Animals Use Pheromones to Communicate, but Do Humans?

Aug. 28, 2000 -- Some couples just seem to have a certain chemistry together. Research is showing that they might be exactly right.

Scientists now believe they have found the first human gene associated with the function of pheromones, odorless molecules wafting through the air that signal key survival responses in animals, like dealing with danger or finding a mate.

While rodents and other creatures essentially are reactive animals that depend heavily on pheromones for behavioral cues, it has been a topic of debate whether humans kept any pheromone function along the course of evolution. Humans use their larger brains to rely more on judgment and complex sensory cues, such as vision.

Researchers studying animals have shown how pheromones work, tracing complex neurological paths to stimulate parts of the brain that are deeply rooted in instinct.

Scientists have had their suspicions that humans also use pheromones to communicate with each other chemically. But only recently have experts been able to tease out the parts of the human body that might function this way.

Neurogeneticists at Rockefeller University and Yale say they have isolated a human gene, labeled V1RL1, they believe makes a pheromone receptor, or the chemical's personal reserved parking place. Pheromones would attach to this receptor when they are inhaled into the mucous lining in the nose.

"This is the first convincing identification of a human pheromone receptor," said University of Colorado biochemist Joseph Falke, PhD.

Rodents and other mammals also have the V1RL1 gene, and they rely heavily on pheromone cues to survive. However, it has not been determined whether the gene is active in humans or what sort of activity the gene could trigger.

"The ultimate test will be to find a pheromone that binds to the receptor and triggers a measurable physiological response," Falke said.

The research was published in the September issue of the journal Nature Genetics.

Researchers took samples from a gene bank and scanned them for matches to the rodent genes from the V1r family. They found eight matches in human genetic material.

Further testing showed that seven of the eight human V1r genes are inoperative. The potentially functional gene, V1RL1, subsequently was found in 11 out of 11 randomly chosen people from varying ethnic backgrounds, researchers said.

"In mice, we think there are more than 100 functioning genes in the V1r family," said Ivan Rodriguez, PhD, of Rockefeller University, lead author of the study. "But in humans, V1RL1 may very well be the sole functioning gene in the family."

"Why has it hung around all this time?" said Charles Wysocki, MS, PhD, of the Monell Chemical Senses Center in Philadelphia. "It must be very important if it has outlived all of its predecessors."

Scientists aren't sure what happened to the other 99 genes.

"It's unheard of that a family of 100 genes in mice is reduced to a single gene in humans," said the study's senior author, Peter Mombaerts, MD, PhD.

In most mammals, pheromones usually are detected by a specialized organ inside the nose or mouth called the vomeronasal organ, or VNO. Nerves connect it to parts of the brain involved in reactions rather than cognition.

In humans, the organ appears in embryos with its nerve cells extending into the developing brain. For several weeks, it serves as a pathway for hormones vital to sexual development and maturity. However, most experts believe that the VNO in humans shrinks and stops working before birth.

In April, however, researchers in Utah reported that they found a pheromone that seemed to help reduce nervousness, tension, and other stress in women. The report, which was published in the journal Psychoneuroendocrinology, announced that the chemical worked through the VNO pathway.

"We definitely found that human beings communicate with each other with pheromones, just like any terrestrial animal," study co-author David L. Berliner, MD, told WebMD in April. "And they do it through the same organ that all these terrestrial animals have, which is a vomeronasal organ, which all human beings have."

Berliner and his team reported that a metabolic product of testosterone, called androstadienone, could trigger the VNO when the molecule was introduced to participants through a tiny tube. Androstadienone is found on the surface of body hair and skin in men.

Berliner, president and CEO of Pherin Pharmaceuticals, told WebMD that androstadienone doesn't trigger sexual responses, so love potions may not be in the near future with this molecule. But other products are possible, such as those that use the VNO to soothe anxiety attacks and premenstrual syndrome.

Several studies have linked pheromones to a woman's reproductive system. In 1998, a study at the University of Chicago demonstrated that pheromones in underarm sweat prompt women living in close quarters to synchronize their menstrual cycles.

Some companies put pheromones in perfumes. Chemical makers bait insect traps with pheromones.

Mombaerts said it is too early to tell whether the gene discovery might lead to pheromone-based medicines.

However, the potential for pheromone misuse worries some researchers and bioethicists.

"Safeguards will be needed to prevent the manipulation of human behavior," Falke said. "We won't want pheromones showing up in magazine ads or pumped through ventilation systems at the mall."