Effect of developmental lead exposure on the expression of specific NMDA receptor subunit mRNAs in the hippocampus of neonatal rats by digoxigenin-labeled in situ hybridization histochemistry.

The N-methyl-D-aspartate (NMDA) receptor has an important role in learning and memory. In this study, the effects of chronic Pb exposure on NMDA receptor subunit mRNAs expression in the developing rat hippocampus were examined by digoxigenin (DIG)-labeled in situ hybridization. In Pb-exposed rats, hippocampal NR1-2a mRNA levels were significantly increased in CA1, CA4 and DG subfields at 15 days of age and CA4 and DG subfields at 20 days of age. The lead (Pb) exposure resulted in a significant increase of NR2D mRNA levels in CA1, CA2, CA4 and DG hippocampal subfields at 20 days of age. Hippocampal NR2A mRNA levels were significantly decreased in CA1, CA2, CA3 and DG subfields from 15-day-old Pb-exposed rats and CA1, CA3 and DG subfields from 20-day-old Pb-exposed rats. Hippocampal NR3A mRNA levels were also significantly decreased in CA1, CA4 and DG subfields at 15 days of age and CA1 and DG subfields at 20 days of age in Pb-exposed rats. The Pb-induced subunit specific changes in hippocampal NMDA receptor subunit mRNA expression may lead to abnormality of natural NMDA stoichiometry and interfere with the physiological function of the NMDA receptor in the development of defined neuronal connections.