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The hormone estrogen is the reason why females respond better to stress, a new animal study suggests.

Females are more resilient than males when under stress, but scientists have never really understood why. Researchers from the study, published in the journal Molecular Psychiatry, said the latest findings offer a scientific explanation as to why females are better at combating stress.

"We have examined the molecular mechanism underlying gender-specific effects of stress," senior author Zhen Yan, PhD, a professor in the Department of Physiology and Biophysics in the University at Buffalo School of Medicine and Biomedical Sciences. "Previous studies have found that females are more resilient to chronic stress and now our research has found the reason why."

Among rats exposed to repeated episodes of stress, researchers found that females respond better than males because of the protective effect of estrogen.

Researchers found that young female rats exposed to one week of periodic physical restraint stress showed no impairment in their ability to remember and recognize objects they had previously been shown.  On the other hand, young males exposed to the same stress had worse short-term memory.

Researchers explained that the stressors used in the experiments mimic challenging and stressful, but not dangerous, experiences that humans face, like those causing frustration and feelings of being under pressure.

Yan and her team were able to make males respond to stress more like females and females more like males by manipulating the amount of estrogen produced in the brain.

"When estrogen signaling in the brains of females was blocked, stress exhibited detrimental effects on them," explained Yan. "When estrogen signaling was activated in males, the detrimental effects of stress were blocked.

Researchers said that female rats whose ovaries were removed still responded better to stress.  Yan said the findings suggest that the protective effect may come from estrogen produced in the brain.  

Further analysis revealed that the enzyme aromatase, which produces estradiol, an estrogen hormone, in the brain, is responsible for female stress resilience. Researchers found that aromatase levels are significantly higher in the prefrontal cortex of female rats.

"If we could find compounds similar to estrogen that could be administered without causing hormonal side effects, they could prove to be a very effective treatment for stress-related problems in males," she said, adding that while stress itself is not a psychiatric disorder, it can sometimes trigger the development of mental disorders in vulnerable individuals.