The finding came as the researchers were analyzing the spikes in stress hormones that occurred in male mice when they approached pregnant or lactating females. They discovered that these hormonal changes were triggered by the presence of a compound called n-pentyl acetate, which, surprisingly, gives the banana its characteristic smell.
“This was all a surprise, as we weren’t looking for this in particular and found it by accident,” Jeffrey Mogil, the study’s lead author, told Live Science . “The pregnant females were in our lab for another experiment, and one of our graduate students noticed that the males were starting to act strange.”
In the paper, which has been published in Science Advances , the researchers wrote that “male mice, especially virgin males, are well known to engage in infanticidal aggression to advance their genetic fitness.” To prevent this behavior, pregnant and lactating females emit chemicals through their bodies to tell males to stay away from their young.
“Mice can discriminate conspecifics and their characteristics through urine odor cues and use those cues for signaling purposes. There are many well-studied examples of chemical signaling between males and females in adults that affect reproduction and other behaviors; far fewer examples of signaling between females and males have been documented in rodents. There is also a relative paucity of examples of intersex chemosignalling unrelated to sexual behavior (ie, reproductive physiology and social attraction). In an intriguing example, a recent study described the ability of tear fluid from female mice to inhibit aggressive behavior in males,” the researchers write in the publication.
Jeffrey Mogil, lead author of the study, and his team saw how the males’ stress level increased in response to chemicals in the females’ urine, specifically n-pentyl acetate. The researchers wondered if the animals would react the same to n-pentyl acetate from a different source. To do this, they bought banana oil and soaked cotton balls in it. They put the balls in the cages of the male mice and observed what happened. What happened was that, in the presence of the odour, stress levels increased appreciably, just as had happened with the females’ urine. The researchers suspect that this hormonal surge is directly related to the stress we feel in the face of a possible fight .
The study authors reported the analgesic effect of urine or plantain oil exposure in that males had less sensitivity to pain. Pain resistance developed very rapidly, arising as soon as five minutes after smelling n-pentyl acetate and diminishing 60 minutes after smelling it. They also found that levels of stress-induced analgesia were significantly higher in virgin males, suggesting that they pose a greater threat to the offspring than the parents themselves.
The findings make us reflect on the invisible communication channels that animals use to talk to each other and how this communication can be richer than we think.
Referencia: Mogil. J. et al. 2022. Olfactory exposure to late-pregnant and lactating mice causes stress-induced analgesia in male mice. Science Advances. DOI: 10.1126/sciadv.abi9366