PREMENSTRUAL syndrome and postnatal depression could be caused by a shortage of receptors for a chemical messenger in the brain, researchers in Scotland believe. Both conditions are associated with a sudden drop in the amount of the female sex hormone oestrogen circulating in the blood. A team led by George Fink of the Medical Research Council鈥檚 Brain Metabolism Unit in Edinburgh has found that oestrogen stimulates the production of receptors that respond to serotonin 鈥� a mood-influencing chemical in the brain.
The finding explains why some women with premenstrual syndrome can be treated successfully with the drug Prozac, which increases levels of serotonin in the brain. It might also lead to the development of new treatments for premenstrual syndrome and the 鈥渂aby blues鈥�. 鈥淸It] is a very important step forward,鈥� says Angelika Wieck, a psychiatrist at the University of Manchester.
Fink鈥檚 team studied female rats which had had their ovaries removed, and so could not produce their own oestrogen. Half the rats were then given a dose of the hormone. Twenty four hours later, the researchers took slices from the animals鈥� brains, and found that the brain slices from the oestrogen-treated rats were able to take up more radioactively labelled serotonin 鈥� and so must have had an increased number of serotonin receptors. The researchers also found that oestrogen increases the activity of the gene that codes for the serotonin receptor in regions of the brain known to control mood. Fink described the findings at a meeting of the Physiological Society late last month.
Advertisement
The Edinburgh researchers are now checking that the mechanism discovered in the rats is also at work in women volunteers. They are using a brain imaging technique called single photon emission tomography, which can detect the presence of labelled serotonin, to see if the density of serotonin receptors in the brain changes during the menstrual cycle in line with levels of oestrogen.
Fink is confident that the results from these studies will mirror those from his rat experiments. He believes that oestrogen acts as a 鈥減sychoprotectant鈥�, warding off psychiatric problems by boosting the production of serotonin receptors. The fact that women are protected by oestrogen in this way could also explain why women schizophrenics usually develop the disease around 10 years later than men.