Pregnancy hormone triggers growth of brain cells

When mice mate, the smell centres in their brains are triggered to develop new neurons, Canadian researchers have found. They hope the finding could lead to a way to repair brain cells damaged by disease.

For a decade, researchers at the University of Calgary have been working on what was once thought to be impossible: growing new brain cells. They think they've found a way.

"We propose a naturally occurring hormone that can be introduced into the bloodstream and increase brain cell numbers. It may be an interesting therapeutic molecule," said neurology researcher Prof. Samuel Weiss of the University of Calgary's faculty of medicine.

In animals, including humans, the hormone prolactin surges after sex, and during pregnancy and breastfeeding.

When Weiss and his colleagues injected mice with prolactin, they found cells in the brain's smell centre produced new neurons.

Mammals and insects need their sense of smell to recognize their mate and offspring. Researchers have found transgenic mice that are deficient in prolactin receptors tend to ignore their young.

"If prolactin is administered, ... you initiate the neuro stem cell proliferation equally well in both sexes in mice," said Weiss's Calgary colleague, Dr. Jay Cross of the genes and development research group.

"So it has a much broader potential sort of application, the use of this hormone, and that's quite exciting."

Stem cells have the ability to turn into any type of cell.

The researchers plan to mimic stroke in mice to test the effects of prolactin. They hope to see that new neurons can be sent to other parts of the brain. If it works in mice and eventually in humans, it may be a way to repair injuries from stroke, or other diseases such as Parkinson's or Alzheimer's.

"If we can identify the natural stimulators to make brain cells that are missing, then we may be able to get them to redirect towards areas that are injured in other diseases, other than stroke," said Weiss.

An earlier study published last year in the journal Nature found stem cells in rats redirected neurons toward an injured site. But there were too few to repair the damage.

The Calgary study appears in Friday's issue of the journal Science.

It was funded by the Canadian Institutes of Health Research, the Canadian Stroke Network, the Alberta Heritage Foundation for Medical Research, the Multiple Sclerosis Society of Canada and the Stem Cell Network of the Network of Centres of Excellence.