Early life affects mental health

March 13, 1998

Next Wednesday is European Brain Day. The THES gets cerebral

A clear link exists between early life events and brain development, according to neuroscientists at Nottingham University. The researchers believe it offers important clues about how humans' social environment affects their mental health.

The brains of laboratory rats who are separated from their mothers and kept in social isolation develop "markedly" differently compared with those of rats kept in larger groups, a team of researchers from the Nottingham Neuroscience Group has found.

The mature brains of the isolated rats show lower levels of the brain chemical serotonin, a neurotransmitter associated with mood. Low levels of serotonin in humans are linked to clinical depression.

Anti-depression drugs, such as Prozac, are used to reduce feelings of depression in humans by increasing serotonin activity in the brain. The illegal drug Ecstasy produces similar but more intense effects on serotonin levels.

The researchers, led by Charles Marsden, have shown that changing simple environmental factors in early years can lead to neurobiological developments that raise serotonin levels and reduce the likelihood of depression.

"The clear inference of our findings is that perhaps some of our modern approaches to child rearing and so on are not appropriate," Professor Marsden said.

"I have to be careful, as this goes outside neuroscience, but it tells us that we need to look very carefully at the social environment in which we grow up," he said. "When you are little you need a lot of stimulation. The more parents play with their children, the less risk the children have of depression."

Professor Marsden said that incidences of depression are increasing rapidly in society, especially among men. "I would say the link between our lifestyles and the general increase in depression needs to be investigated."

The researchers measured chemical levels in the rats' brains during post-mortems but also measured the release of the chemicals in live rats through "in vivo micro-dialysis", which involves inserting a fine probe into the living brain. "The good thing about the brain," Professor Marsden said, "is that it feels no pain."

Professor Marsden, who will present some of his findings on March 18, European Brain Day, said that the brain's chemical make-up can often predispose people to mental illnesses such as clinical depression. "But depression is usually a combination of existing brain functioning and events that happen during life."

The researchers have also made links between early life events and schizophrenia. The brains of the isolated laboratory rats, as well as showing lower levels of serotonin, showed above-average levels of the chemical dopamine, which is associated with schizophrenia. Anti-schizophrenia drugs reduce the function of dopamine in the brain.

The isolated rats, Professor Marsden found, are less susceptible to "drugs of abuse" such as amphetamines and cocaine, which act on dopamine levels. The rats require higher doses of such drugs to feel the "rewards".

Simple tests can show whether the rats associate drugs of abuse with reward, Professor Marsden said. The rats are taught to associate an injection of the drugs with a light, white box. Given a choice between a white box and a black box, those rats that enjoyed the experience of the drugs will go to the white box, in the hope of more reward. Those that did not go to the black box.

"All the systems in the brain that make us feel happy are less effective in the brains of isolated rats," Professor Marsden said.

* The European Dana Alliance for the Brain is coordinating European Brain Day. Its website is at http://www.dana.org

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