Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Developmental, neural and hormonal aspects of sexually-dimorphic spatial learning (Morris water-maze) in meadow voles (Microtus pennsylvanicus) and deer mice (Peromyscus maniculatus) were examined in this thesis. The first study examined seasonal changes in sexually-dimorphic spatial ability in adult deer mice. A sex difference in spatial learning favoring males was evident during breeding season, while there was no evidence of a sex difference during the non-breeding season. Male spatial performance was increased during the breeding season relative to the non-breeding season while the reverse pattern was observed in females. The second study examined developmental changes in spatial learning in voles. Postweaning voles (Day 20 and 25 after birth) acquired the task more quickly than did preweaning voles (Day 10). No sex difference in water-maze performance was evident at any juvenile age. The third study investigated re-acquisition of the same task in these same voles as adults. Sex differences favoring males were observed in voles that were born into female-biased litters, though only in the voles that had previously been tested before weaning. This suggests an organizational effect of testosterone or its metabolites on sexually-dimorphic spatial learning. The fourth study examined the relationship between gonadal hormones and spatial learning in adult meadow voles. Females with high levels of estradiol performed more poorly in the water maze than both males and females with low levels of estradiol. The final study examined the relationship between hippocampal volume, spatial learning and gonadal hormone level. High Testosterone males had larger hippocampi than low testosterone males during the breeding season, while High Estradiol females had larger hippocampi than Low Estradiol females. Together the results of these studies show that sexually-dimorphic spatial ability is associated with both organizational (in utero) and activational effects of gonadal hormones, as well as prior experience. These studies provide the first demonstration of the influence of natural changes in reproductive status on spatial learning, and additionally demonstrate that spatial performance of males and females is differentially affected by and related to changes in reproductive status.



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