- The Washington Times - Thursday, January 2, 2003

CALGARY, Alberta, Jan. 2 (UPI) — An international team of scientists reported Thursday that romance and scent could be more closely linked in the brain than previously thought.

New research shows mice having sex, conceiving their young and giving birth experience hormonal surges that can double the number of new cells in the brain region devoted to smell.

"We're not suggesting that any sort of mating behavior is going to augment brain power," neuroscientist Sam Weiss of the University of Calgary told United Press International. However, he added, investigators plan to experiment with the naturally occurring hormone prolactin as a possible therapy to increase or augment brain cell regeneration "to improve recovery after stroke."

Weiss and colleagues discovered about 10 years ago that adult brains still possess stem cells — the primordial tissues from which all specialized cell types derive. Further studies revealed stem cells create new brain cells, or neurons, that travel to the olfactory bulb, the part of the brain that receives and processes signals from the nose.

In attempts to uncover the growth factors that regulate these brain stem cells, Weiss and his team found genetically modified female mice that possessed fewer new cells in their olfactory bulbs "seemed to be very poor at taking care of their offspring. They just seemed to ignore them," he said.

It was already well known in rodents and many animals that the sense of smell is key to the ability to recognize and take care of young.

"So we asked whether stem cells turn up normal production of these neurons during pregnancy," Weiss said.

By looking at pregnant female mice, Weiss and colleagues at Okayama University in Japan discovered during the first week after conception there was a doubling of new neurons, with another doubling after the mother mice gave birth. This pattern over time perfectly matched prolactin levels in the body during pregnancy. In humans, prolactin stimulates milk production, although it also is found in the nerve tissues of virtually all vertebrates and invertebrates.

In findings appearing in the Jan. 3 issue of the journal Science, the researchers reported female mice that had sex with sterilized males experienced a surge in prolactin and roughly 40 percent more new cells in their olfactory bulbs when compared with females that did not have sex. This suggests conception was not responsible for the change.

Another experiment with genetically modified rodents, whose cells lacked the ability to recognize prolactin, revealed interference with the cell-doubling effect, cementing the notion that prolactin mediates new brain cell production in the olfactory bulb.

The researchers speculate these mating behavior-linked brain changes might help mice and other animals discriminate scents and form new smell-based memories.

Neuroscientist Fred Gage of the Salk Institute in La Jolla, Calif., noted whether or not sex and pregnancy causes brain cell growth in humans remains to be seen.

"The olfactory bulb is an enormous structure in the rodent, and that underlies its relative importance for the survival of the animal. It's not clear how much it persists as a crucial sensory domain for humans," he told UPI.

However, Gage noted pursuing such research in humans certainly "would be an interesting perspective."

Weiss added that, "in humans, the act of mating increases prolactin in circulation both in males and females."

(Reported by Charles Choi, UPI Science News, in New York)


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