Lead exposure and agonistic behavior of adult mice of two ages

Adult male Heterogeneous stock (HET) mice were exposed to a 0.5% lead acetate solution when they were either 65 or 330 days of age. Fifteen weeks later they were paired with same age (young or old) water control HET mice and tested for aggression. All pairs of younger mice fought and six out of eleven pairs of older mice exhibited agonistic behavior. Although not all pairs of mice which fought achieved dominance, when dominant/subordinate relationships were established, the younger adults exposed to lead typically were subordinate. In contrast, older adults exposed to lead were always dominant. Differences in agonistic behavior patterns also were noted, with younger adults displaying more frequent and longer bouts of fighting than the older mice.