Low level lead effects on activity under varying stress conditions in the developing rat.

The study was designed to determine whether lead ingestion by nursing rats would affect the way offspring reacted to the stress inducing properties of the test environment both as juveniles and mature rats. Dams were exposed to diets with 0.0, 0.2, 0.4 or 1.0 percent by weight metallic lead. Mean blood-lead levels of pups at weaning were 4, 25, 36 and 55 micrograms/100 ml of blood respectively. The stress factor was varied by (1) changing the test apparatus, i.e., forcing rats to occupy an open field or allowing the animal to be a free agent in the start box of a T-maze; (2) testing rats under a longitudinal and a cross-sectional experimental design to vary familiarity with the apparatus; and (3) comparing behavior in the presence or absence of noise. Reactivity was assessed by examining the inter-and intra-session pattern of ambulations and defecations. Analysis of data revealed that lead treated rats demonstrated the greater response to stress. This response was generally dose related although recovery was dependent upon the test applied and measures taken. The findings provide a conceptual framework to account for varied results across previous studies.