Perfume manufacturers would love to find the elusive sex pheromone. This mythical chemical would be so powerful that one whiff would send the opposite sex weak in the knees with reproductive desire.
Exposure to male goat hair can make female goats ovulate, prepping them for mating. Ken Murata and colleagues from the University of Tokyo wanted to find out why smelly goat hair might be responsible for this sexy effect. In results published February 27 in Current Biology, the researchers show that a host of compounds can be found in that billy goat’s ruff. The strongest of these, 4-ethyloctanal, produced pulses in the female goat brain that could promote ovulation. The results may provide clues to pheromones in other species as well.
Goats are smelly creatures with odors in urine, hair and beyond. To isolate potential pheromones in goat hair, the Murata and colleagues constructed a special goat hat containing a material that would absorb volatiles, chemicals that are a vapor at room temperature. While there are no photos of this ingenious piece of headgear, analysis of the compounds absorbed by it showed that male goats exude a complex cocktail of chemicals from the head, chemicals that castrated male goats can’t make.
The scientists then took female goats and measured the electrical signals in their brains associated with firing neurons. They were specifically looking at the arcuate nucleus of the hypothalamus, an area that releases hormones like gonadotropin-releasing hormone, or GnRH. GnRH signals the release of luteinizing hormone – which in turn plays a role in making female goats (and humans) ovulate.
When female goats sniffed the sweet pheromones of the male, Murata and colleagues showed that rhythmic spiking of GnRH signals in the goats’ brains increased, becoming faster and larger. As spiking of GnRH pulses increases, luteinizing hormone release could increase as well. This would mean that a whiff of that manly goat smell makes lady goats ready to roll in the hay.
Stephen Liberles, a cell biologist at Harvard University, says that the results are important for the field of pheromone response. “[Murata and colleagues] can record directly from neurons in the brain and a see a response to a particular pheromone in the periphery,” he says. “No one’s done that experiment before and it’s very exciting.” But Liberles notes that because the study was performed in female goats with their ovaries removed (which is a way to make sure they are not already in rut), the researchers were unable to confirm whether exposure to 4-ehtyloctanal actually caused ovulation. “The next step,” Liberles says, “would be to see if it actually affected the reproductive state directly.”
Jeremy Smith, a neuroendocrinologist at the University of Western Australia in Nedlands, is hopeful that the identification of one pheromone in goats will pave the way for identification of pheromones in other species. “If we know the basic chemical structure in goats,” he says, “then we can search for, and test, similar compounds in sheep and cows.”
Finding active pheromones that make female animals fertile could be very important for the way humans current raise livestock. For example, female sheep receive hormone treatment to make sure they are in rut for breeding. “Using pheromones,” Smith explains, “would be a cheaper, less invasive and cleaner (no hormone treatment) practice.”
And of course, perfume companies are still searching for that elusive human pheromone. Finding a pheromone in goats does not mean scientists will find one in humans, but if they were to go hunting, knowing what kind of chemical to look for is an important clue. A human pheromone could be more than just a dating aid. Smith says that some sort of treatment with human pheromones, if they are found, could potentially “increase fertility without the need for invasive hormone treatments.” But, he notes, “I’d imagine perfume companies would be interested as well.”
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