Neuroscientists at MIT have identified a circuit in the rat brain that prevents mice from mating with sick mice. The study’s researchers explored how powerful instincts can be overridden in some cases. Scientists say that when male rats encounter a female that shows signs of disease, the male rats interacted very little with the female and made no attempt to mate as they normally would.
The researchers found behaviors controlled by a circuit in the amygdala capable of detecting odors emanating from sick animals and triggering a warning to stay away. In the animal community, it is essential that creatures are able to distance themselves from sick individuals. This is particularly important for species like the mouse, where mating is driven by instinct. The researchers say that in these creatures it is imperative to have a mechanism capable of turning off the instinct when the risk is high.
In rats and other animals, behaviors such as mating and fighting are innately programmed, causing animals to automatically engage in them if certain stimuli are present. The evidence now shows that, in certain circumstances, behaviors can be replaced. In previous 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 that rats use odor processes to identify sick creatures. The researchers identified the brain circuit that controls this behavior; it is called the vomeronasal organ. This is the same organ that processes pheromones and feeds the amygdala component called COApm. This region is activated by the presence of animals injected with LPS.
Additional experiments have found that activity in COApm is necessary to suppress mating behavior in males in the presence of sick female mice. If COApm activity were turned off, males would try to mate with sick females. Stimulating COApm artificially in male mice suppresses mating behavior, even when they were close to healthy females.