NASA is planning to send a manned spacecraft to Mars by 2030. Interplanetary space travel puts astronauts at a high risk for exposure to several types of radiation exposure. This exposure has the potential to disrupt neurogenesis in the hippocampus, which has long been associated with learning and memory. This research proposes to study the effect of γ radiation on mossy fiber growth in the CA3 region of the hippocampus. Research has demonstrated that rats exhibit mossy fiber growth from the stratum lucidum to the stratum oriens of the hippocampus after completion of spatial learning. Water maze training is a spatial learning task that requires the animal to use distal cues to locate a platform hidden two centimeters below the water. Rats with a higher density of mossy fiber growth were expected to spend more time in the correct quadrant. This study investigated the effects of high dose single exposure radiation on presynaptic organization in the stratum oriens region of the hippocampus. Spatial learning was conducted using a water maze at a rate of ten trials per day for a period of four days. Five days after completion of spatial learning task, a probe test was completed. The delayed period was to allow for mossy fiber sprouting. The brain was then to extracted and sectioned at 30μm then stained with Timm’s staining. Timm’s stain allows visualization of metal such as zinc in newly formed axon terminals. A repeated measures ANOVA was conducted to determine if there was a significant difference between radiation and water maze performance. There were no other significant differences in spatial or probe performance. Hippocampal tissue was analyzed by measuring the area of stratum oriens with Timm’s staining present using grid point counting. There was no significant difference the in the area of Timm’s staining. These findings are consistent with current research, which suggests that there are no significant differences in behavioral learning or axon density immediately after exposure.

LLU Discipline

Clinical Psychology




School of Behavioral Health

First Advisor

Hartman, Richard E.

Second Advisor

Haerich, Paul E.

Third Advisor

Nelson, Gregory A.

Degree Name

Doctor of Philosophy (PhD)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Memory - Radiation effects; Hippocampus (Brain); Neurogenesis; Radiation Exposure; Central Nervous System - Radiation effects; Hippocampus - Radiation effects;

Subject - Local

Hippocampus; Mossy fiber growth; Spatial learning; Radiation; Behavioral learning



Page Count


Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


Loma Linda University Electronic Theses and Dissertations

Collection Website



Loma Linda University. Del E. Webb Memorial Library. University Archives