A rodent mother can't scold or praise her offspring, but her approach to mothering lays a genetic foundation for her pups' lifelong response to threats, neuroscientists have found.
Rats raised by moms who frequently lick and groom them undergo permanent changes in patterns of gene activity, leading to a penchant for exploratory behavior in stressful situations, say Michael J. Meaney and his colleagues at McGill University in Montreal.
In contrast, rats raised with little maternal contact end up with gene activity that fosters fearfulness in the face of stress, the researchers report in the August Nature Neuroscience. From an evolutionary perspective, having both behaviors in a population is beneficial.
"Early experience can have lifelong consequences on behavior, and [this new report] reveals the genetic scaffolding of this phenomenon to an unprecedented extent," remarks neuroscientist Robert Sapolsky of Stanford University.
Meaney's group previously showed that female rats express either a high- or a low-contact mothering style. Animals raised with lots of physical contact later react to stress by secreting small amounts of glucocorticoids, a class of stress hormones. These rats also possess large numbers of glucocorticoid receptors in an inner-brain structure called the hippocampus. Rats raised with little physical contact secrete large amounts of glucocorticoids when stressed and possess relatively few receptors for these hormones.
In another study, Meaney's group found that pups raised by doting mothers had high concentrations of a …