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Research provides evidence of air-borne pheromones (Released: 10/22/96)

by David Pesci, Office of University Communications.

STORRS, Conn. -- Females are much more attractive if males stand downwind -- that is, if the males and females are rats.

These are the findings from new research by Benjamin D. Sachs, a professor of psychology at the University of Connecticut. Through a variety of controlled tests, Sachs discovered that female rats apparently emit an airborne "social odor," or pheromone, that acts as an aphrodisiac for male rats. The odor is so effective that it causes erections in the male rats encountering it.

Why is this significant? We often speak of chemical attractions, or of one person being attracted to another from across a crowded room. But scientists have little understanding how such reactions work. It is well known that males of many vertebrate and invertebrate species are attracted to sexual scents and will approach them. However, this is the first study that has produced evidence of a female pheromone producing physical arousal in a male mammal from a distance.

"There are no other studies out there that show this type of reaction being triggered in a mammal by volatile scent alone," Sachs says.

The study is also important because until now, it was widely believed that all but a few animal species needed physical contact to produce erections. Non-contact or "psychogenic erections" are produced at a distance through sensations of vision, sound or smell, but have only been observed in humans, horses, some types of antelopes, and a few non-human primates such as chimpanzees and rhesus monkeys. The addition of rats to the list should promote further research on the physiology of this response.

It is also interesting to note that the arousing odor came from female rats, Sachs says, because perfumes and colognes that include scents such as musk that are attractive to humans of both sexes use scent extracts derived from male animals.

Sachs' study used 40 virgin male rats. They were placed in chambers that were either upwind or downwind from sexually receptive female rats. For the purpose of the experiments, receptivity was induced in the female rats by injecting them with hormones. Of the 20 males downwind from the females, 11 experienced erections. However, when the same rats were placed in a chamber upwind of the females, only one of the males became physically aroused.

Control tests also were conducted where half the males could see and hear the females while the other half could not, but the response of the male rats did not change. The deciding factor was the ability to perceive the females' scent. The males also were tested again after mating twice with the same results, suggesting that sexual experience was not essential for the response to occur.

Finally, half the males were tested a few weeks later with the females anesthetized so that they could not make sounds. Half of these females were sexually receptive. Six out of 10 of the males responded with erections to the receptive females, while only one of the males responded to the unreceptive females.

Together, the experiments show that the deciding factor in the male's sexual response was his ability to perceive the female's scent rather than seeing or hearing her.

Sachs has been studying brain mechanisms involved with this response for several years. He also hopes to study whether some females produce more effective pheromones than other females, and whether male rats respond only to pheromones of their own species.

"Scientists have been studying the physiology of mating behavior in rats for 70 years," Sachs says. "They have observed rats in similar situations during many of these studies but not noted the response. It shows we have much to learn about the behavioral repertoire of rats and other species and also about the underlying physiological mechanisms of these behaviors."

Sachs will present his findings at the annual Society for Neuro-Science conference in Washington, D.C., November 16-21.