Give Michael Meaney, PhD, of the Douglas Hospital Research Centre five years and he may be able to tell us how to better prepare our children for some of the future challenges they may face. The studies he has conducted on laboratory rats to date already have revealed much in this respect. Specifically, they have shown that a mother’s touch may not only be a comforting and pleasant experience for her child, but may also be a means by which genes involved in shaping our response to stress get turned on or off.

Michael Meaney explains that the possible rat equivalent to a human mother’s touch is licking. Much like in humans, different “parenting styles” exist among rats, such that some rat mothers lick their pups more than others. He has shown that, when exposed to stress, the offspring of high-licking mothers produce lower levels of stress hormones, including glucocorticoids.

The stress hormones are released to help the body deal with a threat or a stressor. In the short-term, this rise in glucocorticoids is adaptive; however, repeated or long-term use of this stress-response system can have detrimental effects and has been linked to heart disease, diabetes, immune dysfunctions, and mental illness. Moreover, while glucocorticoids help to ensure the adequate function of a brain structure (called the hippocampus), which is involved in learning and memory, excess glucocorticoids have been linked to damage of the hippocampus and to poor memory. Thus, there are clear advantages in having a high-licking mother. Under certain conditions, the pups reared by high-licking mothers are calmer during stress, and show a greater capacity to learn, relative to pups reared by low-licking mothers.

It appears that the stimulation provided by licking produces changes in the function of genes in the pups’ brains. While a pup is in the womb, genes that help guide the normal development of the brain and body are turned on and off through a variety of processes. When a rat mother licks her pups, she turns on the gene involved in reducing the amount of glucocorticoids they will release in the face of stress.

From Rats to Humans

How does this translate to humans? Over the next five years, Michael Meaney and his colleagues from across the country will examine whether aspects of parental care, such as touch, have the same effects on the DNA of human babies. This $4 million study, called the MAVAN project (Maternal Adversity Vulnerability and Neurodevelopment) and supported by the Canadian Institutes of Health Research, should provide invaluable data on the effects of parental care on child development.

There are, of course, differences in parental care in humans. Mothers with severe depression for instance, can have difficulties bonding with their children, and tend to touch and caress their babies less than others. Michael Meaney and his group will therefore follow a group of depressed mothers throughout pregnancy and, for the next four years, will compare them to a control group of mothers without depression.

Although all of the depressed women will be offered treatment, past research indicates that a third of them may not respond. Interestingly, Michael Meaney has shown that, when a rat mother is exposed to stress during pregnancy, she tends to lick her pups less. In humans, being depressed during pregnancy can be considered a form of stress, which has been shown to render children more vulnerable to certain health and developmental problems. Thus, when the babies are born, they will be tested for 22 genes known to be related to aggressive or antisocial behaviour, and to learning difficulties such as Attention Deficit Disorder. Michael Meaney and his group will also follow the cognitive and social development of these children for five years. Given the link between glucocorticoids, brain development, and memory, they will also perform brain scans and measure stress hormones levels throughout the study.

If the patterns observed in humans are comparable to data obtained in rats, Michael Meaney predicts that the children of mothers who are less engaged with their children may be predisposed to problems such as Attention Deficit Disorder. He cautions however, that these findings may not be as deterministic as they appear on the surface. Recent evidence from his laboratory suggests that these effects are reversible. If a pup from a low-licking mother is “adopted” by a high-licking mother, it shows normal development. This reversal can even occur if the pup is past puberty. Placing the pup into an enriched environment reverses the effects of early maternal care on stress responses and learning.

Moreover, Michael Meaney explains that having a higher response to stress is not always a bad thing. The environment one is raised in plays a very important role. One study, conducted in Montreal, in poor neighbourhoods with high crime rates, showed that boys who don’t get into trouble actually have higher cortisol levels than boys who join gangs and engage in criminal activity. He argues that their higher stress levels may make them more fearful and less likely to get into trouble.

Through this large countrywide effort, Michael Meaney and his colleagues may provide parents with insight into how they can help their children adapt to their environment and better prepare them to deal with stress. Moreover, the MAVAN project may potentially show HOW the complex interplay between our genes and the environment takes place.

Par Tania Elaine Schramek