A hormone produced during pregnancy spontaneously increases myelin, which enhances signaling within the nervous system, and helps repair damage in the brain and spinal cord, according to new animal research.

The findings, published in the February 21 Journal of Neuroscience, indicate that the hormone prolactin promotes an increase in myelin production and may have a use in treating multiple sclerosis (MS).

In MS, affecting about 2.5 million people worldwide, the body's own immune system attacks myelin, which insulates nerve cells and plays a critical role in the speed at which messages are transmitted from cell to cell. Reduction in myelin leads to a progressive loss of sensation and movement in MS patients.

"Agents promoting remyelination will be beneficial not only for typical demyelinating diseases like MS," says Fred Gage, PhD, of the Salk Institute, "but also for many other neurological disorders, such as spinal cord injuries and stroke." Gage did not participate in the study.

The research was based on evidence showing that multiple sclerosis, which is more common in women than men, goes into remission when women become pregnant. "It was thought that during pregnancy, their immune systems no longer destroyed the myelin," says study author Samuel Weiss, PhD, at the Hotchkiss Brain Institute of the University of Calgary. "But no previous study has tested whether pregnancy actually results in the production of new myelin, which may explain improvement of symptoms."

Comparing pregnant and virgin female mice of the same age, Weiss's team counted hundreds of cells in their brains and spinal cords. They found that the pregnant mice had twice as many myelin-producing cells, called oligodendrocytes, and continued to generate new ones during pregnancy. After giving birth, these mice also had 50 percent more myelin coating their nerve cells.

The researchers also showed that pregnancy repaired nerve cells faster where the myelin had been chemically destroyed: Pregnant female mice had twice as much new myelin two weeks after damage. Finally, they found that prolactin mimicked the effects of pregnancy, increasing both myelin production and repair. This suggests prolactin, which increases during pregnancy, may help induce the making of new myelin.

Should future tests of prolactin in animal models of MS prove successful, Weiss says the hormone will be ready for testing as a treatment for people with MS.

Written from a news release by Society for Neuroscience.