The placenta is unique among organs—critical to human life yet fleeting. In its short time of duty, it serves as a vital protective barrier to the fetus. The organ’s blood vessels—which resemble tree roots in this image by Norman Barker, associate professor of pathology at the Johns Hopkins University School of Medicine—also deliver essential oxygen and nutrients from the mother to her developing baby. Still, the placenta has been vastly underappreciated. Scientists are taking a closer look and finding that it is much more than a simple conduit: it actively protects the fetus and shapes neurological development.
In a study published last summer, British researchers showed that when a mother mouse is deprived of food, the placenta takes over, breaking down its own tissue to nourish the fetal brain. Scientists at the University of Southern California’s Zilkha Neurogenetic Institute (ZNI) and their colleagues, meanwhile, upended decades of biological dogma when they reported that it is the placenta—not the mother—that provides the hormone serotonin to the fetus’s forebrain early in development. Because hormones play an essential role in brain wiring, even before they function as neurotransmitters in the brain, placental abnormalities could directly influence the risk of developing depression, anxiety and even autism. As a result, “we have to pay much closer attention to the health and welfare of the placenta,” says Pat Levitt, director of the ZNI and the study’s co-author.
Research into the placenta’s influence on the developing brain is so new it has yet to be named. Anna Penn, a developmental neurobiologist and neonatologist at Stanford University, has dubbed it “neuroplacentology.” Penn herself is studying the impact of placental hormones on fetal brain development after the 20th week of gestation. Her goal: to pinpoint how premature babies are affected by the loss of those hormones at delivery and, ultimately, to figure out a way to compensate for the deficit. The old thinking about the placenta is changing, Penn says, but there is still much to learn.