Scientists turn on predatory kill instinct in mice

Brain circuits that turn a normal mouse into a vicious hunter have been found tucked away in the brain, with one set of cells responsible for prey pursuit and the other for killing it.

Wenfei Han from Yale University and colleagues from the US, China and Brazil activated the areas, found in the part of the brain associated with fear and emotion called the amygdala, in the brain of lab mice.

The animals were transformed into hunting machines, chasing never-seen-before prey and biting everything in their path, even sticks and bottle caps. The work was published in Cell.

“This area, the central amygdala, seems to allow the animal precise control over the muscles involved in pursuing and capturing prey,” explains Ivan de Araujo, senior author of the paper.

Previous work has shown that hunting activates cells in the rat amygdala. Might it work in the opposite direction – could triggering those brain circuits lead to hunting behaviours?

To find out, the researchers used techniques called chemogenetics and optogenetics in mice. Brain cells were genetically engineered to fire if laser light of a certain colour was shone on them or they were exposed to a certain drug.

And upon activation with a fibre optic light source or injected drug, normal lab mice were transformed into fierce super-hunters, preying on just about any inanimate object that fell in their path.

“We’d turn the laser on and they’d jump on an object, hold it with their paws and intensively bite it as if they were trying to capture and kill it,” de Araujo says.

Interestingly, the mice didn’t attack each other, and hungry mice responded more vigorously than those with a full belly.

“The system is not just generalised aggression,” de Araujo explains. “It seems to be related to the animal’s interest in obtaining food.”

By separately triggering and deactivating the neurons in question, the researchers deduced that one set controlled the animal’s prey instinct, helping to home in on its target, while another controlled the muscles in its jaw and neck, producing the actions required to bite and kill.

Without the latter set, de Araujo says, the mice pursued their prey but failed to “deliver the killing bite”.

De Araujo is now interested to investigate how the two sets of neurons communicate to combine their output. “We now have a grip on their anatomical identities, so we hope we can manipulate them even more precisely in the future.”