Who suffers from stress? who does not

February 14, 2001

There is an investigator at McGill University in Montreal who has proven with rat litters in the lab what everybody knows in life: loving and caring mothers make for smart rats and children. "The nub of the question," says neurobiologist Michael Meaney, James McGill Professor of Medicine at the McGill Departments of Psychiatry, Neurology and Neurosurgery, "is what determines these differences in maternal behaviours."

Looking for an explanation for the enormous individual differences in how we handle challenges and whether we interpret them as "stressful" (i.e. threatening physically or psychologically), Dr. Meaney chose the rat to see first, how stress affects maternal behavior, and second, how these effects on maternal behavior permanently influence brain and behaviour in the offspring.

Meaney and his team first showed that, as adults, rat pups that received more licking from the mother showed more modest responses to stress. The amount of licking by mothers was determined by the actions in the brain of a hormone called oxytocin. When mothers were themselves stressed, they produced lower amounts of oxytocin and licked their pups less frequently, with the result that their offspring were more reactive to stress in adulthood.

These results are comparable to studies by Jeremy Coplan at Columbia University who showed that irregular supply of food causes rhesus monkey mothers to neglect their infants, resulting in increased emotional reactivity in the offspring. In both the rat and the rhesus monkey, the enhanced reactivity to stress in the offspring is caused by an increase in the activity of the gene that produces a hormone called corticotropin-releasing factor, which triggers stress responses.

Since increased corticotropin-releasing factor is associated with depression and drug addiction, these studies suggest "that the biological pre-dispositions for mental illness could have their origins in early life," concludes Michael Meaney who will speak on "Who suffers from stress and who does not " at the American Association for the Advancement of Sciences (AAAS) on Sunday morning, February 18, in San Francisco.

McGill University

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