the spinal cord.

“It could revolutionize treatment of patients with paralyzing injuries to these nerves,” he said. “Although half the battle is acquiring the right cells to repair the nervous system, the other half is guiding them to their targets where they can make the right connections.”

Currently, Menlo Park, California-based Geron is considered the forerunner in spinal cord repair therapies.

The company has spent more than $100 million funding research at several universities in the United States and United Kingdom, including the University of California at San Francisco, the University of Wisconsin, JohnsHopkinsUniversity, as well as the University of Edinburgh (see Stem Cells: U.S. May Lose Lead).

The University of Chicago research was funded by the National Institute of Neurological Disorders and Stroke, the Schweppe Foundation, the RobertPackardALSCenter at JohnsHopkinsUniversity, the University of Chicago Brain Research Foundation, and the JackMillerCenter for Peripheral Neuropathy.