By rearing rodent fathers-to-be in stressful conditions, researchers found that they and their subsequent offspring are better able to deal with challenging situations later in life. The findings, published in Nature Communications last month, suggest that very early traumatic experiences can be beneficial—and those benefits may be passed on to the next generation.
Many animal studies have linked early life stress with negative behavioral consequences like increased despair and cognitive deficits in adulthood. People who experience trauma early in life are more likely to be affected by borderline personality disorder or depression. In some cases, however, early moderate stress confers advantages later on, such as resilience to further stress. But can the parent’s susceptibility or resilience to stress-induced psychological disorders be passed on to the offspring?
To determine if beneficial effects are bequeathed, a team led by Isabelle Mansuy from University of Zurich studied the effects of repetitive, unpredictable maternal stress and newborn separation on mice. The team replicated hectic early-life conditions involving neglect and unreliable care by separating male newborns from their mothers, who were subjected to stress at the same time. (The mothers were restrained or forced to swim.) The male pups were then allowed to mature under the care of their stressed parent. When the males grew up and sired their own pups, the team used a range of behavior tests to compare them with control mice raised without stress.
The offspring of stressed-out fathers were more goal oriented and flexible during difficult situations, which allowed them to handle complex tasks more efficiently. “Our results show that environmental factors change behavior and that these changes can be passed on to the next generation,” Mansuy explains in a news release. These are epigenetic changes. Extreme stress, she adds, can affect the brain and behavior across generations negatively, but also in some ways positively.
For example, the offspring of stressed fathers reacted quickly to the changing rules of one test where they were rewarded with a sugary drink. In another test, the mice had to poke their nose into a hole to get water, but only when prompted by a light signal after a pre-determined delay of 6, 12, or 18 seconds. The stressed mice and their offspring performed better at the 18-second interval, which was especially challenging. “Because [the mice] have been put in such traumatic conditions,” Mansuy tells The Scientist, “they develop strategies to be better when their life is somehow threatened.” Although to be clear, the benefits are a very small proportion of the overall effects, she tells Los Angeles Times.
Because the fathers were kept apart from their offspring, the behaviors must have been inherited through a molecular mechanism. The improvements in both stressed fathers and their offspring, they found, were accompanied by changes to the mineralocorticoid receptor gene—which has previously been implicated in stress responses. These changes were due to epigenetic marks that determine how much a gene is expressed, and the altered marks were most likely passed on through the sperm.