sex heals your brain?

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Sexual peak releases hormone that regenerates brain: research
Quest for prolactin

Brad Evenson
National Post

Friday, January 03, 2003
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Great sex holds the ingredients to heal the brain damage caused by strokes or degenerative diseases like Huntington's, a new Canadian study suggests.

The study, published today in the journal Science, shows prolactin, a natural hormone produced after orgasm and childbirth, stimulates the birth of thousands of new cells in the forebrains of mice. "The experiment that we did ... suggests that mating itself may enhance neurogenesis," said study author Sam Weiss, a professor of medicine at the University of Calgary.

Last year, scientists showed the human brain makes a faltering effort to heal itself after a stroke by sending new cells to the damaged area. Dr. Weiss says infusing patients with prolactin could boost this mechanism.

"Because it can be added directly into the bloodstream to produce the brain effect, we are preparing to test how it might help stroke recovery," he said.

If the new cells reach the damaged area before it scars, the effects of strokes could be reduced. Similar approaches could someday be used to treat other neurodegenerative diseases, including Parkinson's and Alzheimer's.

Just over 10 years ago, Dr. Weiss made newspaper headlines around the world when he discovered the adult brain contains stem cells, the primitive ancestors of new brain cells. But what caused these cells to multiply and where they migrated in the brain remained a scientific mystery.

A few years ago, however, the behaviour of female mice with an impaired sense of smell offered a clue.

"They seemed to be ignoring their young," Dr. Weiss says.

Virtually all animals rely on smell, or olfaction, for sexual attraction and for rearing young.

Humans can distinguish between up to 10,000 different odours, from dung to Chanel No. 5. Smell is particularly important to mothers. Women with morning sickness suddenly become sensitive to strong odours, and most mothers rely on smell for recognizing and bonding with their offspring.

So if new brain cells could be born in adults, Dr. Weiss suspected it is probably in the olfactory region of pregnant females. The hunch proved correct.

"We found that during the first week of pregnancy there was a spike in brain cell production," he says.

The new neurons then migrated to the olfactory bulb, an area at the front of the brain, where they are necessary for the adult mouse to remember new odours and to distinguish them from other similar odours.

Several weeks after conception, the new growth receded, then spiked again when the mice delivered their offspring.

However, pregnancy was not necessarily the key ingredient.

When mated with sterile males, the female mice also produced thousands of new brain cells a week after sex. "Since there was no embryo, the cause had to be a surge of hormones," Dr. Weiss says.

The researchers soon zeroed in on prolactin.

Intriguingly, men also make prolactin after orgasm. This may explain why the man in the celebrated Viagra commercial stops to smell the roses after a night of sex -- the number of scent cells in his brain has doubled. It may also explain why the perfumes and colognes of lovers often have such deep emotional resonance in their memories.

"It certainly intrigues one to ask the question ... might [prolactin] be playing a role in mating behaviours and in relationships?" Dr. Weiss says.

Creatures with minor differences in their hormone systems have much different romantic habits. Prairie voles are monogamous and mountain voles are polygamous. Why the difference? Zoologists point to a small variation in how the tiny rodents' cells respond to the hormone vasopressin.

Researchers are also focusing on the links between smell and brain disease.

For example, one of the first symptoms of both Parkinson's and Alzheimer's diseases is a loss of olfaction. Scientists believe if they can increase the population of stem cells in the brains of such patients, they may reduce the impact of these diseases.

Although new cells normally travel to the olfactory bulb, they change direction in the event of a brain injury.

"This really holds out the chance that the brain in adults is plastic enough to make a repair," said Robert Dempsey, chairman of neurosurgery at the University of Madison-Wisconsin Medical School.

Researchers are also finding other promoters of brain cell growth. Last year, a study showed chemicals known as EGF and FGF improved the ability of mice who suffered strokes to navigate a maze. However, these chemicals must be injected directly into the brain, while prolactin can be injected into the bloodstream.

While it may take years for scientists to unravel the benefits of prolactin, people can safely conduct experiments of their own. "This just shows what sex therapists have known for years," said Marianne White, a Chicago sex therapist and author.

"A healthy sex life makes the brain sharper."

bevenson@nationalpost.com

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