ory. In recent animal studies, Galea and her colleagues examined the effect of low and high levels of estradiol on working and reference memory. Working memory, or short-term memory, manipulates and retrieves information that is needed for a temporary task; it decays rapidly. Reference memory involves the long-term storage of information, and is stable over time. "When you remember where your car is in a shopping center parking lot on any given day, you're using working memory," explains Galea. "When you find the shopping center parking lot day after day, you're using reference memory."

In their study, Galea and her colleagues removed the ovaries from adult female rats (to eliminate naturally produced estrogens) and then gave the rats various levels of estradiol. "We found that low levels of estradiol improved the animals' working memory, but high levels impaired both their working and their reference memory," says Galea. In addition to modulating forms of learning and memory, estradiol influences cell growth in many areas of the brain--and, as Galea and her colleagues have found--estradiol's effects on that growth are different in the brains of males and females. In recent animal studies, Galea and her colleagues discovered that high levels of estradiol in females initially increased, then subsequently suppressed, the production of new brain cells in the dentate gyrus of the hippocampus, an area of the brain that is involved in learning and memory and that produces new neurons throughout life. This same pattern does not appear to be similar in the male brain. Once the new brain cells were formed, however, estradiol enhanced their survival differently in males and females. "In male rats, estradiol enhanced the survival of new cells only during a discrete period of time," says Galea, "but in females, the estradiol-induced enhancement of new neurons occurred during all the time periods tested."

As these and other studies show, estradiol has complex i
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Contact: Leah Ariniello
dawn@sfn.org
202-462-6688
Society for Neuroscience
24-Oct-2004

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