Effects of early experience on emotional and social reactivity in CBA mice

Abstract

During infancy some mice were handled and others were not handled in conjunction with their being reared in groups or isolation until adulthood. Emotional reactivity was assessed at 120 days of age by their activity in the open field, followed by measurement of plasma corticosterone levels, and social interaction was observed during their 15 weeks in a Reimer-Petras population cage, using a magnetic tagging technique. Handling and socialization produced a significant increase in open field activity, with the handled-socialization animals being the most active. Isolated animals had significantly higher plasma corticosterone levels than socialized animals, but the difference between handled and nonhandled males was not significant. The handled-socialized animals developed the most stable social hierarchy in the population cage, successfully differentiated roles, and had the lowest increase in systolic blood pressure. Isolated males failed to develop normal social behavior and severe fighting was observed throughout the 15 weeks; moreover, these animals had a higher elevation of systolic blood pressure than the socialized animals.