From the article:
Changes in the estrogen receptor have been associated with age-related memory deficits and an increased incidence of Alzheimer’s disease among women In addition, previous studies have shown estrogen replacement may improve cognition in postmenopausal women and younger women with low estrogen levels. Estrogen also appears to protect against Alzheimer’s disease and dementia.
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The mice had unusually low levels of estrogen because their ovaries were removed at an early age. However, scientists were still able to rescue learning ability by delivering the correct gene to produce estrogen receptor-alpha directly to the hippocampus.
Mice that lacked the estrogen receptor showed poor ability to locate a platform hidden in a small swimming tank over a training period of several days. After receiving the gene, the mice learned to locate the platform in two days of training.
[…]
Recordings made from the brain tissue of treated mice showed signals were strongly communicated across the gaps, or synapses, between hippocampal cells, similar to what would happen with estrogen replacement.