Mice Have A Brain Circuit Preventing Them From Choosing Sick Mates

Neuroscientists at MIT have identified a circuit in the brain of mice that prevents the mice from mating with mice that are sick. Researchers in the study explored how the powerful instincts could be overridden in some cases. The scientists say that when male mice encounter a female mouse showing signs of illness, the male mice interacted very little with the female and made no attempts to mate as they normally would.Researchers found behaviors controlled by a circuit in the amygdala able to detect odors emanating from sick animals and triggering a warning to stay away. In the animal community, it's essential for creatures to be able to distance themselves from sick individuals. This is particularly important and species like the mouse, where mating is driven by instinct. Researchers say in these creatures, it's imperative to have a mechanism able to shut down instinct when the risk is high.

In mice and other animals, behavior like mating and fighting are programmed innately, leading the animals to automatically engage in them if certain stimuli are present. Evidence now shows that under certain circumstances, the behaviors can be overridden. In past studies, researchers have shown that mice can distinguish between healthy mice and mice injected with a bacterial component called LPS, inducing mild inflammation.

The study suggested mice use odor processes to identify sick creatures. Researchers identified the brain circuit that controls that behavior; it's called the vomeronasal organ. That is the same organ that processes pheromones and feeds into the amygdala component called COApm. That region is activated by the presence of LPS-injected animals.

Additional experiments found that activity in COApm is necessary to suppress the mating behavior in males in the presence of ill female mice. If COApm activity was turned off, the males would try to mate with sick females. Stimulating COApm artificially in male mice suppresses the mating behavior even when they were around healthy females.