Our bodies are colonized by trillions of microbes that help regulate countless biological processes. Now, new research suggests these microbes may begin shaping the brain even before birth.
A team at Georgia State University studied newborn mice raised in germ-free environments. Some were placed with mothers who had normal microbiota, allowing researchers to track when microbial influences began. Their focus was the paraventricular nucleus (PVN) of the hypothalamus, a brain region tied to stress and social behavior.
The findings were striking: germ-free mice had fewer neurons in the PVN, even if microbes were introduced right after birth. This suggests microbial influence begins in the womb, during prenatal brain development, not just after delivery.
Long-Lasting Changes
The neural differences persisted into adulthood. Adult germ-free mice still showed reduced neuron numbers in the PVN compared with mice exposed to microbes. While the cross-fostering experiments were not extended into full adulthood, the early signs show that microbial exposure—or the lack of it—can have lasting consequences.
“Birth coincides with critical developmental events in the brain,” said neuroscientist Alexandra Castillo-Ruiz, who led the study. “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.”
Why It Matters for Humans
Though the study was conducted in mice, there are enough biological parallels to suggest similar processes may happen in humans. Practices such as Cesarean sections and antibiotic use around birth are already known to disrupt microbial transfer, which could have subtle but meaningful effects on brain development.
Potential consequences may include changes in stress regulation and social behavior, both of which are linked to the PVN. While definitive conclusions in humans are still far off, the findings highlight the importance of maternal gut health during pregnancy.
The Next Steps
Future research could explore whether adjusting the microbiota of expectant mothers might influence fetal brain development. Previous studies have already tied gut microbes to diet, sleep, alcohol intake, and overall health.
“Our study shows that microbes play an important role in sculpting a brain region that is paramount for body functions and social behavior,” said Castillo-Ruiz. “And importantly, these effects begin in the womb through signaling from maternal microbes.”
The study has been published in Hormones and Behavior.
