Birth by cesarean section is much more common in the U.S. than most of the rest of the world. The rate of births by c-section in the U.S. has also been getting higher -- around 32.9% of all babies delivered in 2009, an increase from 20.7% in 1996, according to the U.S. Centers for Disease Control.
Yale University researcher Tamas Horvath, a senior author on the PLoS ONE paper, doesn't specialize in researching childbirth issues. He was looking at how a protein called mitochondrial uncoupling protein 2, or UCP2, behaves inside the neurons of mice. In addition to brain development, UCP2 plays a role in breaking down fat - which suggests UCP2 might get kickstarted by natural birth as a way for a baby animal to transition to breast feeding.
Horvath said he and and his colleagues happened to notice - "completely serendipitously" -- that when they looked at the brains of mice, there was a clear difference in UCP2 levels between those delivered vaginally and those delivered via C-section.
When they looked closer, the researchers found that vaginal birth somehow triggers UCP2 expression in the neurons of the hippocampus, the brain region involved in both short and long-term memory as well as spatial orientation.
When they turned off the UCP2 gene or inhibited its function in adult mice, the animals performed differently in mazes than the normal mice. They explored less of the maze, tending to hug the walls and move more slowly than mice with normal UCP2 levels.
"Long lasting effects of impaired UCP2 activity during development may in fact affect complex adult behaviors," the researchers wrote.
Horvath says the next step towards determining if UCP2 has the same effects in humans is a bit unclear. He and his colleagues would like to look at another set of animals - probably dogs or pigs - born either vaginally or by C-section and follow them throughout their lives.
"The increasing prevalence of C-sections driven by convenience rather than medical necessity may have a previously unsuspected lasting effect on brain development and function in humans as well," he said in a statement.
SOURCE: Simon-Areces et al. "Ucp2 Induced by Natural Birth Regulates Neuronal Differentiation of the Hippocampus and Related Adult Behavior." PLoS ONE 7: e42911, 7 August 2012.