Wow (link):
"We separated the pups from their mothers for three hours each day for ten days," Dr Murgatroyd explained.

"It was a very mild stress and the animals were not affected at a nutritional level, but they would [have felt] abandoned."

The team found that mice that had been "abandoned" during their early lives were then less able to cope with stressful situations throughout their lives.

The stressed mice also had poorer memories.

Dr Murgatroyd explained that these effects were caused by "epigenetic changes", where the early stressful experience actually changed the DNA of some of the animals' genes.

"This is a two-step mechanism," Dr Murgatroyd explained.

When the baby mice were stressed, they produced high levels of stress hormones.

These hormones "tweak" the DNA of a gene that codes for a specific stress hormone - vasopressin.

"This leaves a permanent mark at the vasopressin gene," said Dr Murgatroyd. "It is then programmed to produce high levels [of the hormone] later on in life."

The researchers were able to show that vasopressin was behind the behavioural and memory problems. When the adult mice were given a drug that blocked the effects of the hormone, their behaviour returned to normal.