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Researchers Tomas Paus, a neuroscientist who specializes in the developing brain and neurogenetics and his wife Zdenka Pausova, an expert in cardiology, metabolism and genetics at their home office in Toronto.JENNIFER ROBERTS

He studies the brain. She focuses on the heart and body. But Tomas Paus and his wife Zdenka Pausova have joined forces to understand how the brain and body influence each other in the development of depression, cardiovascular disease and other disorders.

The couple recently returned to Canada from England to launch an ambitious, multigenerational study of families from different ethnic groups in Toronto.

Their goal is to learn more about the genetic and environmental factors that shape our brains and our metabolisms and can lead to such problems as addiction, obesity and hypertension, also known as high blood pressure.

Does how reactive someone is to stress affect whether they become obese? Are there structural differences in the brain that mean people prefer fatty diets or that they are not easily satiated when they eat? Does adversity in early childhood affect weight gain or drug use in adolescence?

These are some of the questions they hope to answer by doing detailed brain and body scans of thousands of volunteers. Participants will also provide blood samples and answer questions about what they eat and how they live.

Ideally, Dr. Paus and Dr. Pausova would like to follow individuals from childhood through to old age, but they say that is extremely difficult. The next best thing is to recruit multigenerational families - children, parents and grandparents - to study the interplay between genes and the environment.

One of their goals is to find new ways to tell whether an adolescent is susceptible to a particular disease.

"We want to look at early risk factors and subclinical signs in adolescence that diseases are already starting before the symptoms are apparent," says Dr. Pausova, 47. She studies cardiovascular health in adolescence and has taken a position at Toronto's Hospital for Sick Children.

Dr. Paus, 48, a neuroscientist and one of the world's leading experts on the adolescent brain, has joined Baycrest's Rotman Research Institute.

They are both from the Czech Republic, but moved to Montreal in 1990 and stayed for 15 years. They became Canadian citizens and raised their daughter there, but left five years ago for the University of Nottingham and an opportunity to work together on how the brain influences the body, and vice versa.

They came back to Canada in part because the Rotman Research Institute committed to raise the $10-million needed for the new Toronto Trans-generational Brain and Body Centre.

It's their dream project, a more ambitious version of a study they began in the Saguenay region of Quebec five years before they left Canada. It involved nearly 600 adolescents between the ages of 12 and 18.

They applied for grants separately, but studied the same group. Dr. Paus found, for example, that exposure to cigarette smoke in the womb appears to affect brain development and behaviour in adolescence. A part of the brain known as the orbital frontal cortex was thinner in the children whose mothers had smoked during pregnancy. Those children were also more likely to have experimented with drugs.

In lab animals, exposure to nicotine in the womb influences the reward circuitry in the brain and how they respond to psychoactive drugs later in life.

Dr. Pausova found that girls exposed to nicotine in the womb were more likely to put on weight late in adolescence.

The Saguenay study also yielded intriguing insights into differences in how the male and female brain develop in adolescence. In the boys, the volume of white matter in the brain increased by 25 per cent between the ages of 12 and 18. White matter connects different parts of the brain together and the rapid growth appears to be mediated by testosterone. In girls, the changes were less dramatic, about a 5-per-cent increase in white matter.

The new Toronto study will allow them to explore questions raised by their earlier work, such as whether low levels of testosterone are linked to depression and whether slightly higher blood pressure in the teenage years is related to hypertension later in life.

"We know that many disorders or pathologies, whether in the brain or the body, develop over the lifetime. So there are trajectories that need time to develop. Some start as early as in utero, some later in childhood or even in middle age. But you need to know what is happening in the lifespan," Dr. Paus says.

The opportunity to do this kind of work lured them back to Canada, but they say they also returned because they missed their adopted country.

"We like Canada … its mentality - if one can say that about a country - and ways of doing things," she says.

They work long hours, and because they collaborate so closely they tend to discuss their research at home. But they say they also like to ski, go to movies and enjoy good meals with their friends.

Body scans to reveal where fat is stored

Where does your body store fat? The body scans that will be done as part of the multigenerational Toronto study will allow researchers to see now much fat is deposited in different parts of the body. Some people store most of their fat in regular fat tissue, but in others it builds up in the liver or muscles, which can lead to insulin resistance, says Zdenka Pausova, who studies obesity and hypertension. This in turn can lead to diabetes.

But even among people who put most of their fat into regular fat tissue, it tends to build up in the abdomen rather then being spread around the body. This is often linked to high blood pressure.

Some of the information could be used to help the volunteers improve their health.

"It is so interesting to learn about yourself and your whole family, and how much fat you have in your tummy," says Tomas Paus, her husband and partner in the research.

"It's a great educational opportunity. They can sit down in the evening and show each other the scans, and can learn about what they are doing right and not doing right in terms of lifestyle."