When they have pups to protect, normally timid female mice will ferociously attack male mice. This radical change in behaviour is because nursing mothers have low levels of a brain hormone associated with fear and anxiety.
Corticotropin-releasing hormone (CRH) is released in stressful situations. Lactating animals, including humans, have low levels of CRH in the brain, which is thought to make them calmer. Stephen Gammie and colleagues at the University of Wisconsin in Madison wondered if the low levels of CRH in nursing animals might also be responsible for their famed bravery.
The team injected three different concentrations of CRH…
