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Menstrual Cycle May Alter Brain Chemistry

Hormonal changes may actually alter the chemical balance in the brain and trigger some of the mood swings associated with a woman's monthly menstrual cycle, according to a new study.

The study suggests that cells in a brain region called the hippocampus generate different types of receptors for the brain chemical GABA during various phases of the menstrual cycle. These changes may affect a woman's susceptibility to anxiety, depression, and seizures.

Both estrogen and progesterone have effects on nerve cell activation, but the mechanism behind changes in seizure activity and increased anxiety are unknown, write the researchers.

They say their study may offer a new molecular basis for the severe anxiety and depression some women experience in the week or so before their period, known as premenstrual dysphoric disorder -- PMDD. This may also explain why many women with epilepsy suffer more seizures during this time.

The results of the study appear in the journal Nature Neuroscience.

Previous studies have shown that 78 percent of epileptic women have more seizures before menstruation occurs. Seizures in women with epilepsy that are triggered by hormonal changes are called catamenial seizures. This occurs during a part of their menstrual cycle when the levels of the hormone progesterone are low.

In addition, about 5 percent of women with PMDD regularly experience severe anxiety and depression during this time frame, but the reasons behind these changes are unclear.

Biological Basis for Bad Moods

In this study, researchers found that mice produced more of a particular type of receptor that inhibited the action of GABA during the part of the menstrual cycle when progesterone levels were low.

This caused a dramatic reduction in the normally soothing action of GABA on the brain and increased the risk of seizures and anxiety.

During the part of the menstrual cycle when progesterone levels were high and estrogen levels were low, they found the reverse was true. During this part of the cycle the mice were less susceptible to seizure and anxiety.

Therefore, researchers say that these GABA-receptor changes may be responsible for seizure risk and anxiety levels seen in women with catamenial epilepsy and PMDD.

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Maguire, J. Nature Neuroscience, advance online edition, June 2005.