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 animals were concurrently injected with glutamate diethyl ester (GDEE), an antagonist of the glutamate receptor. When light-dark discrimination learning was carried out at 10 weeks old, the correct response in the acquisition period was impaired in the animals given 1 and 2 mg/g of neonatal MSG. Their retention scores were also impaired in comparison with the control animal. The behavioral impairment recovered with pre-treatment with GDEE. No significant changes were observed in the concentrations of transmitter substances, including amino acids and monoamines. These results suggest that neonatal MSG destroys the hippocampus and impairs acquisition and retention of discrimination learning through the mechanism of glutamate receptors.