Ovarian Hormone Loss and Cognitive Decline at Multiple Timepoints during Aging
Engler, E.B.; Terry, D.P.; Millan, M.; Zay, C.; Crain, I.; and Bimonte-Nelson, H.A.
Department of Psychology, Arizona State University
In women, there is evidence that ovarian hormone loss at menopause exacerbates cognitive decline, although the specific relationship between age, memory loss, and hormones remains unclear. We have shown that ovariectomy (Ovx) in young rats is detrimental to, while Ovx in aged rats is beneficial to, spatial working memory. Since we found elevated progesterone (P) levels in ovary-intact aged rats, as well as that P reversed Ovx-induced memory enhancements in aged rats, we hypothesize that Ovx enhances memory in aged rats by removing the negative impact of P. The current experiment evaluated whether the age that Ovx transitions from detrimental to beneficial for spatial working memory corresponds with the age when P levels increase. We tested ovary-intact sham and Ovx female rats at 5, 12, 18, and 20 months of age on the water-escape radial-arm maze (WRAM), a working memory task. Spatial reference memory was assessed on the Morris water maze. For the WRAM, results showed that Ovx was detrimental to handling an increasing working memory load in 12 month-old females. On the contrary, Ovx enhanced the ability to handle an increasing working memory load in 18 and 20 month-old female rats. For the Morris water maze, Ovx aided in platform localization for 5 month-olds but impaired reference memory performance but exacerbating overnight forgetting in the 18 month-olds. Collectively, these data suggest that the effect of Ovx on maze performance depends not only on the age of the animal but also on the memory type being tested.