June 13, 2006 —Like a man who whips his head around to follow a whiff of perfume, sperm cells turn their heads when they detect even the faintest of sexy female scents, according to a recent study.
The study determined some sperm cells can find ovarian scents even when the scents are diluted 100,000 times. The results were in line with prior research on chemotaxis, the process by which sperm "sniff" sex chemicals and orient themselves in response.
"Sperm have features that are similar to the human nose," said Milos Novotny, who co-led the study and is a professor of chemistry at Indiana University Bloomington.
Sperm cells possess olfactory receptor proteins, Novotny explained, similar to receptors in the nose. They are positioned over the sperm’s membrane, with "sniffers" on the outside and signaling proteins on the inside to relay information.
"Sperm cells must make a decision about where the abundant chemical attractants are at, and then turn toward the site of the action," Novotny told Discovery News. "They have a primitive recognition system, not unlike what some bacteria possess."
Novotny and his team studied mouse sperm using an original device that feeds streams of liquid into a chamber. The researchers introduced sperm into the chamber through one tube, ovarian chemicals in a watery medium through another, and a stream of buffer fluid as a control through a third tube.
As the streams flowed across the chamber, the researchers filmed the sperm in motion. They also collected each of the three streams at the opposite side of the chamber through separate exit tubes.
The researchers found that many of the sperm appeared to detect the chemicals and navigate toward the stream containing them.
The findings were recently published in the journal
Analytical Chemistry.
Although the researchers studied mice, they believe the results likely apply to all mammals.
Prior research found that mammalian sperm are attracted to sex chemicals originating from different mammal species. Researchers are not yet certain what chemicals attract sperm, but they now believe those chemicals are common to all mammals, or at least chemically similar across species.
Novotny and his colleagues are planning additional studies with the flow device. One goal is to identify the female chemicals that have such a powerful effect on sperm.
In a related study published this month in The Proceedings of the National Academy of Sciences,researchers found that sperm virility appears to diminish as men get older.
Brenda Eskenazi, a scientist at the University of California, Berkeley, School of Public Health, and colleagues found that DNA in sperm could increasingly fragment over the years. The researchers previously found that sperm also decline in numbers and become less active as a man ages.
"Our research suggests that men, too, (like women) have a biological time clock— only it is different," Eskenazi said. "Men seem to have a gradual rather than an abrupt change in fertility and in the potential ability to produce viable, healthy offspring."
Since our noses lose some of their detection skills as we get older, it is possible that sperm sensitivity to chemical signals also declines with age.
In the future, the findings may lead to better treatments for male infertility.
