Behavioral effects of early lead exposure and subsequent toxocariasis in mice

Lead and behavioral development: effects of varying dosage and schedule on survival and performance of young common terns (Sterna hirundo)

Exposure to lead early in life is known to affect behavioral development. Young common terns (Sterna hirundo) were injected with lead nitrate solution (0.2-1.2 mg/g) or sterile saline to examine the dose-response curve for behavioral effects. Exposed chicks received a dose of lead on d 3 or on d 3 and 7. Behavioral tests 2 d after each injection included visual cliff performance, locomotion, and righting response. Survival depended not only on dose but also on whether chicks received one or two injections. Despite the narrow range of doses, behavioral differences were noted for all measures as a function of dose. The initial lead dose affected behavior more than the second dose, despite the fact that birds receiving a divided dose were more likely to die.

The impact of single versus repeated exposure of mice to Toxocara canis

Infection with T. canis can alter dramatically the brain and behavior of the host. Previous results suggest that if the mammalian host is exposed either simultaneously to lead, or has a history of prior exposure to that toxic substance, the magnitude of the behavioral reaction to T. canis may be modified or even reduced. The present data suggest that the magnitude of both the behavioral and tissue/immune reactions may be less if the organism has multiple, instead of a single exposure, to T. canis. Lead, and perhaps other environmental toxicants may alter neurotropic products of the parasite, the behavior of the parasite, and/or reactivity of the host in the presence of the parasite. Such considerations may help explain, in part, the relative rarity of reported toxocariasis in humans, despite the fact that serological indices suggest that exposure to T. canis may be as high as 7% of the world population.