Presentations

Abstract

Introduction: Astronauts will be exposed to space radiation (SR) during lengthy space expeditions like the planned Mars missions. Because the effects of SR cannot be studied experimentally in humans, our understanding of its effects depends on animal models. Using the balance beam (BB) task to test gross motor function, we have seen that SR causes substantial handicaps in rat performance. Studies are needed in additional animal models in order to fully understand the effects of SR on motor function in ways that will provide better insight into how SR may impact astronauts on deep space missions. In this study, we are comparing gross motor function and learning in mice and rats while also considering emotional and cross-species factors that may impact performance.

Methods: Male outbred, retired breeder C57BL/6 strain mice served as subjects. Animals were 8-9 months old at the start of study. Prior to behavioral experiments, mice were exposed to 15 cGy GCRsim and were individually housed (SR), or were individually housed (control; SHAM). At least 90 days following irradiation, time and age matched groups of mice began the BB task to assess gross motor function. The BB task uses a 1 meter long, 0.635 cm wide beam divided/marked lengthwise in equivalent sections (1, 2, 3, and 4/platform) and requires mice to traverse from a starting point to a goal box. When the animal is placed on the beam, the trial begins. The trial is considered over when the mouse has either succeeded (reached the goal box) or failed (fallen off the beam or 120 seconds has elapsed). They then return to their home cage for a 5 minute intertrial interval. Mice are trained starting at position 1 (closest to the goal box). If they succeed (all four paws reach the goal box) the next trial will start 1 position farther from the goal box (and so on to position 4), if they fail (120 second timeout or the mouse falls off) the next trial will start 1 position closer to the goal box (or position 1). This task consists of five trials per day for seven consecutive days.

Results: Male outbred, retired breeder C57BL/6 strain mice served as subjects. Animals were 8-9 months old at the start of study. Prior to behavioral experiments, mice were exposed to 15 cGy GCRsim and were individually housed (SR), or were individually housed (control; SHAM). At least 90 days following irradiation, time and age matched groups of mice began the BB task to assess gross motor function. The BB task uses a 1 meter long, 0.635 cm wide beam divided/marked lengthwise in equivalent sections (1, 2, 3, and 4/platform) and requires mice to traverse from a starting point to a goal box. When the animal is placed on the beam, the trial begins. The trial is considered over when the mouse has either succeeded (reached the goal box) or failed (fallen off the beam or 120 seconds has elapsed). They then return to their home cage for a 5 minute intertrial interval. Mice are trained starting at position 1 (closest to the goal box). If they succeed (all four paws reach the goal box) the next trial will start 1 position farther from the goal box (and so on to position 4), if they fail (120 second timeout or the mouse falls off) the next trial will start 1 position closer to the goal box (or position 1). This task consists of five trials per day for seven consecutive days.

Conclusion: We have implemented BB tests to assess gross motor performance and learning in mice and rats. Our preliminary data shows that differences in behaviors like fear responses and exploration will be important for understanding how the effects of SR impact animal model performance on tests like the BB. This data will help provide critical ground-based models of spaceflight hazards to better understand the effects of SR on astronauts during long-duration space flights and deep space missions.