NEONATAL GLUTAMATE CAN DESTROY THE HIPPOCAMPAL CA1 STRUCTURE AND IMPAIR DISCRIMINATION-LEARNING IN RATS

Neonatal Wistar rats were subcutaneously injected with 0.1, 1, or 2 mg /g b.wt. of monosodium glutamate (MSG) at 1, 3, 5, 7, and 9 days after birth. The animals were observed for degeneration of pyramidal cells in the hippocampus. The histological change disappeared when the anima ls were concurrently injected with glutamate diethyl ester (GDEE), an antagonist of the glutamate receptor. When light-dark discrimination l earning was carried out at 10 weeks old, the correct response in the a cquisition period was impaired in the animals given 1 and 2 mg/g of ne onatal MSG. Their retention scores were also impaired in comparison wi th the control animal. The behavioral impairment recovered with pre-tr eatment with GDEE. No significant changes were observed in the concent rations of transmitter substances, including amino acids and monoamine s. These results suggest that neonatal MSG destroys the hippocampus an d impairs acquisition and retention of discrimination learning through the mechanism of glutamate receptors.