Estradiol and soy extract increase the production of new cells in the dentate gyrus of old rats

In young rodents, estradiol increases cell proliferation in the dentate gyrus of the hippocampus. However, it is unknown if the old brain retains this response to estradiol. Here we assessed the generation of new cells in the dentate gyrus of old rats after administration of estradiol or a soy extract, since soy is used as an alternative to hormonal replacement therapy in postmenopausal women. In a first experiment, 12-month-old animals were ovariectomized and studied at 14, 18 or 22 months of age. The production of new cells, assessed by the incorporation of bromodeoxyuridine (BrdU), was similar in 14- and 18-month-old rats. However, there was a significant reduction in the number of BrdU-immunoreactive cells at 22 months of age. In a second experiment, 22-month-old ovariectomized animals were treated for 10 weeks with a weekly s.c. injection of 150 μg estradiol valerianate or with 60 mg/kg per day soy extract added to the drinking water. Both treatments increased significantly the production of new cells in the dentate gyrus. These findings indicate that the brains of old rats retain the ability to increase the production of new cells in response to estradiol and soy extracts.