What Role Might Placenta Play in Programming Mental Disorders?

The placenta is turning out to have unexpected connections with mental health and mental illness.

The research is being spearheaded by a young scientist awarded and funded by the Brain and Behavior Research Foundation (formerly known as NARSAD). He is Alexandre Bonnin, Ph.D., of the Department of Cell and Neurobiology at the University of Southern California's Keck School of Medicine.

It has been known for years that the placenta transfers oxygen and nutrients from the mother to the fetus. But what Bonnin and his colleagues have learned, through rodent research, is that the placenta also produces the neurotransmitter serotonin and releases it into the fetal bloodstream where it can reach the fetal brain. Thus, serotonin manufactured by the placenta putatively supplements whatever serotonin neurons the fetal brain makes.

"Since we demonstrated earlier that serotonin signaling is important for fetal forebrain wiring (by modulating axon guidance mechanisms), it suggests that the placental release of serotonin may be crucial for normal fetal brain wiring," Bonnin explained to Psychiatric News. "We are addressing this question by manipulating gene expression specifically in the placenta during pregnancy—in particular, we are trying to block placental serotonin synthesis by knocking out the [genes] required for its synthesis. Then we'll explore the effects of knocking out these placental genes on fetal forebrain development and adult brain function in the offspring. This research could provide important clues regarding the mechanisms of the fetal programming of adult mental disorders."

Bonnin and his group also plan to investigate the impact of maternal intake of SSRI antidepressants on placental physiology. "One of my goals," he said, "is to try to prevent placental transfer of the SSRIs by using specific molecular carriers.... The idea is to be able to treat maternal depression during pregnancy without affecting fetal development.... These studies will take advantage of [a] perfusion system for the mouse placenta that I developed recently."