A pregnancy hormone may help repair the damage to nerves caused by multiple sclerosis, Canadian research suggests.
Protective myelin is stripped away by MS
The Journal of Neuroscience study, by the University of Calgary, may explain why MS tends to go into remission while women are pregnant.
Working on mice, the researchers found the hormone - prolactin - encourages production of myelin, the fatty substance that protects nerve cells.
Myelin is degraded by MS, damaging nerves' ability to transmit messages.
The latest finding raises hopes of new treatments for MS, and other neurological disorders, which potentially reverse, rather than stabilise symptoms.
The researchers showed that prolactin was directly responsible for the formation of new myelin in the brains and spinal cords of pregnant mice.
When mice with MS-like nerve damage were injected with the hormone, their myelin was also repaired.
Immune system attack
MS is caused by the body's immune system attacking the myelin surrounding nerves. This leads to progressive loss of sensation and movement.
Lead researcher Dr Samuel Weiss said: "It is thought that during pregnancy, women's immune systems no longer destroyed the myelin.
"However, no previous study has tested whether pregnancy actually results in the production of new myelin, which may lead to improvement of symptoms."
The researchers said more work was needed, but they are hopeful human trials can take place within the next several years.
Dr Fred Gage, of the Salk Institute, said: "Agents promoting remyelination will be beneficial not only for typical demyelinating diseases like MS, but also for many other neurological disorders, such as spinal-cord injuries and stroke."
The researchers found pregnant mice had twice as many myelin-producing cells (oligodendrocytes) as virgin mice, and continued to generate new ones during pregnancy.
They chemically destroyed myelin around nerve cells, and found the pregnant mice had twice as much new myelin as the virgin mice two weeks later.
Introducing prolactin in virgin mice mimicked the effects of pregnancy on myelin production and repair in the animals.
John Habkirk, of the Multiple Sclerosis Resource Centre, said: "This research looks to be giving scientific credence to something that people affected by MS have been able to identify for a long time.
"Women nearly always have a much easier time with their MS during pregnancy and at last some research is starting to show precisely why."
MS Trust chief executive Chris Jones said: "It is already well documented that sex hormones such as oestrogen can influence the development and course of MS.
"The suggestion that this can also have a role in replacing myelin is encouraging, but we will have to wait and see if the studies in mice with the experimental equivalent of MS will translate into a successful treatment for people with MS."
MS Society head of research Dr Lee Dunster agreed that the study raised the possibility that prolactin could potentially be used to treat MS.