If you've always suspected that your childhood warped your brain, now you might have a stronger case. New research reveals how different nurturing styles by mother rats influence the brains of their pups, leading to very differently natured offspring.
Being taken away from mom for a few minutes is a stressful ordeal for baby rats. But whether they're scarred for life depends entirely on how mom reacts when the family is reunited. Pups who are showered with affection upon return grow up to be well-adjusted adults--less fearful and stressed than peers greeted with a lukewarm response. Research has suggested that these behavioral differences result from lifelong changes in the hippocampus, a brain region that helps regulate the body's response to stress.
To investigate these changes, a team of scientists led by Michael Meaney of McGill University in Montreal, Canada, investigated DNA from rats they'd separated from their mothers and then reunited. They found that right after birth, cells attach a chemical tag to a stretch of DNA that encodes a particular receptor for glucocorticoid hormones in the brain. These hormones mediate the body's response to stress. The tag usually keeps the receptor gene turned off, but in rats lavished with motherly love, the tag gets removed and more receptors are made, the researchers report in the August issue of Nature Neuroscience. The researchers speculate that the additional receptors change the brain's sensitivity to stress hormones in a way that dampens anxiety. The scientists also found that extra loving from mom changed the way cells package this DNA, making it easier for cells to turn on the receptor gene.
By describing the sequence of steps that link mom's behavior to changes in a rat pup's brain, the team has made an impressive contribution, says Bruce McEwen of Rockefeller University in New York City: "The work will have a lot of impact."
In the same issue, Elizabeth Gould and colleagues at Princeton University report further evidence of the power of parenting. They also separated young rats from their mothers, and once the rats grew up, looked at nerve cell growth in their brains. The adult rats that were deprived of mom as children didn't grow as many new cells in their hippocampuses. And when exposed to the smell of foxes, usually a stress-inducing event, the rats' brains didn't react the way a normal rat brain does. Gould's team speculates that childhood stress makes the brain less plastic, diminishing its ability to respond to stress as an adult.
Together, the studies suggest that the nature-versus-nurture question may soon be moot, says Moshe Szyf of the McGill team. "We have bridged the gap," he says. "Nurture is nature."