Journal
NEUROBIOLOGY OF LEARNING AND MEMORY
Volume 90, Issue 1, Pages 155-163Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.nlm.2008.04.002
Keywords
estrogen; ovariectomy; spatial memory; reference memory; water maze; aging; rat
Funding
- NIA NIH HHS [AG023925-01, R01 AG028084, R01 AG028084-01A2, R03 AG023925, R03 AG026137, R03 AG026137-01] Funding Source: Medline
- NIDA NIH HHS [P50 DA16511, P50 DA016511] Funding Source: Medline
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The current study investigated whether, for spatial reference memory, age impacts (I) sensitivity to surgical ovarian hormone loss (Ovx), (2) response to estradiol therapy (ET), and (3) the relation between circulating estradiol levels and memory scores in ovary-intact sham and Ovx plus ET rats. Young, middle-aged and aged Fischer-344 rats received sham, Ovx or Ovx plus ET treatments, and were then tested on the Morris maze. After the last test trial, a probe trial was given whereby the platform was removed. Circulating estradiol levels were then determined and correlated with performance. In Study 1, Ovx facilitated learning on day one, but impaired performance after day one, in young rats. Ovx did not influence performance in middle-aged rats. In young and middle-aged Ovx rats, ET enhanced performance with higher exogenous estradiol levels correlating with better performance during testing and the probe trial. There was no relationship between endogenous estradiol levels and performance in sham young or middle-aged rats. Study 2 showed that, like middle-aged rats, aged rats were not impacted by Cvx. Further, for aged Cvx rats, the ET regimen that was beneficial at earlier ages was no longer effective during test trials, and had only minor benefits for platform localization as assessed by the probe trial. Collectively, the findings suggest that the effects of Ovx as well as responsivity to the currently utilized ET regimen changes with age. Further, there appears to be a distinction between sensitivity to Cvx and responsiveness to ET after Ovx for spatial reference memory performance. (C) 2008 Elsevier Inc. All rights reserved.
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