Date of Award

7-13-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

First Advisor

Jeffrey N. Weatherly

Abstract

The discovery of the Ames dwarf mouse in the early 1960s has given researchers an exciting opportunity to study the hormonal effects of aging. The Ames dwarf mice have a recessive mutation of the PROP-1 gene that causes hereditary dwarfism. The abnormality produced an anterior pituitary deficiency which resulted in the lack of growth hormone, thyroid-stimulating hormone, and prolactin. Researchers noticed that these mice were smaller than their normal siblings but lived approximately twice as long. The purpose of the present research was to determine if the reduced hormones in the Ames dwarf mouse delay the loss of memory and the ability to learn. Learning was assessed using matching-to-sample procedures, while memory was evaluated using a modified radial-arm procedure. The animals were assigned to five groups according to their age and genetic composition. The potential differences in learning and memory were investigated between young Ames dwarf mice (3-5 months) and their normal siblings vs. old Ames dwarf mice (18-21 months) and their normal siblings vs. very old Ames dwarf mice (32-35 months). Due to the prolonged life of the very old Ames dwarf mice, they do not have normal living siblings. For most of the measures in the present study, the age of the animals had little to do with their performance on any of the procedures. However, the overall results showed no differences in accuracy between any of the groups of mice or a behavioral decline as the mice age. These results are consistent with the theory of a delayed age-related behavioral decline in the Ames dwarf mice. Another main result of the study showed that an effect of genotype was observed. However, upon closer analysis, the Ames mice performed just as accurately on all of the measures as the control mice. The only major difference was that the Ames dwarf mice did not complete as many trials per session as the control mice. This result shows that the Ames dwarf mice had a slower performance during the procedures. Taken together, all of the results suggest that the Ames dwarf mice performed as well as the control mice, but did so in a delayed manner.

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