Researchers accidentally discover why male mice are afraid of bananas

Researchers accidentally discover why male mice are afraid of bananas

By studying the reaction of male mice to pregnant and lactating female mice, researchers made a related and somewhat odd discovery: Male mice are terrified of the smell of bananas.

A team from McGill University in Montreal, Que., was looking at spikes in stress hormonal responses in male mice in close proximity to late-pregnant female mice.

“Male mice display stress and are stress-induced [pain inhibition] in close proximity to late-pregnant or lactating female mice,” the team wrote in their report, published in Science Advances. foreign male mice with intact gonads with aggression and urinary marking. »

Male mice are well known to be aggressive and infanticidal towards pups, in order to protect their own genetics. The heavily pregnant and lactating mice—in addition to aggressively defending their babies—emit chemicals to warn these males to move away.

“Rodents and many mammals other than humans rely on their olfactory senses,” the study’s lead author, Professor Jeffrey Mogil, told Live Science. “Urine scent marking is well known, but what we found here is a new message that has never been described before in mammals.

“We have seen a lot of olfactory messages sent from men to women, but there are fewer examples of women sending them to men. Most of these messages have to do with sexual behavior, but in this case sex has nothing to do with females telling males to stay away or else be prepared for me to beat the crap out of you if you touch my puppies.

So where do bananas come from? Do they also issue a warning to male mice? Coincidentally, yes, but not to protect their own pups. The authors found that the compound n-pentyl acetate – found in the urine of female mice, especially during pregnancy and lactation – was one of the chemicals with the greatest effect on hormonal changes in male mice.

“n-Pentyl acetate,” the team explains in the study, “is very similar in chemical structure to isoamyl (or isopentyl) acetate, and both are found in a variety of fruits and are used to produce banana oil/extract”.

The team bought banana oil extract from the supermarket and placed it inside the cages of male mice to measure their stress levels, which increased dramatically in response. The team believe the stress response in mice is similar to the stress response when they are about to engage in a fight.

“Although maternal attack is not always successful in preventing male intruders from committing infanticide, any threat of violence is likely to produce stress in both parties, and maternal aggression has been shown to directly produce intruders induced by stress. [pain inhibition] in men measured after attacks,” the team wrote in their study.

“What we are currently demonstrating is that stress induces [pain inhibition] in male mice can be observed even in the absence of actual maternal aggression; the mere threat of such aggression is sufficient and that this threat is communicated via volatile urinary compounds.”

The study found that virgin male mice were more likely to be stressed by the presence of n-pentyl acetate, whether in the form of banana or mouse pee. This is consistent with their tendency to be more aggressive towards infants than non-virgin mice, suggesting that they pose more of a threat to infants than older males.

“The current results suggest that the proximity of male subjects to reproductively active females is a previously unknown stressor for males,” the team concluded, “and that stress may even be caused by the proximity of certain foodstuffs”.

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