Juvenile Mouse Tears Impact the Brain: How a Pheremone Influences Behavior

Tears aren't just for showing that you're upset. Mice tears apparently secrete a protective pheromone that can impact the brain. It turns out that juvenile mouse tears can actually block adult mating, revealing that chemicals are all-important when it comes to regulating behavior.

In mice, social behaviors are driven by chemical signals, called pheromones. These signals allow mice to interact differently with adults, juveniles and newborns. Until now, though, researchers haven't been sure exactly which sensory cues cause these differences in behavior.

In order to find that out, the scientists decided to examine the genomes of mice to identify the genes that encode pheromones. More specifically, they examined whether pheromone genes were turned on in male and female mice of different ages and physiological states. While scientists knew that sex pheromones made by males influence adult mouse behavior, they weren't sure how the pheromones produced by younger mice influenced behavior.

In the end, the scientists found a molecule called ESP22, which was produced by the tears of juvenile mice. This pheromone, in particular, was an unusual find; juvenile pheromones had not been reported before.

In order to better understand what ESP22 might influence, the researchers traced it to sensory neurons in the vomeronasal organ (VNO), an olfactory structure that humans lack. They found that adult mice that have signaling deficits in this organ displayed increased sexual behavior toward the juvenile mice. In addition, the researchers found that adult mice exhibit the same sexual behavior toward juveniles that don't produce ESP22 but that when the juvenile mice were painted with the chemical, there was a substantial reduction in sexual behavior.

The scientists also decided to track ESP22 in the mice's systems. They found that the molecule activates neurons in the limbic system, an area in the brain that controls instinctive drives. This seemed to show that the chemical influences behavior, though researchers caution that there's still much they don't know.

"We'd love to know what those neurons are, how they compare to other neurons in the limbic system, and how they might mediate responses to other types of pheromones and predator odors," said Stephen Liberles, one of the researchers, in a news release. "We would also like to find the receptor that detects this cue."

The findings reveal a little bit more about how pheromones can influence behavior and brain circuitry. In addition, the research may help scientists examine how chemicals can influence behavior in humans. This, in turn, could allow researchers to better understand how drugs can impact the human brain.

The findings are published in the journal Nature.