Differences in the development of the amygdala region of the brain, which is in-charge of emotion and social behaviour, was studied by researchers in animal models which explains the reason for the greater incidence of some mental disorders in males.
Experts at the University of Maryland School of Medicine also found a surprising variable - a difference between males and females in the level of endocannabinoid, a natural substance in the brain that affected their behaviour, specifically how they played.
"Our findings help us to better understand the differences in brain development between males and females that may eventually provide the biologic basis for why some mental health conditions are more prevalent in males," said Margaret M. McCarthy, senior author and a professor of physiology and psychiatry at the University of Maryland School of Medicine.
"We need to determine if these neural differences in the developing brain that we've seen in rats may cause similar behavioural effects in human babies," she added.
McCarthy and her colleagues found that female rats have about 30 to 50 percent more glial cells in the amygdala region of the temporal lobe of the brain than their male littermates.
They also found that the females had lower amounts of endocannabinoids, which have been dubbed the brain's own marijuana because they activate cannabinoid receptors that are also stimulated by THC, the main psychoactive ingredient of cannabis.
Researchers also found that the female rats also played 30 to 40 percent less than male rats.
However, when these newborn female rats were given a cannabis-like compound to stimulate their natural endocannabinoid system, their glial cell production decreased and they displayed increased play behavior later as juveniles.
"We have never before seen a sex difference such as this in the developing brain involving cell proliferation in females that is regulated by endocannabinoids," said McCarthy.
"The results of this study provide important clues to brain differences between males and females and may increase our knowledge about how these differences may affect both normal and aberrant brain development, thereby enhancing our understanding of many mental health disorders, said E. Albert Reece, vice president of medical affairs at the University of Maryland.
The results have been published online in the Proceedings of the National Academy of Sciences.