| Summary: | Estradiol can influence a variety of physiological and psychological processes.
This hormone has been shown to influence learning and memory processes. The effects
of physiological levels of estradiol on spatial working memory performance were
explored in Chapter 1. In Experiment 1, daily systemic estradiol or oil injections were
administered to adult, ovariectomized female rats approximately 4 hours prior to the
testing on a win-shift version of the radial arms maze. A high dose of estradiol (5 μg
estradiol benzoate) enhanced acquisition of the task whereas a low dose (0.3 μg estradiol
benzoate) impaired working memory performance. Experiment 2 was conducted to
examine site-specific influences of estradiol on spatial working memory in well-trained
rats. Saline and two doses of estradiol cyclodextrin (0.1 μg and 0.9 μg estradiol/0.5 μL
saline) were infused into the prelimbic region of the prefrontal cortex and dorsal
hippocampus 40 minutes prior to testing on the win-shift task. The higher dose of
estradiol facilitated working memory when infused into the prelimbic region, whereas
lower doses of estradiol facilitated performance when infused into the hippocampus.
Working memory performance was significantly impaired 24 hours after infusions of
estradiol into the dorsal hippocampus relative to saline infusions. These data provide
further evidence for the idea that estradiol can dose-dependently alter memory processes,
and also suggest that the facilitation and impairment of working memory by estradiol is
site- and time-specific. Chapter 2 sought to elucidate the role of long-term physiological
levels of estradiol on the phosphorylation of cAMP response binding element (pCREB); a
transcription factor related to cognitive processes. Ovariectomized rats were
administered oil, high estradiol (5 μg estradiol benzoate) or low estradiol (0.3 μg estradiol
benzoate) for 17 consecutive days. Neither dose of estradiol significantly altered the
number of pCREB-positive cells in the dorsal CA1, CA3 or in the prelimbic region
relative to control levels. There was however a time of day effect, with animals perfused
40 minutes after the last injection exhibiting more pCREB-positive cells than animals
perfused 4 hours after the last injection. Future research is required to clarify the role that
estradiol plays in the activation of CRJEB. === Medicine, Faculty of === Graduate
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