LEAD-EXPOSURE POTENTIATES THE EFFECTS OF NMDA ON REPEATED LEARNING

Several studies now suggest that Pb exposure disrupts NMDA receptor co mplex function, findings which may have implications for understanding the basis of Pb-induced learning impairments. To further evaluate thi s possibility, the behavioral properties of the glutamate agonist NMDA were compared in rats that had been chronically exposed to 0, 50, or 250 ppm Pb acetate in drinking water from weaning. Acute administratio n of NMDA (20-50 mg/kg IP) decreased accuracy in both the repeated acq uisition (RA) and performance (P) components of this multiple schedule with a selective effect on the learning component in the second half of the session. Analyses of error patterns revealed that the disruptio n of RA accuracy derived from initial perseverative errors followed by errors of skipping forward and backwards in the 3-member response seq uence. Response rates in both RA and P were suppressed by NMDA. Pb-exp osure potentiated the accuracy-impairing effects of NMDA by further in creasing the frequencies of these error classes, and likewise potentia ted the rate-suppressing effects of NMDA. These findings add further s upport to the possible involvement of Pb with the NMDA receptor comple x.