Myelin Deficits Produced by Early Postnatal Exposure to Inorganic Lead or Triethyltin Are Persistent

Abstract: Long-Evans rat pups were exposed to either inorganic lead (400 mg Pb as lead acetate/kg body weight/day) or triethyltin sulfate (1.0 mg/kg body weight/day), by gastric intubation, from 2 days through 29 days of age. The rats were then weaned and placed on standard lab chow ad libitum. At 30 days of age, leadtreated rats exhibited statistically significant decreases in body and brain weights (22% and 17%, respectively), and the concentration of forebrain myelin was significantly reduced, by 21% relative to the 4.9 mg myelin protein/g brain in control rats. Although these animals recovered from the body weight deficits after several months, the deficits in brain weight and myelin concentration were still present at 120 days of age. This suggests that the lead-induced myelin deficits were permanent. Lead levels in brain, which were maximal at 30 days of age when the treatment was terminated, decreased more slowly than in other organs and were still 30% of maximal levels at 120 days of age. Triethyltin-treated animals also had significantly decreased body and brain weights (20% and 11%, respectively) at 30 days of age, and an even more severe reduction in forebrain myelin concentration (33%). These animals also regained a normal body weight by 120 days of age, but again the deficits in brain weight and myelin concentration persisted. Tin levels in brain and other organs had decreased to control levels by 60 days of age. Animals malnourished by maternal deprivation to match the body weights of the treated animals had myelin deficits that were less severe than those in the treated animals at 30 days of age (approximately 11% less than controls); however, these myelin deficits also persisted throughout the subsequent 90-day recovery period examined. The apparent lack of recovery from CNS myelin deficits produced by neonatal exposure to different heavy metals or to malnutrition reemphasizes the vulnerability of the developing nervous system to a wide range of metabolic insults.