According to the experts, women have a higher incidence of depression, post-traumatic stress disorder, and other anxiety disorders than men do. Why? A new study may hold the answer.

The new study found that females are more sensitive to low levels of an important stress hormone and less able to adapt to high levels of it than males. The study was done on rats, but researchers think that because rats have some of the same neural systems as humans, the research could have implications for humans.

The study, conducted by behavioral neuroscientists at The Children's Hospital of Philadelphia, focused on a hormone called corticotropin-releasing factor (CRF) that is released in the brain of humans and rats in response to stress. CRF is a neurotransmitter — in other words, it helps brain cells communicate. 

Researchers analyzed the brains of rats as they responded to a stress test aimed to trigger the release of the CRF hormone. The female rats were more responsive and less adaptive to the hormone than their male counterparts.

In females, the CRF "receptors" were bound more tightly to the hormone than those found in males. This made the females react more intensely to stress than males. Also, after exposure to stress, male rats reduced the number of CRF receptors in their brains, making them less responsive to the hormone. Female rats didn't display this adaptation to stress. In other words, they continued to feel the stress for longer periods than the males.

So, can this rodent research be applied to humans? Who knows. But it is the precursor to similar studies that would involve humans. It is significant because most of the previous animal research on stress disorders used only male rodents, so important sex differences may have gone undetected.