Chronic exposure to estrogen impairs some cognitive functions

Veterinary biosciences professor Susan Schantz and graduate student Victor Wang found that rats exposed to estradiol were significantly impaired on tasks involving working memory and response inhibition. Click here for more information.

University of Illinois researchers report this week that chronic exposure to estradiol, the main estrogen in the body, diminishes some cognitive functions. Rats exposed to a steady dose of estradiol were impaired on tasks involving working memory and response inhibition, the researchers found.

Their report appears this week in the journal Behavioral Neuroscience.

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.

Working memory is the ability to briefly remember information needed for a particular task, said Susan Schantz, a U. of I. professor of veterinary biosciences and principal investigator on the study. An example in humans is a phone number that is forgotten soon after the number is dialed.

"With working memory you're just keeping it active until you use it," she said.

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 Those that alternated between the levers (which were withdrawn from the rat enclosure for a few seconds between trials) received a reward.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," Schantz said. The estradiol-treated rats "were not as good at waiting," she said.

"Rats treated with estradiol are definitely a lot more active and make a lot more lever presses," said neuroscience graduate student Victor Wang, the lead author on the study. "That's not conducive toward being rewarded."