Abstract
Complex maze learning was investigated in male neonatal and adult rats using a latent learning task. The neonates received (intragastric administration) either lead acetate (50 mg Pb/kg) or equimolar sodium acetate on days 6, 9, 12, and 18 postpartum. The adult subjects were exposed to 100 ppm Pb acetate or equimolar sodium acetate in drinking water for 112 days beginning at weaning (day 21 postpartum). Training for the latent learning task began on day 31 postpartum for the neonates and on day 143 for the young adults. The training sequence included free exploration (under conditions of satiation) of a symmetrical latent learning maze or an open field of the same shape and area by the Pb-treated and control subjects (randomly distributed). Subsequently, all subjects were food deprived and appetitively tested in the latent learning maze. Neonatal lead exposure perturbed latent learning: the Pb-treated subjects showed no evidence of latent learning. However, pretest exploratory activity was similar for Pb-exposed and control neonates. Pb exposure had no effect on exploratory activity under normal (nonappetitive) conditions or latent learning performance of young adult subjects despite the increased body burden of Pb. The results suggest that latent learning may be a particularly sensitive measure of Pb exposure in the neonatal rat model.