The immune system may play a role in the development of postpartum depression after a stressful pregnancy, according to a new study based on a rat model.

Researchers from Ohio State University sought to examine the possible connection between the immune system, the brain and postpartum depression and discovered that areas of the brain associated with mood regulation showed signs of inflammation.

“Postpartum depression is understudied and, as a result, remains poorly understood,” said lead author Dr. Benedetta Leuner, an associate professor of psychology at Ohio State.

“Gaining a better understanding of the factors that contribute to this serious and prevalent disorder will be key to finding ways to better help women who are struggling.”

Around 15 percent of all new moms will experience postpartum depression, which has a variety of symptoms including prolonged depression, difficulty bonding with the baby, overwhelming fatigue and hopelessness.

“At least a half million women in the U.S. each year suffer from postpartum depression, and that is probably a low estimate. It’s surprising how little we know about how it arises,” Leuner said.

Most research has focused on hormonal reasons for the disorder, though some earlier work has been done on the immune system. In those studies, scientists investigated signs of inflammation in the blood and found mixed results.

The new study looked at the medial prefrontal cortex, a mood-related brain region previously implicated in postpartum depression.

During the research, rats were stressed during pregnancy to mimic a well-known risk factor for postpartum depression in human mothers. Similar to behaviors seen in women with postpartum depression, the stressed animals gave less attention to their offspring and exhibited depression- and anxiety-like behavior during various tasks.

And, unlike the non-stressed control rats, the stressed rats showed higher levels of inflammatory markers in their brain tissue, Leuner said. In addition, the researchers found evidence that the stress might lead to changes in how certain immune cells in the brain —  called microglia — function.

Study co-author Dr. Kathryn Lenz, an assistant professor of psychology at Ohio State, said she has become increasingly interested in the role of the immune system and its subsequent effects on the brain in mood disorders, including postpartum depression.

“It was especially interesting that we found no evidence of increased inflammation in the blood, but we did find it in this area of the brain that is important for mood regulation. We’re really excited because this suggests that inflammation in the brain may be a potential contributor to postpartum depression,” Lenz said.

“Eventually, this might provide a better target for treatment, whether through medication or other techniques such as meditation, diet and stress reduction,” she said.

The findings were recently presented at the annual Society for Neuroscience meeting in San Diego.

Source: Ohio State University