A new study in animals has found that chronic stress during pregnancy prevents brain benefits of motherhood, a finding that researchers suggest could increase understanding of postpartum depression.
Rat mothers showed an increase in brain cell connections in regions associated with learning, memory and mood. In contrast, the brains of mother rats that were stressed twice a day throughout pregnancy did not show this increase.
The researchers were specifically interested in dendritic spines - hair-like growths on brain cells that are used to exchange information with other neurons.
Previous animal studies conducted by lead author Benedetta Leuner of Ohio State University showed that an increase of dendritic spines in new mothers' brains was associated with improved cognitive function on a task that requires behavioural flexibility - in essence, enabling more effective multitasking.
The dendritic spines increased by about 20 percent in these brain regions in new mothers, according to her findings.
The stress in this new study negated those brain benefits of motherhood, causing the stressed rats' brains to match brain characteristics of animals that had no reproductive or maternal experience.
The stressed rats also had less physical interaction with their babies than did unstressed rats, a behaviour observed in human mothers who experience postpartum depression.
"Animal mothers in our research that are unstressed show an increase in the number of connections between neurons. Stressed mothers don't," said Leuner, assistant professor of psychology and neuroscience at Ohio State.
"We think that makes the stressed mothers more vulnerable. They don't have the capacity for brain plasticity that the unstressed mothers do, and somehow that's contributing to their susceptibility to depression," she added.
Leuner is continuing the work by investigating whether the beneficial effects of motherhood on cognitive functions are also blocked in mothers who are exposed to pregnancy stress as well as whether hormonal factors play a role.
She described the research during a talk Saturday in New Orleans at Neuroscience 2012, the annual meeting of the Society for Neuroscience. (ANI)