The system works like this. Dopamine is released into the space between two
nerve cells, stimulating the neighboring nerve cell. In normal animals, once
the signal has been sent, dopamine is taken back up by the dopamine transporters
into the cell from which it was released. This function is called dopamine reuptake.
“This,” says Wayne, “is what regulates the amount of dopamine
released in the brain and how much motivational drive we have to take drugs”.
When there is a decrease in the amount of dopamine transporters in the brain,
the dopamine reuptake does not happen as it normally would. This means the dopamine
signals last longer and are stronger than those in normal individuals.
Brake’s team also studied a number of genes in the front part or prefrontal
cortex of the rat’s brain. They found that several genes that are involved
in the development of the dopamine system were either turned on or off or changed
in their expression.
Wayne says all this appears to be regulated by the care a mother gives early
in the rat’s life. He explains, “while we don’t know a lot
about their (genes) exact nature, we do know that it may be important for generating
how the adult brain will be wired later on”.
The team plans to examine the genes individually to confirm the reliability
of the changes in the genes and to study their role in brain development.
Brake points out that although we cannot automatically translate the findings
in rats to humans, the study does show that in the brains of mammals, a mother’s
care is extremely important for brain development.
This study was funded by grants from the National
Institute on Drug Abuse, and the Canadian
Institutes of Health Research.