Differences in the brain's serotonin system between men and women could explain why women are more likely to suffer from conditions such as depression, fibromyalgia and irritable bowel syndrome.

Scientists from the Swedish medical university Karolinska Institutet say they have detected differences in the way serotonin is handled between the sexes. This has implications for diseases in which serotonin is thought to play a role.

Serotonin is one of a group of chemicals known as neurotransmitters which are used to transmit messages in the brain and nervous system. Serotonin is specifically involved in the regulation of mood and pain. Treatments for depression and anxiety such as the popular ' selective serotonin reuptake inhibitor' (SSRI) drugs, such as Prozac, are thought to work by increasing lvels of serotonin in the brains of sufferers. Likewise, drugs for irritable bowel syndrome (IBS) target serotonin receptors in the gut (of which there are vast numbers) to control pain and bowel function.

These conditions are all more common in women, as are others thought to have a serotonin connection such as fibromyalgia.

Researchers from the Karolinska Institutet used PET scans to look at the serotonin systems in the brains of both men and women. What they found was that women tended to have larger numbers of the most common serotonin receptors than men in certain brain regions. Women were also found to have lower levels of the protein which transports serotonin back to the nerve cell that secreted it.

Associate professor Anna-Lena Nordström, lead researcher on the study said: "We don't know exactly what this means, but the results can help us understand why the occurrence of depression differs between the sexes and why men and women sometimes respond differently to treatment with antidepressant drugs."

The researchers have also demonstrated that the serotonin system in healthy women differs from that in women with serious premenstrual mental and emotional symptoms. These findings suggest that the serotonin system in women who experience severe PMS is less able to adapt to changes in hormonal levels throughout the menstrual cycle, leading to fluctuating levels of serotonin and other brain chemicals which leads to mood disturbances and other symptoms.

Professor Nordström and colleagues suggest that treatments for depression should be tested seperately on men and women to account for the differences in serotonin function they have discovered. The same may also be worthwhile in other conditions in which serotonin plays a role and which are more prevalent amongst women.

 Source: Karolinska Institutet

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