Date of Award

8-1-2002

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Abstract

The purpose of this study was to examine the impact of long-term exposure to corticosterone (CC) and chronic zinc-deprivation (ZnD) on memory performance and hippocampal damage in rats. Previous work has examined the impact of exposure to CC or the impact of ZnD, but no previous work has examined the combined impact on memory performance. Previous work suggests that chronic exposure to CC or ZnD results in hippocampal damage and memory deficits.

The present study utilized a broader range of memory tests than previous studies and administered the memory tests early and late in the time period of CC exposure and ZnD. CC is released as a part of the stress response and is initially beneficial to the organism in maintaining homeostasis. However, with chronic exposure to stress and subsequent chronic CC release, damage to the cell bodies and neurons of the hippocampus have been found. This is problematic because the hippocampus plays a role in memory and learning mechanisms. Memory problems are also present in stress-related disorders such as post-traumatic stress disorder (Bremner, 1999) and depression (Sheline et al., 1996).

The hypotheses of this study were that hippocampal degeneration as a result of long-term CC exposure and ZnD would result in decreased long- and short-term spatial memory in Sprague-Dawley rats with a greater decrease in memory in ZnD rats as compared to ZnA (Zinc-adequate) animals. Degeneration of the neurons of the hippocampus would also be apparent in the CC treated animals with more degeneration exhibited in the ZnD rats than the ZnA animals, and this would correspond to greater deficits found in memory.

Results indicated a general decrease in performance was found for the CC animals as compared to control animals on the memory tasks. A decrease in the hippocampus area CA3 pyramidal cell layer width was observed in the animals treated with CC. Performance on the radial arm maze was significantly correlated with the width of the CA3 pyramidal cell layer. Performance on the water maze was significantly correlated with the concentration of zinc in the vesicles in the CA1 and CA3 areas of the hippocampus.

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