For mice and many other animals, certain behaviors such as mating and fighting are innately programmed, meaning that the animals automatically engage in them when certain stimuli are present. However, there is evidence that under certain circumstances, these behaviors can be overridden. A new study has revealed how illness can affect healthy individuals’ interactions with those who are sick.
Previous studies have shown that mice can distinguish between healthy mice and mice that have been injected with a bacterial component called LPS, which induces mild inflammation when given at a low dose. These studies suggested that mice use odor, processed by their vomeronasal organ, to identify sick individuals.
To explore whether mice would change their innate behavior when exposed to sick animals, the researchers placed male mice in the same cage with either a healthy female or a female that was showing LPS-induced signs of illness.
When studying how otherwise powerful instincts can be overridden in some situations like illness, researchers found that when male mice encountered a female mouse showing signs of illness, the males interacted very little with the females and made no attempts to mate with them as they normally would. The researchers also showed that this behavior is controlled by a circuit in the amygdala, which detects distinctive odors from sick animals and triggers a warning signal to stay away.
Journal reference: Kwon, JT., Ryu, C., Lee, H. et al. An amygdala circuit that suppresses social engagement. Nature (2021). https://doi.org/10.1038/s41586-021-03413-6