Glutamate and N-methyl-d-aspartate binding sites in the guinea pig hippocampus: Ontogeny and effect of acute in vitro ethanol exposure

The objectives of this study were to characterize the ontogeny of the l-glutamate (glutamate) and N-methyl-d-aspartate (NMDA) binding sites in the developing guinea pig hippocampus, and to determine the effect of acute in vitro ethanol exposure on these binding sites. Specific [³H]glutamate binding and NMDA-sensitive [³H]glutamate binding were determined using a guinea pig hippocampal synaptic membrane preparation (HSMP). To characterize the ontogeny of the density (B_max) and affinity (K_d) of the glutamate and NMDA binding sites, saturation analysis was conducted on HSMP of guinea pigs at gestational day (GD) 50 (immature fetus; term, GD 68), GD 62 (mature, near-term fetus), postnatal day (PD) 13 (neonate), and PD > 60 (adult). To examine the effect of ethanol on the glutamate and NMDA binding sites, HSMP of guinea pigs at GD 50, GD 62, PD 13, and PD > 60 was incubated with ethanol (0–100 mM), followed by determination of specific ['H]glutamate binding and NMDA-sensitive [³H]glutamate binding. To determine the effect of 50 mM ethanol on the B_max, and K_d of the glutamate and NMDA binding sites, HSMP of guinea pigs at GD 62 and PD > 60 was incubated with 0 or 50 mM ethanol followed by saturation analysis. The B_max, values of the hippocampal glutamate and NMDA binding sites were greater at GD 62 and PD 13 compared with GD 50 and PD > 60, but there was no change in the K_d of the binding sites throughout development. Ethanol did not alter hippocampal specific [³H]glutamate binding or NMDA-sensitive [³H]glutamate binding at any of the ages studied, and did not alter the hippocampal B_max or K_d of the glutamate or NMDA binding sites at GD 62 and PD > 60.