What causes hot flushes during menopause?

Hot flushes are not 'in the head,' but new research suggests they may start there; a UA research team has identified a region in the brain that may trigger the uncomfortable surges of heat most women experience in the first few years of menopause

Hot flushes affect millions of people, and not just women. Yet, it is still unclear what causes the episodes of temperature discomfort, often accompanied by profuse sweating.

Now a team of researchers around Dr. Naomi Rance, a professor in the department of pathology at the UA College of Medicine, has come closer to understanding the mechanism of hot flushes, a necessary step for potential treatment options down the road. This research was published recently in the Proceedings of the National Academy of Sciences.

The team identified a group of brain cells known as KNDy neurons as a likely control switch of hot flushes. KNDy neurons (pronounced "candy") are located in the hypothalamus, a portion of the brain controlling vital functions that also serves as the switchboard between the central nervous system and hormone signals.

"Although the KNDy neurons are a very small population of cells, our research reveals that they play extremely important roles in how the body controls its energy resources, reproduction and temperature," said Melinda Mittelman-Smith, who led the study as part of her doctoral thesis. "They are true multitaskers."

By studying KNDy neurons in rats, the research team created an animal model of menopause to elucidate the biological mechanisms of temperature control in response to withdrawal of the hormone estrogen, the main trigger of the changes that go along with menopause.

They discovered that tail skin temperature was consistently lower in rats whose KNDy neurons were inactivated, suggesting the neurons control a process known as vasodilation, or widening of the blood vessels to increase blood flow through the skin.

"The hallmark of hot flushes is vasodilation," explained Rance, who also is a neuropathologist at The University of Arizona Medical Center. "When you flush, your skin gets hot and you can see the redness of the skin. It is an attempt of the body to get rid of heat, just like sweating. Except that if you were to measure core temperature at that point, you would find it is not even elevated."

Although the results are not yet directly applicable in helping individuals affected by hot flushes, they mark a necessary first step, Rance said.

"Obviously we can't do these studies in women, and only if we understand the mechanism is there a chance of developing therapies. All that is known so far is that dwindling estrogen levels have something to do with it but anything after that is a black box."

"Right now the only effective way of treating flushes is estrogen-replacement therapy. If we could figure out what is causing those flushes, we could try to develop a better, more targeted therapy."