The effects of different forms of estrogen replacement on hippocampal neurogenesis and cognition in young and older female rats.

Neurodegenerative diseases associated with aging, such as Alzheimer's disease (AD,) effect millions of people annually. The development of AD may be related to gonadal hormones present in adulthood. Interestingly, women have an increased risk for developing AD compared to men. Additionally, the disease progresses more rapidly in women and the onset of AD is generally earlier in women than in men. The ovarian hormone estrogen has been implicated as a possible therapeutic agent for improving cognition in postmenopausal women and AD patients, and epidemiologic evidence indicates that hormone replacement therapy (HRT,) reduces the incidence of and/or delays the onset of AD in women. However, there is evidence to suggest that the beneficial effects of estrogen on cognitive impairment associated with aging in women may depend upon the type of estrogen (e.g. estrone versus estradiol), taken. Interestingly, estrogens are known to exert significant structural and functional effects on the hippocampus, a brain region which retains the ability to produce new neurons throughout adulthood in all mammalian species studied, including humans, and is known to mediate some forms of learning and memory. Importantly, previous research has shown that the increased survival of newly produced neurons in the hippocampus of adult rodents are related to better hippocampus-dependent learning and memory. Cindy Barha is researching the effects of different types of estrogen on cognition and the production of new neurons in the hippocampus of young and older female rodents. The results of these experiments will have important implications for determining which alternative forms of estrogen to incorporate into HRT in the future. Ultimately, the results from these and other studies may lead to the development of new therapeutics that halt or slow the progression of neuronal loss in age-related neurodegenerative disorders.