Chronic exposure to estradiol, from genistein supplements or soy-based foods, appears to diminish some cognitive functions such as working memory and response inhibition, say University of Illinois researchers.
The researchers made the discovery when studying the effects of estradiol on activities mediated by the prefrontal cortex, a brain region that is vital to working memory and to the ability to plan, respond to changing conditions and moderate or control one's behavior. Their report appears this week in the journal Behavioral Neuroscience.
Working memory is the ability to briefly remember information needed for a particular task. An example in humans is a phone number that is forgotten soon after the number is dialed.
In the new study, rats were trained to press one of two levers to obtain a food reward. Those that alternated between the levers (which were withdrawn from the rat enclosure for a few seconds between trials) received a reward. Those that hit the same lever twice in a row got no reward. Rats exposed to estradiol performed worse than their counterparts on this task, earning significantly fewer rewards.
A second set of tests measured the rats' ability to wait before responding to a stimulus. The rats had to wait 15 seconds before pushing a lever to get a reward. Those exposed to estradiol performed worse on this task than those that were not exposed. "That's the test where we really saw the most striking effects with estradiol," researcher Susan Schantz said. The estradiol-treated rats "were not as good at waiting."
"Rats treated with estradiol are definitely a lot more active and make a lot more lever presses," added co-researcher Victor Wang. "That's not conducive toward being rewarded."
The researchers had not expected to see such pronounced results. They originally planned to compare the effects of chronic estradiol exposure to the effects of chronic exposure to genistein, a phytoestrogen found in soybeans. Genistein is believed to have similar effects in the body as natural or synthetic estrogens, although no study has definitively proven that it does.
Some women take genistein supplements to reduce hot flashes or other symptoms of menopause. "Women take them thinking they'll be a safe alternative to hormone-replacement therapy and they might help hot flashes," Schantz said.
The new research indicates that multiple factors influence the effects of estradiol on the brain, Schantz said. The timing of the exposure, the types of brain functions or structures studied and the age of the test subjects can all generate different results, she concluded.
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Source: University of Illinois at Urbana-Champaign