Low level lead exposure during lactation increases rough and tumble play fighting of juvenile rats.

Lactating rats were given distilled water or distilled water containing 0.067% lead chloride (500 ppm lead) as their sole source of drinking fluid from Days 1-21 of lactation. Activity, social investigation and rough and tumble play fighting behaviors of the offspring were observed on Day 26 and activity and play solicitation behaviors on Day 36. Although lead treatment reduced the mothers' fluid intake, there were no effects on pup growth and activity or on maternal behaviors. When paired with a group-housed stimulus animal on Day 26, lead-treated subjects had increases in the two measures of play fighting (crossover and pinning), and in social investigation, relative to controls. When tested with a scopolamine-treated, non-playful stimulus on Day 36, increased crossover frequencies were observed in lead-treated subjects when compared with controls. Two-min activity levels on Days 26 and 35 were unaffected by lead exposure. These results indicate that social interactive behaviors of juvenile rats are effective tools in the assessment of exposure to toxic substances early in development.