DIFFERENTIAL EXPERIENCE FOLLOWING DEVELOPMENTAL LEAD-EXPOSURE - EFFECTS ON BRAIN AND BEHAVIOR

Long Evans hooded rat pups were exposed to lead (Pb) via the maternal milk supply from Postnatal Day 1 (PN 1) to PN 25. Mothers were fed diets containing either 4% Pb CO3 (High Pb), 0.4% Pb CO3 (Low Pb) or 2.2% Na2 CO3 (Controls) throughout this period. Pups were weaned at PN 30 and littermates randomly assigned to either an Enriched or Isolated environment for a period of 30 days. Increases in activity levels and decreases in passive avoidance latencies were observed in Pb exposed animals. However, there were minimal effects due to Pb on symmetrical maze performance. Experience in the enriched environment had no effect on open field activity levels but resulted in a marked reduction in symmetrical maze errors. While enrichment had no effect on passive avoidance performance in High Pb animals, it was capable of raising latencies in Low Pb animals to Control values. Thus, the therapeutic value of environmental enrichment in Pb exposed animals depends on both the task employed and the severity of the pre-enrichment brain damage. From both brain regional analysis and behavioral testing results, it appeared that the hippocampus was a major site of Pb action. From comparison of blood Pb levels of our animals and those reported in children, it became apparent that the rat may have a greater tolerance for Pb, and as such, caution must be used in making direct comparisons between the two species in terms of blood Pb levels. © 1979.