Aware 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 essential for survival and reproduction. Researchers at the Del Monte Institute of Neuroscience at the University of Rochester are finding new clues as to how the olfactory sensory system helps assess threat and have found neurons that “learn” if an odor is a threat.
“We’re trying to understand how animals react to smell and how that affects their behavior in threatening social and non-social contexts,” said Julian Meeks, PhD, principal investigator in the Chemical Sensitization and Social Learning Laboratory. “Our latest research gives us valuable tools to use in our future work and connects specific groups of neurons in our olfactory system to memory of threatened odors.”
Learn to smell a threat
How the brain responds to a social threat can be directed by smell. In mice, the researchers identified a specific group of neurons in the accessory olfactory system that can recognize the scent of another mouse that is a potential threat. These findings are described in a paper recently published in Journal of Neuroscience.
“We knew that territorial aggression is increased in a resident male mouse when it is presented repeatedly to the same male,” said Dr. Kelsey Zook, who was the first author of this research. “Previous research has shown that this behavior is guided by social odors – our research takes what we know a step further. It pinpoints where in the olfactory system this occurs. We now know that plasticity occurs between neurons, and aggression between male mice may be driven by a memory shaped by an odor.” “.
The researchers found that “inhibitory” neurons (neurons that work by silencing their synaptic partners) in a region of the brain responsible for interpreting social odors become hyperactive and alter their function when males meet frequently and increase their territorial aggression. By disrupting neurons associated with neuroplasticity — learning — in the accessory olfactory bulb, the researchers revealed that territorial aggression decreased, linking changes in cellular function in the brain’s pheromone-sensing circuit to changes in behavioral responses to social threats.
“It canceled out the heightened aggression that would normally be displayed,” Zook said. “It suggests that this group of early sensory neurons plays an important role in regulating the behavioral response to social odors.”
Meeks was the lead author on this paper. Additional authors include Jinxin Wang, PhD, of the University of Rochester Medical Center and Hilary Kansler, PhD, University of Florida School of Medicine. The research was supported by the National Institutes of Health.
A new menacing scent
Threat assessment also comes when an animal is tripped by an unknown scent. For example, the smell of an unprecedented predator. Researchers in the Chemical Sensitization and Social Learning Laboratory found that the scent of a new predator, such as the scent of a snake to a mouse, caused the animal to engage in threat assessment behavior — acting neither “frightened” nor “safe.”
said Jinxin Wang, Ph.D., and first author of a paper in eNeuro. “Identifying changes in the animals’ behavior patterns helps us better understand how threatening odors are processed in the brain.”
The researchers used video tracking to monitor the movement and posture of mice exploring familiar environments with different scents – such as rats and other snakes. Wang and his colleagues developed a hybrid machine-learning approach that helped them detect how mice respond to predatory odors in ways that are unique and distinct from how mice react to non-predator odors. These behaviors were neither frightening nor safe but rather an evaluation case.
“These findings provide new evidence about how odors influence social behavior and what they may mean for survival, but this study also provides new tools that will move this science forward,” said Meeks, senior author of this study. “We combined methods with known limitations to improve the accuracy, depth of information, and human interpretability of the data collected. We believe that this approach will be valuable for future research on how the mixture of chemical odors emitted by predators triggers threat assessment in the brain.”
Additional authors include Baniz Karbasi, PhD, and Liqiang Wang, PhD, of the University of Texas Southwestern Medical Center. The research was supported by the National Institute on Deafness and Other Communication Disorders.