The cognitive effects of ovariectomy and estrogen replacement are modulated by aging
Section snippets
Subjects
F344 female rats (retired breeders) were acquired from the Hiltop Laboratory Colony (Hiltop Laboratory Animals, Scottdale, PA, USA) at 12–13 (n=65) and 20 months (n=90) of age. An additional group of rats at 6 and 10 months of age (20–22 rats per age group) were received from the same source to estimate the aging-related changes in the estrus cycle by means of vaginal cytology and estrogen concentration in the plasma. Food and water were provided ad libitum. Animals with obvious health problems
Changes in the estrous cycle and in the levels of estrogen in blood with aging and in the course of estrogen withdrawal and replacement
The duration of the estrus cycle (number of days between consecutive estruses) was significantly increased between 13 and 14 and 21 months of age (F(3,53)=27.37, P<0.0001, Fig. 1). The elongation in the duration of the estrus cycle was accompanied by a significant decrease in the number of cycles that included the proestrus stage (F(3,53)=5.62, P<0.005). However, the first sign of age-related changes in the estrus cycle was already revealed between 10 and 13–14 months of age in regularity of
Discussion
In the present study, we examined the cognitive effects of ovariectomy and estrogen replacement during aging and a possible involvement of the cholinergic system in mediating these effects. By using the T-maze active-avoidance paradigm, we showed that short-term estrogen withdrawal and estrogen replacement did not affect the escape or avoidance behavior in both middle-aged and old Fischer-344 females. However, when the cholinergic system was compromised by scopolamine, both types of estrogen
Acknowledgements
This study was supported by NIA grant AG15947 to A.L.M. The authors would like to thank Drs. J. Simpkins and S. Ross for generous help with the processing of the estrogen assays, Y. Aguirre, J. L. Morton, K. Phelan, and D. Waters for their assistance with behavioral testing and J. L. Morton for editorial help.
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2020, Hormones and BehaviorCitation Excerpt :There has been a multitude of research indicating that the loss of ovarian hormones —particularly estrogens following surgical ovary removal — is detrimental to not only various body systems, but also to memory in humans (Nappi et al., 1999; Rocca et al., 2007; Sherwin, 2003) as well as in animal models (for review, see: Daniel, 2013; Frick, 2015; Koebele and Bimonte-Nelson, 2015; Korol and Pisani, 2015; Luine, 2014). Furthermore, under certain administration conditions, E2 treatment following ovariectomy (Ovx) can improve learning and memory performance in a variety of animal models (e.g., Bimonte and Denenberg, 1999; Black et al., 2018, 2016; Bohacek et al., 2008; Fernandez et al., 2008; Harburger et al., 2009; Koebele et al., 2020; Lacreuse, 2006; Markowska and Savonenko, 2002; Prakapenka et al., 2018; Rapp et al., 2003; Rodgers et al., 2010; Savonenko and Markowska, 2003; Talboom et al., 2008; Wallace et al., 2006). However, not all estrogens behave in an identical fashion.
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