Researchers at the University of Calgary in Alberta have shown that female mice tend to create new brain cells when they detect a dominant male's urine, a discovery that outlines how chemical messages may shape their choice of mates.
Dr. Samuel Weiss and his colleagues at the university looked at the effects of sex pheromones, chemicals in urine that many animals use to recognize and choose their mates, on the brains of female mice. They housed the animals with soiled litter for a week.
The researchers observed that mice exposed to urine from dominant males showed around a 25 per cent in crease in new neurons in two brain regions-hippocampus and the olfactory bulb, involved in learning and memory and smell respectively. Mice exposed to clean bedding or urine from females or subordinate males did not show any such increase in the brain cells.
"Adult neurogenesis may be involved in female mate selection," Nature Neuroscience quotes Weiss as saying.
"Seeing an increase in both areas at once was surprising, but then mate selection is an intrinsically important behaviour," he adds.
The researchers believe the pheromones bind to specialized receptor proteins, which then signal to another brain region called the hypothalamus, triggering the release of hormones that cause the birth of new neurons.
"This mechanism is likely to be just one piece of the puzzle," says Barry Keverne of the University of Cambridge, who has shown that male mouse urine can also trigger the production of new neurons inside a female's vomeronasal organ, a sense organ thought to aid pheromone detection in some mammals.
Although humans have receptors similar to those found in mice, the researchers are not sure whether pheromones trigger neuron formation in humans or not. They say that it is still a matter of speculation whether a subconscious whiff of an alpha-male's urine could turn a woman's head.
"Olfaction is a subtle and underappreciated sense. Maybe we've underestimated its importance," says Weiss.