Maternal microbes play a significant role in shaping early brain development, study suggests

Research finds that microbes play an important role in shaping early brain development, specifically in a key brain region that controls stress, social behaviour, 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 behavioural 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.

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. 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.

. 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, 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.

This study shows that microbes play an important role in sculpting a brain region that is paramount for body functions and social behavior. In addition, the study indicates that microbial effects start in the womb via signaling from maternal microbes.

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, say the researchers.

Image source: Nature Journal 

Yvonne C. Milligan et al, The microbiota shapes the development of the mouse hypothalamic paraventricular nucleus, Hormones and Behavior (2025). DOI: 10.1016/j.yhbeh.2025.105742