In frightening situations, people tend to freeze, but not recent moms, who charge ahead. Now a new study shows how the brain speedily delivers the hormone oxytocin — which new mothers have in elevated levels, starting with childbirth — to where it’s needed, freeing them to protect their young.
The study, done in rats, revealed that oxytocin rushes to the brain region governing fear, called the amygdala, courtesy of special cells that act like a neurological expressway.
Further, when the researchers provoked these cells into sending oxytocin to the amygdala, it diminished the rats’ fearful responses to being startled.
The findings “could have implications for autism, anxiety and fear disorders,” said study researcher Ron Stoop, a psychiatric neuroscientist at the University of Lausanne in Switzerland. The work may also spur scientists to look more closely at the brain’s activity at moments when oxytocin levels are high, such as during childbirth and lactation, Stoop said.
The study is published in the February issue of the journal Neuron.
A hole in the wall
Oxytocin is produced in the hypothalamus, a marble-size region at the bottom of the brain, and released into blood. But the hormone also somehow makes its way into the rest of the brain, including the amygdala — a fact that has long-puzzled scientists, because the blood-brain barrier blocks oxytocin in the blood from moving into the brain.
From a previous experiment, Stoop’s team knew that oxytocin in the amygdala causes rats to remain in motion when they are scared, instead of freezing as they normally would.
“The main question was, ‘How does it get from hypothalamus to the amygdala?’” Stoop said. One idea was that oxytocin slowly diffused through the intervening brain tissue. But oxytocin affects the amygdala in “like, two seconds,” Stoop said — far quicker than the time it would take for diffusion.
Oxytocin had to be reaching its destination another way. To investigate, Stoop’s team infected rat hypothalamus cells with a virus that caused the cells to produce a glowing green protein whenever they produced oxytocin.