April Flowers for redOrbit.com – Your Universe Online
Precise, well-characterized maps crucial for translating perception into understanding are built in the brain by neurons that process sensory information such as touch and vision. A new study from Kanazawa University of Japan reveals that the brain chemical serotonin is reduced in newborn mice during the act of birth. This reduction triggers sensory maps to form in the brain. The findings, published in the journal Developmental Cell, demonstrate the key role of a dramatic environmental event in the development of neural circuits, revealing that birth itself is one of the triggers that prepares the newborn for survival outside the womb.
“Our results clearly demonstrate that birth has active roles in brain formation and maturation,” says Hiroshi Kawasaki, Professor of Molecular and Developmental Medical Neuroscience of Kanazawa University. “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.”
From mice to humans, mammals have brain maps representing various types of sensory information. Neurons that process tactile information from whiskers are found in a region of the rodent brain called the barrel cortex. These neurons are arranged in a map corresponding to the spatial pattern of whiskers on the snout, with neighboring columns of neurons responding to stimulation of adjacent whiskers. Prior studies have shown that the neurotransmitter serotonin directs the development of sensory maps. However, the specific role that serotonin plays during normal development has been unclear until now.
The current study finds that the birth of the mice pups leads to a drop of serotonin levels in the newborn mouse’s brain. This triggers the formation of neural circuits in the barrel cortex and in the lateral geniculate nucleus (LGN), a brain region that processes visual information. Neural circuits in the barrel cortex and the LGN formed more quickly when mice were treated with drugs that either induced preterm birth or decreased serotonin signaling. In contrast, when the mice were treated with a drug that increased serotonin signaling, neural circuits in the barrel cortex failed to form. This suggests that a reduction in levels of this neurotransmitter is crucial for sensory map formation.
Serotonin is known to play a key role in mental disorders, leading the research team to question whether it is possible that abnormalities in birth processes and the effects on subsequent serotonin signaling and brain development could increase the risk of psychiatric diseases. “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 says.