Environmental Effects on Open-Field Behavior: Differences Between Two Strains of Inbred Mice

Hill, Elizabeth, and Sylvia Malcore

Environmental effects on behaviors related to ‘anxiety’ or fear have been consistently demonstrated for many species, including laboratory mice. In addition, fear responses have been shown to vary between inbred strains of mice. In this study, we subjected mice from two commonly-used laboratory strains to an early environmental intervention. In one condition, mouse pups were separated from the mother on five occasions and exposed to predator cues (fox odor and recorded owl calls), while in a control condition, pups were exposed only to home cage bedding. After maturation, the mice were observed in an open field test (n=35). As expected, strain differences emerged. Compared to the C57BL/6 mice, BALB/c mice spent more time in the sheltered areas of the apparatus, rather than the open center area (center seconds, C57B: 18.5+7.3s, BALB: 6.9+6.4s, p<.001). Seconds spent in a shelter were higher for the BALB mice in the first and second parts of the observation period, but a third fear measure, defecation pellets deposited, did not differ by strain. Group differences (predator cue condition) were not statistically significant, but a trend was seen. Surprisingly, the predator-exposed group tended to spend less time in the shelter during the test (HC: 167.7+116.7s, PE: 98.8+86.2s; p<.08). The two strains did not differ in measures of behavioral development (day 10) nor in growth before weaning (weights days 4, 10, and 21). Future research will examine whether the impact of this early environmental intervention varies by strain, and also how the intervention affects other behavioral dimensions.