Researchers from Michigan State University (MSU) have found that microbes play an important role in shaping early brain development.

This is not a random effect, but a specific key brain region that controls stress, social behavior, and vital body functions.

The study, published in Hormones and Behavior, used a mouse model because mice share significant biological and behavioral similarities with humans.

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.

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.

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, the results were striking: All mice gestated by germ-free mothers had fewer neurons in the PVN, regardless of whether they received microbes after birth. The team 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 Alexandra Castillo Ruiz, lead author of the study and assistant professor in the MSU Department of Psychology.

"Rather than shunning our microbes, we should recognize them as partners in early life development. They're helping build our brains from the very beginning."