Studies have shown that both human and rodent new mothers have reduced anxiety and reduced emotional reactions to negative events. Scientists think that this diminished anxiety allows mothers to focus on caring for and protecting their new offspring. However, researchers do not know what happens in the brain to cause the reduced anxiety.
To investigate this phenomenon, researchers funded by the Child Development and Behavior Branch compared levels of anti-anxiety proteins in the brains of four groups of rats: females who had just given birth, pregnant females, virgin females, and virgin males.
They hypothesized that the female rats that had recently given birth would have the highest levels of anti-anxiety proteins in their brains. However, they found no difference in levels of the proteins between the new mothers and the other rats.
The scientists concluded that the reduced anxiety may be caused by differences in other anxiety-related proteins in the brain (PMID: 21664440).