UM researcher says receptors in nose and sperm respond to the same scents
A research team led by a scientist now at the University of Maryland School of Medicine has found for the first time that a chemical sensor or receptor that directs human sperm is also present in the olfactory tissue of the nose. The research findings, reported in the October 5, 2004, issue of the journal Current Biology, demonstrate that not only are so-called hOR17-4 receptors found in the nose, they also respond to the same scents as do sperm.
“We detected this protein in the nose using a standard test to determine which proteins are expressed in certain tissue,” says Marc Spehr, Ph.D., a postdoctoral fellow at the University of Maryland School of Medicine. “We found that this nasal receptor responds to and is inhibited by the same odor molecules that excite and inhibit sperm motility. Moreover, our study suggests that in the future, it may be feasible to design compounds that could switch off receptors for unpleasant odors.”
In an earlier sperm study reported last year, the researchers found that hOR17-4 develops its most potent response to a chemical called bourgeonal, which is used by the perfume industry to mimic the lily of the valley scent. Further, they found that another chemical, undecanal, which smells like glue, inhibits the receptor.
To demonstrate the expression of hOR17-4 in the nose, the investigators exposed 488 volunteers (male and female, age 21-37) to various scents, including bourgeonal. The volunteers separated into one experimental group and various control groups. Each group sniffed three odorants presented on paper strips. The experimental group, which included 201 volunteers, was given a strip with bourgeonal for five seconds, followed by a five-second exposure to a strip containing undecanal, followed by another five-second exposure to bourgeonal. Control groups sniffed combinations of undecanal and other scents as well.
“Undecanal strongly inhibited the bourgeonal or lily of the valley odor,” says Dr. Spehr. “But it barely affected the other odors we tested.” There are at least thousands of different odor molecules, according to Dr. Spehr. The study looked at just a handful of scents, but none was inhibited by undecanal to the degree that bourgeonal was. “We think that if hOR17-4 is not the only receptor for lily of the valley detection, then it is at least a very important one.”
Does this protein play a role in sexual attraction? “My gut feeling is I don’t think so,” says Dr. Spehr, “but we don’t have any evidence one way or the other. On the one hand, the same protein is used for fertilization, but in the nose, it is most likely just a regular odorant receptor.”
Dr. Spehr says in mammals, particularly mice or rats, there are more than a thousand olfactory receptors in the nose, but in higher mammals, especially humans, there are only about 350 receptors in the nose that can actually detect smells. The other two-thirds have lost their function, and are known as pseudogenes. He says in the millions of years of evolution between rats and humans, there have been some mutations in the genes for these receptors, so that the genes have stopped functioning.
Dr. Spehr says that in mice hOR17-4 is a pseudogene and does not function. “This may simply suggest that mice detect the lily of the valley scent differently than humans,” says Dr. Spehr. “But this argues for a significant role this receptor might play in any physiological aspect of humans, whatever it is. We assume it might be this fertilization process.”
Dr. Spehr says four of the male volunteers in the experimental arm of the study continued to smell bourgeonal even after exposure to undecanal. He says it may mean that these men do not have the receptor. “If they don’t,” asks Dr. Spehr, “what does this mean in terms of their fertility?”
The studies were performed at the Ruhr-University Bochum, Germany, where Dr. Spehr worked before moving to Baltimore and the University of Maryland School of Medicine earlier this year.
The research was supported by a foundation, the Heinrich and Alma Vogelsang Stiftung.
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