Brain Circuit Stops Mice From Mating With Sick Individuals

To help prevent the spread of COVID-19, many people around the world have been practicing social distancing, physical distancing — staying at home, avoiding dinner dates at all cost, and keeping a distance from others when you're out and about. Scientists had previously discovered that vampire bats also partake in the practice, and turns out, mice are in the social distancing club, too.

Researchers from Massachusetts Institute of Technology's Picower Institute for Learning and Memory found that male mice avoid female mouse showing signs of illness, according to a press release by the university.

"As a community, it’s very important for animals to be able to socially distance themselves from sick individuals," said Gloria Choi, an associate professor of brain and cognitive sciences at MIT and a member of the Picower Institute. "Especially in species like mice, where mating is instinctively driven, it’s imperative to be able to have a mechanism that can shut it down when the risk is high."

The study, which was published in Nature, looks at how mice's innately programmed behavior such as fighting and mating is affected when certain stimuli are present. "We wanted to see whether there's a brain mechanism that would be engaged when an animal encounters a sick member of the same species that would modulate these innate, automatic social behaviors," Choi said.

Sickness and avoidance to mate

In order to conduct the experiment, male mice were placed in the same cage with either a healthy female or a female that was showing signs of illness. Previous studies had suggested that mice use odor to identify infected individuals, and as a result, scientists saw that males engaged much less with the sick females and made no effort to mate with them.

The researchers also identified the brain circuit behind this social distancing behavior. They state that the mice's behavior is controlled by a circuit, called the COApm, in the amygdala, which detects the specific odors from sick animals and triggers a warning signal to stay away. When COApm activity was turned off, males tried to mate with sick females, which suggests its presence is crucial to suppress mating behavior.

Another interesting outcome of the study was that the fact that the COApm communicates with another part of the amygdala called the medial amygdala. The communication between the two takes place thanks to a hormone called thyrotropin-releasing hormone (TRH). This is crucial to suppressing mating behavior, and this link is intriguing, according to Choi.

Thyroid dysfunction has been connected to depression and social withdrawal in humans, and further exploration of this could yield interesting findings.

“This is something we are trying to probe in the future: whether there's a link between thyroid dysfunction and modulation of this amygdala circuit that controls social behavior,” Choi says.