Researchers have puzzled over why certain mental health disorders occur more frequently and severely among one gender but not the other.

Examples include autism and schizophrenia, which are more common and severe among boys than girls, yet the biological basis for this difference between the two sexes is unknown.

Using animal models, researchers at the University of Maryland School of Medicine have discovered differences in the development of the amygdala region of the brain – which is critical to the expression of emotional and social behaviors.

The investigators believe this finding may help to explain why some mental health disorders are more prevalent among boys.

They 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 behavior, specifically how they played.

The study results are published online this month in the Proceedings of the National Academy of Sciences.

Margaret M. McCarthy, Ph.D., senior author and a professor of physiology and psychiatry at the University of Maryland School of Medicine, 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 litter mates.

They also found that the females had lower amounts of endocannabinoidsUniversity of Maryland Medical Center