New research from Michigan State University finds that microbes play an important role in shaping early brain development, specifically in a key brain region that controls stress, social behavior, and vital body functions.
The study, published in Hormones and Behavior, used a mouse model to highlight how natural microbial exposure not only impacts brain structure immediately after birth but may even begin influencing development while still in the womb. A mouse model was chosen because mice share significant biological and behavioral similarities with humans and there are no other alternatives to study the role of microbes on brain development.
This work is of significance because modern obstetric practices, like peripartum antibiotic use and Cesarean delivery, disrupt maternal microbes. In the United States alone, 40% of women receive antibiotics around childbirth and one-third of all births occur via Cesarean section.
“At birth, a newborn body is colonized by microbes as it travels through the birth canal. Birth also coincides with important developmental events that shape the brain. We wanted to further explore how the arrival of these microbes may affect brain development,” said Alexandra Castillo Ruiz, lead author of the study and assistant professor in the MSU Department of Psychology.
The research team focused on a brain region called the paraventricular nucleus of the hypothalamus (PVN), which plays a central role in regulating stress, blood pressure, water balance, and even social behavior. Their previous work had shown that mice raised without microbes, or germ-free mice, had more dying neurons in the PVN during early development. The new study set out to determine whether this increased cell death translated to changes in neuron number in the long run, and if any effects could be caused by the arrival of microbes at birth or if they began in the womb via signals from maternal microbes.
To find out, the researchers used a cross-fostering approach. Germ-free newborn mice were placed with mothers that had microbes and compared them to control groups. When the brains of these mice were examined just three days after birth, results were striking: All mice gestated by germ-free mothers had fewer neurons in the PVN, regardless of whether they received microbes after birth. They also found that germ-free adult mice had fewer neurons in the PVN.
“Our study shows that microbes play an important role in sculpting a brain region that is paramount for body functions and social behavior. In addition, our study indicates that microbial effects start in the womb via signaling from maternal microbes,” said Castillo-Ruiz.
Rather than shunning our microbes, we should recognize them as partners in early life development,” said Castillo-Ruiz. “They’re helping build our brains from the very beginning.”