Whether conscious of it or not, when entering a new space, we use our sense of smell to assess whether it is safe or a threat. In fact, for much of the animal kingdom, this ability is necessary for survival and reproduction.

“We are trying to understand how animals interact with smell and how that influences their behavior in threatening social and non-social contexts,” says senior author Julian Meeks, principal investigator of the Chemosensation and Social Learning Laboratory at the Del Monte Institute for Neuroscience at the University of Rochester.

“Our recent research gives us valuable tools to use in our future work and connects specific sets of neurons in our olfactory system to the memory of threatening smells.”

SNIFFING OUT THREATS

Smell may guide how the brain responds to a social threat. In mice, the researchers identified a specific set of neurons in the accessory olfactory system that can learn the scent of another mouse that is a potential threat. The research appears in the Journal of Neuroscience.

“We knew that territorial aggression increases in a resident male mouse when it is repeatedly introduced to the same male,” says Kelsey Zuk, first author of the research.

“Previous research has shown this behavior is guided by social smells—our research takes what we know one step further. It identifies where in the olfactory system this is happening. We now know plasticity is happening between the neurons, and the aggression between the male mice may be driven by the memory formed by smell.”

The researchers found that “inhibitory” neurons (nerve cells that act by silencing their synaptic partners) in an area of the brain responsible for interpreting social smells become highly active and change their function when males repeatedly meet and increase their territorial aggression.

By disrupting the neurons associated with neuroplasticity—learning—in the accessory olfactory bulb, the researchers revealed that territorial aggression decreased, linking changes to cellular function in the pheromone-sensing circuity of the brain to changes in behavioral responses to social threats.