Brainstem auditory evoked response at five years and prenatal and postnatal blood lead

Previous work from this laboratory demonstrated an association between high er maternal blood lead level at 20 weeks of pregnancy and increased I-V and III-V interpeak intervals in the brainstem auditory evoked response (BAER) recorded in 1-month-old infants. We repeated the BAER measurements with a larger group of children (n = 100-113) from the same study at 5-7 years. Ma ternal blood lead level at 20 weeks of pregnancy (geometric mean = 7.7 mu g /dl; range 1-30.5 mu g/dl) was the only prenatal blood lead level significa ntly associated with I-V and III-V interpeak interval in a multiple regress ion model controlling for head circumference and age at time of testing and sex. In contrast to the findings at 1 month of age, interpeak intervals de creased as a linear function of increasing 20-week maternal blood lead. A n onlinear, orthogonal, second-order polynomial model was a significantly bet ter fit to the data than the linear model. The nonlinear model showed I-V a nd III-V interpeak intervals decreased as blood lead rose from 1 to 8 mu g/ dl, and then increased as blood lead rose from 8 to 30.5 mu g/dl. We hypoth esized that the negative linear term was related to lead effect on brainste m auditory pathway length, and that the positive quadratic term was related to neurotoxic lead effect on synaptic transmission or conduction velocity. We found support for the brainstem length interpretation in the data, show ing that 6-year-old head circumference in these children significantly decr eased with increased maternal 20-week blood lead level. Increasing postnata l blood lead at 12 and 48 months was related only to decreased BAER conduct ion intervals across the entire blood lead range, suggesting only pathway l ength effects. Alterations in BAER at this age may indicate that the effect of prenatal lead exposure on the auditory brainstem is permanent, as respo nse latencies reach essentially adult values by 4 years of age. (C) 2000 El sevier Science Inc. All rights reserved.