Postpartum aggression and plasma prolactin levels in mice exposed to lead

Young-adult, female Binghamton Heterogeneous Stock (HET) mice either were exposed to lead via drinking water from birth, or not. Eight days after giving birth to their first litter of pups (at about 70-75 days of age), postpartum aggression tests were conducted. Unfamiliar Het male intruders were introduced to the primiparous dams' nesting cages, and dyadic behavioral interactions were observed for 10 min. We also obtained plasma prolactin levels of these females, or others who had similar histories, but were not tested for maternal aggression. Behaviorally, the intensity of fighting was greater in lead-exposed pairs than in water-control pairs that fought. However, the percentage of pairs displaying aggressive behavior and average latency to initial contact were similar, regardless of dietary history. Plasma prolactin levels implied that lead exposure alone decreased circulating prolactin in primiparous Het dams eight days postpartum, but confrontation with a male intruder also was sufficient to reduce prolactin levels in water-control dams. It would be reasonable to assume that such changes in prolactin are dopaminergically mediated. The data suggest that lead ingestion may, in a species and strain specific manner, modify: 1) neurotransmitter and hormonal systems and 2) social behavior. The major effect of "subclinical" lead toxicity may be to change the limits of an organism's ability to cope with its environment.