Sep 22: When mice heard a sound they thought signaled danger, they moved closer to a familiar companion, according to Virginia Tech researchers.
They did not do the same when paired with a mouse they didn’t know.
The study, led by Alexei Morozov of the Fralin Biomedical Research Institute at VTC and published in the September issue of Neuropsychopharmacology, begins to reveal how the brain turns a warning signal into a drive to seek familiar company.
Scientists have long observed that animals gather when confronted with immediate threats such as predators. The new study asked whether a learned warning signal could produce a similar response and, if so, which biological mechanisms might be involved.
Researchers first trained mice individually to associate a tone with a short, mild foot shock. One to two days later, they placed the mice in pairs and played the tone again. Mice that had previously lived together drew closer when the tone played, while those paired with strangers showed no consistent change in distance.
The tendency to draw closer was not linked to freezing, a common response to fear in which mice remain still. This suggests that seeking a companion and freezing are distinct responses to the same warning signal.
The researchers did not observe overt comforting behaviors such as grooming or huddling. Instead, they measured a decrease in the distance between the animals’ snouts, indicating that the familiar mice drew closer and oriented toward one another.
“Mice are territorial, so an unfamiliar mouse of the same sex may seem more like a threat than a source of safety,” Morozov said. “Something similar can happen among people, who may be less inclined to cooperate with groups they don’t know. Learning about one another can help break down that barrier and make it easier to face shared dangers together.”
The team then temporarily suppressed neuronal communication from the basolateral amygdala in the mouse brain, which helps process threatening cues, to the ventral hippocampus, a region involved in social memory. Disrupting that pathway prevented the mice from moving closer when they heard the tone, without changing how much they froze.
In addition, blocking receptors for oxytocin — a chemical messenger involved in social recognition and behavior — also prevented the overall proximity response. Researchers have not yet determined where exactly in the brain it acts to influence this particular response.
“Our findings suggest that the amygdala, which recognizes threats, recruits the hippocampus to coordinate a social response to danger,” Morozov said. “However, the hippocampus, which stores social memories, also acts as a gatekeeper, allowing that coordination only between familiar animals. Studying hippocampal activity will help uncover how that gate works.”
“This work is providing insights into the precise brain circuits and biological processes that mediate these important social behaviors,” said Michael Friedlander, Virginia Tech’s vice president for health sciences and technology and the executive director of the Fralin Biomedical Research Institute. “These creative experiments by Dr. Morozov and his team represent much more than just exploring a basic mechanism — they also begin to provide the level of mechanistic understanding that will be essential to develop precise therapies to address neuropsychiatric disorders in which adaptive social interactions in humans are compromised.”
The study was conducted by Wataru Ito and Morozov of the Fralin Biomedical Research Institute. Morozov is a faculty member of the institute’s Center for Neurobiology Research and also holds an appointment in the Department of Psychiatry and Behavioral Medicine at the Virginia Tech Carilion School of Medicine.
The research was supported by the National Institutes of Health and the Seale Innovation Fund.