Physical Act of Birth Critical to Brain Development in Baby Mice

The actual act of birth in mice creates a "brain map" that the infant rodents use to process sensory information such as touch and vision, according to researchers, who found that the maps are created upon a marked reduction in serotonin levels upon being born.

Researchers from Kanazawa University in Japan say the findings highlight that the event of birth itself is a key in the development of neural circuits that are essential for survival outside of the womb.

"Our results clearly demonstrate that birth has active roles in brain formation and maturation," said senior study author Hiroshi Kawasaki. "We found that birth regulates neuronal circuit formation not only in the somatosensory system but also in the visual system. Therefore, it seems reasonable to speculate that birth actually plays a wider role in various brain regions."

Previous studies on brain maps have shown that the brain chemical serotonin plays a role in the development of these sensory maps, but until now, its specific role during normal development has been unclear.

Kawasaki and his team's research suggests that upon birth, the drop in serotonin levels triggers the formation of neural circuits in a region of the rodent brain known as the barrel cortex, which processes tactile information, and the lateral geniculate nucleus (LGN), a brain region that processes visual information.

"When mice were treated with drugs that either induced preterm birth or decreased serotonin signaling, neural circuits in the barrel cortex as well as in the LGN formed more quickly. Conversely, neural circuits in the barrel cortex failed to form when the mice were treated with a drug that increased serotonin signaling, suggesting that a reduction in levels of this neurotransmitter is crucial for sensory map formation," the researchers wrote in a statement.

Kawasaki said that because serotonin also plays a key role in mental disorders, any sort of abnormal birth that disrupts the natural serotonin reduction upon birth could affect brain development.

"Uncovering the entire picture of the downstream signaling pathways of birth may lead to the development of new therapeutic methods to control the risk of psychiatric diseases induced by abnormal birth," Kawasaki said.

The research is published in the Cell Press journal Developmental Cell.