For reasons still unknown, the brain neurotransmitter serotonin is critical to the development and treatment of depression and chronic anxiety. An even a bigger mystery is why more women than men are affected by depression and chronic anxiety.

Hristina Jovanovic, Swedish medical university Karolinska Institute, believes he may be able to show why women are affected by depression and chronic anxiety. Using a PET scanner he was able to show that men and women differ in the number of binding sites for serotonin in certain parts of the brain.

Women have a greater number of the most common serotonin receptors. Women also have lower levels of the protein that transports serotonin back into the nerve cells, which is the same protein that most common antidepressants (SSRIs) block. For women who are symptom free during their menstrual cycle also appear to have a serotonin system that is more flexible and responds to hormone swings.